No brakes on the fix train

Revert "Split the project into packages."

.gitignore

@@ -6,6 +6,7 @@
 
 # Zig ignore
 **/zig-cache/
+**/.zig-cache/
 **/zig-out/
 **/build/
 **/build-*/

build.zig

@@ -4,10 +4,10 @@ const builtin = @import("builtin");
 const rt = @import("test/runtime_test.zig");
 const RuntimeStep = rt.RuntimeStep;
 const Allocator = std.mem.Allocator;
-const Builder = std.build.Builder;
+// const Builder = std.build.Builder;
 const Step = std.build.Step;
 const Target = std.Target;
-const CrossTarget = std.zig.CrossTarget;
+const CrossTarget = std.Target.Query;
 const fs = std.fs;
 const File = fs.File;
 const Mode = std.builtin.Mode;
@@ -16,12 +16,12 @@ const ArrayList = std.ArrayList;
 const Fat32 = @import("mkfat32.zig").Fat32;
 
 const x86_i686 = CrossTarget{
-    .cpu_arch = .i386,
+    .cpu_arch = .x86,
     .os_tag = .freestanding,
-    .cpu_model = .{ .explicit = &Target.x86.cpu._i686 },
+    .cpu_model = .{ .explicit = &Target.x86.cpu.i686 },
 };
 
-pub fn build(b: *Builder) !void {
+pub fn build(b: *std.Build) !void {
     const target = b.standardTargetOptions(.{ .whitelist = &[_]CrossTarget{x86_i686}, .default_target = x86_i686 });
     const arch = switch (target.getCpuArch()) {
         .i386 => "x86",
@@ -156,7 +156,7 @@ pub fn build(b: *Builder) !void {
         try qemu_args_al.append("none");
     }
 
-    var qemu_args = qemu_args_al.toOwnedSlice();
+    const qemu_args = qemu_args_al.toOwnedSlice();
 
     const rt_step = RuntimeStep.create(b, test_mode, qemu_args);
     rt_step.step.dependOn(&make_iso.step);
@@ -197,7 +197,7 @@ const Fat32BuilderStep = struct {
     step: Step,
 
     /// The builder pointer, also all you need to know
-    builder: *Builder,
+    builder: *std.Build,
 
     /// The path to where the ramdisk will be written to.
     out_file_path: []const u8,
@@ -217,7 +217,7 @@ const Fat32BuilderStep = struct {
     ///     Fat32.Error     - If there was an error creating the FAT image. This will be invalid options.
     ///
     fn make(step: *Step) (error{EndOfStream} || File.OpenError || File.ReadError || File.WriteError || File.SeekError || Fat32.Error)!void {
-        const self = @fieldParentPtr(Fat32BuilderStep, "step", step);
+        const self: *Fat32BuilderStep = @fieldParentPtr("step", step);
         // Open the out file
         const image = try std.fs.cwd().createFile(self.out_file_path, .{ .read = true });
 
@@ -237,7 +237,7 @@ const Fat32BuilderStep = struct {
     /// Return: *Fat32BuilderStep
     ///     The FAT32 builder step pointer to add to the build process.
     ///
-    pub fn create(builder: *Builder, options: Fat32.Options, out_file_path: []const u8) *Fat32BuilderStep {
+    pub fn create(builder: *std.Build, options: Fat32.Options, out_file_path: []const u8) *Fat32BuilderStep {
         const fat32_builder_step = builder.allocator.create(Fat32BuilderStep) catch unreachable;
         fat32_builder_step.* = .{
             .step = Step.init(.custom, builder.fmt("Fat32BuilderStep", .{}), builder.allocator, make),
@@ -255,7 +255,7 @@ const RamdiskStep = struct {
     step: Step,
 
     /// The builder pointer, also all you need to know
-    builder: *Builder,
+    builder: *std.Build,
 
     /// The target for the build
     target: CrossTarget,
@@ -293,7 +293,7 @@ const RamdiskStep = struct {
 
         // First write the number of files/headers
         std.debug.assert(self.files.len < std.math.maxInt(Usize));
-        try ramdisk.writer().writeInt(Usize, @truncate(Usize, self.files.len), endian);
+        try ramdisk.writer().writeInt(Usize, @truncate(self.files.len), endian);
         var current_offset: usize = 0;
         for (self.files) |file_path| {
             // Open, and read the file. Can get the size from this as well
@@ -305,14 +305,14 @@ const RamdiskStep = struct {
             // Write the header and file content to the ramdisk
             // Name length
             std.debug.assert(file_path[file_name_index..].len < std.math.maxInt(Usize));
-            try ramdisk.writer().writeInt(Usize, @truncate(Usize, file_path[file_name_index..].len), endian);
+            try ramdisk.writer().writeInt(Usize, @truncate(file_path[file_name_index..].len), endian);
 
             // Name
             try ramdisk.writer().writeAll(file_path[file_name_index..]);
 
             // Length
             std.debug.assert(file_content.len < std.math.maxInt(Usize));
-            try ramdisk.writer().writeInt(Usize, @truncate(Usize, file_content.len), endian);
+            try ramdisk.writer().writeInt(Usize, @truncate(file_content.len), endian);
 
             // File contest
             try ramdisk.writer().writeAll(file_content);
@@ -333,7 +333,7 @@ const RamdiskStep = struct {
     ///     Errors for opening, reading and writing to and from files and for allocating memory.
     ///
     fn make(step: *Step) Error!void {
-        const self = @fieldParentPtr(RamdiskStep, "step", step);
+        const self: *RamdiskStep = @fieldParentPtr("step", step);
         switch (self.target.getCpuArch()) {
             .i386 => try writeRamdisk(u32, self),
             else => unreachable,
@@ -352,7 +352,7 @@ const RamdiskStep = struct {
     /// Return: *RamdiskStep
     ///     The ramdisk step pointer to add to the build process.
     ///
-    pub fn create(builder: *Builder, target: CrossTarget, files: []const []const u8, out_file_path: []const u8) *RamdiskStep {
+    pub fn create(builder: *std.Build, target: CrossTarget, files: []const []const u8, out_file_path: []const u8) *RamdiskStep {
         const ramdisk_step = builder.allocator.create(RamdiskStep) catch unreachable;
         ramdisk_step.* = .{
             .step = Step.init(.custom, builder.fmt("Ramdisk", .{}), builder.allocator, make),

mkfat32.zig

@@ -311,13 +311,13 @@ pub const Fat32 = struct {
 
         return switch (image_size) {
             0...35 * 512 - 1 => Error.TooSmall,
-            35 * 512...64 * MB - 1 => @intCast(u8, std.math.max(512, bytes_per_sector) / bytes_per_sector),
+            35 * 512...64 * MB - 1 => @intCast(std.math.max(512, bytes_per_sector) / bytes_per_sector),
-            64 * MB...128 * MB - 1 => @intCast(u8, std.math.max(1024, bytes_per_sector) / bytes_per_sector),
+            64 * MB...128 * MB - 1 => @intCast(std.math.max(1024, bytes_per_sector) / bytes_per_sector),
-            128 * MB...256 * MB - 1 => @intCast(u8, std.math.max(2048, bytes_per_sector) / bytes_per_sector),
+            128 * MB...256 * MB - 1 => @intCast(std.math.max(2048, bytes_per_sector) / bytes_per_sector),
-            256 * MB...8 * GB - 1 => @intCast(u8, std.math.max(4096, bytes_per_sector) / bytes_per_sector),
+            256 * MB...8 * GB - 1 => @intCast(std.math.max(4096, bytes_per_sector) / bytes_per_sector),
-            8 * GB...16 * GB - 1 => @intCast(u8, std.math.max(8192, bytes_per_sector) / bytes_per_sector),
+            8 * GB...16 * GB - 1 => @intCast(std.math.max(8192, bytes_per_sector) / bytes_per_sector),
-            16 * GB...32 * GB - 1 => @intCast(u8, std.math.max(16384, bytes_per_sector) / bytes_per_sector),
+            16 * GB...32 * GB - 1 => @intCast(std.math.max(16384, bytes_per_sector) / bytes_per_sector),
-            32 * GB...2 * TB - 1 => @intCast(u8, std.math.max(32768, bytes_per_sector) / bytes_per_sector),
+            32 * GB...2 * TB - 1 => @intCast(std.math.max(32768, bytes_per_sector) / bytes_per_sector),
             else => Error.TooLarge,
         };
     }
@@ -354,7 +354,7 @@ pub const Fat32 = struct {
     fn createSerialNumber() u32 {
         // TODO: Get the actual date. Currently there is no std lib for human readable date.
         const year = 2020;
-        const month = 09;
+        const month = 9;
         const day = 27;
         const hour = 13;
         const minute = 46;
@@ -541,14 +541,14 @@ pub const Fat32 = struct {
         }
 
         // See: https://board.flatassembler.net/topic.php?t=12680
-        var sectors_per_fat = @intCast(u32, (image_size - getReservedSectors() + (2 * options.cluster_size)) / ((options.cluster_size * (options.sector_size / 4)) + 2));
+        var sectors_per_fat: u8 = @intCast((image_size - getReservedSectors() + (2 * options.cluster_size)) / ((options.cluster_size * (options.sector_size / 4)) + 2));
         // round up sectors
         sectors_per_fat = (sectors_per_fat + options.sector_size - 1) / options.sector_size;
 
         return Header{
             .bytes_per_sector = options.sector_size,
             .sectors_per_cluster = options.cluster_size,
-            .total_sectors = @intCast(u32, @divExact(image_size, options.sector_size)),
+            .total_sectors = @intCast(@divExact(image_size, options.sector_size)),
             .sectors_per_fat = sectors_per_fat,
             .serial_number = createSerialNumber(),
             .volume_label = options.volume_name,

src/kernel/arch/x86/arch.zig

@@ -530,8 +530,8 @@ pub fn initKeyboard(allocator: Allocator) Allocator.Error!*Keyboard {
 }
 
 ///
-/// Initialise a stack used for creating a task.
+/// Initialise a stack and vmm payload used for creating a task.
-/// Currently only support fn () noreturn functions for the entry point.
+/// Currently only supports fn () noreturn functions for the entry point.
 ///
 /// Arguments:
 ///     IN task: *Task           - The task to be initialised. The function will only modify whatever
@@ -540,22 +540,24 @@ pub fn initKeyboard(allocator: Allocator) Allocator.Error!*Keyboard {
 ///     IN entry_point: usize    - The pointer to the entry point of the function. Functions only
 ///                                supported is fn () noreturn
 ///     IN allocator: Allocator - The allocator use for allocating a stack.
+///     IN set_up_stack: bool   - Set up the kernel and user stacks (register values, PC etc.) for task entry
 ///
 /// Error: Allocator.Error
 ///     OutOfMemory - Unable to allocate space for the stack.
 ///
-pub fn initTask(task: *Task, entry_point: usize, allocator: Allocator) Allocator.Error!void {
+pub fn initTask(task: *Task, entry_point: usize, allocator: Allocator, set_up_stack: bool) Allocator.Error!void {
+    // TODO Will need to add the exit point
+    // Set up everything as a kernel task
+    task.vmm.payload = &paging.kernel_directory;
+
+    var stack = &task.kernel_stack;
+    const kernel_stack_bottom = if (!set_up_stack) 0 else if (task.kernel) task.kernel_stack.len - 18 else task.kernel_stack.len - 20;
+    if (set_up_stack) {
         const data_offset = if (task.kernel) gdt.KERNEL_DATA_OFFSET else gdt.USER_DATA_OFFSET | 0b11;
         // Setting the bottom two bits of the code offset designates that this is a ring 3 task
         const code_offset = if (task.kernel) gdt.KERNEL_CODE_OFFSET else gdt.USER_CODE_OFFSET | 0b11;
         // Ring switches push and pop two extra values on interrupt: user_esp and user_ss
-    const kernel_stack_bottom = if (task.kernel) task.kernel_stack.len - 18 else task.kernel_stack.len - 20;
 
-    var stack = &task.kernel_stack;
-
-    // TODO Will need to add the exit point
-    // Set up everything as a kernel task
-    task.vmm.payload = &paging.kernel_directory;
         stack.*[kernel_stack_bottom] = mem.virtToPhys(@ptrToInt(&paging.kernel_directory));
         stack.*[kernel_stack_bottom + 1] = data_offset; // gs
         stack.*[kernel_stack_bottom + 2] = data_offset; // fs
@@ -579,23 +581,25 @@ pub fn initTask(task: *Task, entry_point: usize, allocator: Allocator) Allocator
         stack.*[kernel_stack_bottom + 15] = entry_point; // eip
         stack.*[kernel_stack_bottom + 16] = code_offset; // cs
         stack.*[kernel_stack_bottom + 17] = 0x202; // eflags
-
         if (!task.kernel) {
             // Put the extra values on the kernel stack needed when chaning privilege levels
             stack.*[kernel_stack_bottom + 18] = @ptrToInt(&task.user_stack[task.user_stack.len - 1]); // user_esp
             stack.*[kernel_stack_bottom + 19] = data_offset; // user_ss
+        }
+        task.stack_pointer = @ptrToInt(&stack.*[kernel_stack_bottom]);
+    }
 
-        if (!builtin.is_test) {
+    if (!task.kernel and !builtin.is_test) {
         // Create a new page directory for the user task by mirroring the kernel directory
         // We need kernel mem mapped so we don't get a page fault when entering kernel code from an interrupt
         task.vmm.payload = &(try allocator.allocAdvanced(paging.Directory, paging.PAGE_SIZE_4KB, 1, .exact))[0];
         task.vmm.payload.* = paging.kernel_directory.copy();
+        if (set_up_stack) {
             stack.*[kernel_stack_bottom] = vmm.kernel_vmm.virtToPhys(@ptrToInt(task.vmm.payload)) catch |e| {
                 panic(@errorReturnTrace(), "Failed to get the physical address of the user task's page directory: {}\n", .{e});
             };
         }
     }
-    task.stack_pointer = @ptrToInt(&stack.*[kernel_stack_bottom]);
 }
 
 ///

src/kernel/filesystem/vfs.zig

@@ -211,13 +211,8 @@ pub const DirNode = struct {
 
     /// See the documentation for FileSystem.Open
     pub fn open(self: *const DirNode, name: []const u8, flags: OpenFlags, args: OpenArgs) (Allocator.Error || Error)!*Node {
-        var fs = self.fs;
+        var node = self.mount orelse self;
-        var node = self;
+        return node.fs.open(node.fs, node, name, flags, args);
-        if (self.mount) |mnt| {
-            fs = mnt.fs;
-            node = mnt;
-        }
-        return fs.open(fs, node, name, flags, args);
     }
 
     /// See the documentation for FileSystem.Close
@@ -426,6 +421,20 @@ pub fn open(path: []const u8, follow_symlinks: bool, flags: OpenFlags, args: Ope
     return try traversePath(path, follow_symlinks, flags, args);
 }
 
+///
+/// Close a node.
+///
+/// Arguments:
+///     IN node: Node - The node to close
+///
+pub fn close(node: Node) void {
+    switch (node) {
+        .Dir => |d| d.close(),
+        .File => |f| f.close(),
+        .Symlink => |s| s.close(),
+    }
+}
+
 ///
 /// Open a file at a path.
 ///
@@ -592,7 +601,7 @@ const TestFS = struct {
 
     const Self = @This();
 
-    fn deinit(self: *@This()) void {
+    pub fn deinit(self: *@This()) void {
         self.tree.deinit(self.allocator);
         self.allocator.destroy(self.fs);
     }
@@ -718,7 +727,7 @@ const TestFS = struct {
     }
 };
 
-fn testInitFs(allocator: Allocator) !*TestFS {
+pub fn testInitFs(allocator: Allocator) !*TestFS {
     const fs = try allocator.create(FileSystem);
     var testfs = try allocator.create(TestFS);
     var root_node = try allocator.create(Node);

src/kernel/kmain.zig

@@ -17,6 +17,7 @@ const scheduler = @import("scheduler.zig");
 const vfs = @import("filesystem/vfs.zig");
 const initrd = @import("filesystem/initrd.zig");
 const keyboard = @import("keyboard.zig");
+const syscalls = @import("syscalls.zig");
 const Allocator = std.mem.Allocator;
 
 comptime {
@@ -96,6 +97,7 @@ export fn kmain(boot_payload: arch.BootPayload) void {
         panic_root.panic(@errorReturnTrace(), "Failed to initialise kernel heap: {}\n", .{e});
     };
 
+    syscalls.init(kernel_heap.allocator());
     tty.init(kernel_heap.allocator(), boot_payload);
     var arch_kb = keyboard.init(fixed_allocator.allocator()) catch |e| {
         panic_root.panic(@errorReturnTrace(), "Failed to inititalise keyboard: {}\n", .{e});
@@ -144,7 +146,7 @@ export fn kmain(boot_payload: arch.BootPayload) void {
     kmain_log.info("Creating init2\n", .{});
 
     // Create a init2 task
-    var stage2_task = task.Task.create(@ptrToInt(initStage2), true, kernel_vmm, kernel_heap.allocator()) catch |e| {
+    var stage2_task = task.Task.create(@ptrToInt(initStage2), true, kernel_vmm, kernel_heap.allocator(), true) catch |e| {
         panic_root.panic(@errorReturnTrace(), "Failed to create init stage 2 task: {}\n", .{e});
     };
     scheduler.scheduleTask(stage2_task, kernel_heap.allocator()) catch |e| {

src/kernel/scheduler.zig

@@ -27,7 +27,7 @@ extern var KERNEL_STACK_START: []u32;
 extern var KERNEL_STACK_END: []u32;
 
 /// The current task running
-var current_task: *Task = undefined;
+pub var current_task: *Task = undefined;
 
 /// Array list of all runnable tasks
 var tasks: TailQueue(*Task) = undefined;
@@ -137,15 +137,13 @@ pub fn init(allocator: Allocator, mem_profile: *const mem.MemProfile) Allocator.
     // Init the task list for round robin
     tasks = TailQueue(*Task){};
 
-    // Set up the init task to continue execution
+    // Set up the init task to continue execution.
-    current_task = try allocator.create(Task);
+    // The kernel stack will point to the stack section rather than the heap
+    current_task = try Task.create(0, true, &vmm.kernel_vmm, allocator, false);
     errdefer allocator.destroy(current_task);
-    // PID 0
+
-    current_task.pid = 0;
     const kernel_stack_size = @ptrToInt(&KERNEL_STACK_END) - @ptrToInt(&KERNEL_STACK_START);
     current_task.kernel_stack = @intToPtr([*]u32, @ptrToInt(&KERNEL_STACK_START))[0..kernel_stack_size];
-    current_task.user_stack = &[_]usize{};
-    current_task.kernel = true;
     // ESP will be saved on next schedule
 
     // Run the runtime tests here
@@ -155,7 +153,7 @@ pub fn init(allocator: Allocator, mem_profile: *const mem.MemProfile) Allocator.
     }
 
     // Create the idle task when there are no more tasks left
-    var idle_task = try Task.create(@ptrToInt(idle), true, &vmm.kernel_vmm, allocator);
+    var idle_task = try Task.create(@ptrToInt(idle), true, &vmm.kernel_vmm, allocator, true);
     errdefer idle_task.destroy(allocator);
 
     try scheduleTask(idle_task, allocator);
@@ -195,21 +193,21 @@ test "pickNextTask" {
     tasks = TailQueue(*Task){};
 
     // Set up a current task
-    var first = try allocator.create(Task);
+    var first = try Task.create(0, true, &vmm.kernel_vmm, allocator, false);
     // We use an intermediary variable to avoid a double-free.
     // Deferring freeing current_task will free whatever current_task points to at the end
-    defer allocator.destroy(first);
+    defer first.destroy(allocator);
     current_task = first;
     current_task.pid = 0;
     current_task.kernel_stack = @intToPtr([*]u32, @ptrToInt(&KERNEL_STACK_START))[0..4096];
     current_task.stack_pointer = @ptrToInt(&KERNEL_STACK_START);
 
     // Create two tasks and schedule them
-    var test_fn1_task = try Task.create(@ptrToInt(test_fn1), true, undefined, allocator);
+    var test_fn1_task = try Task.create(@ptrToInt(test_fn1), true, undefined, allocator, true);
     defer test_fn1_task.destroy(allocator);
     try scheduleTask(test_fn1_task, allocator);
 
-    var test_fn2_task = try Task.create(@ptrToInt(test_fn2), true, undefined, allocator);
+    var test_fn2_task = try Task.create(@ptrToInt(test_fn2), true, undefined, allocator, true);
     defer test_fn2_task.destroy(allocator);
     try scheduleTask(test_fn2_task, allocator);
 
@@ -254,7 +252,7 @@ test "createNewTask add new task" {
     // Init the task list
     tasks = TailQueue(*Task){};
 
-    var test_fn1_task = try Task.create(@ptrToInt(test_fn1), true, undefined, allocator);
+    var test_fn1_task = try Task.create(@ptrToInt(test_fn1), true, undefined, allocator, true);
     defer test_fn1_task.destroy(allocator);
     try scheduleTask(test_fn1_task, allocator);
 
@@ -309,7 +307,7 @@ fn rt_variable_preserved(allocator: Allocator) void {
     defer allocator.destroy(is_set);
     is_set.* = true;
 
-    var test_task = Task.create(@ptrToInt(task_function), true, &vmm.kernel_vmm, allocator) catch |e| panic(@errorReturnTrace(), "Failed to create task in rt_variable_preserved: {}\n", .{e});
+    var test_task = Task.create(@ptrToInt(task_function), true, &vmm.kernel_vmm, allocator, true) catch |e| panic(@errorReturnTrace(), "Failed to create task in rt_variable_preserved: {}\n", .{e});
     scheduleTask(test_task, allocator) catch |e| panic(@errorReturnTrace(), "Failed to schedule a task in rt_variable_preserved: {}\n", .{e});
     // TODO: Need to add the ability to remove tasks
 

src/kernel/syscalls.zig

@@ -1,14 +1,99 @@
 const std = @import("std");
+const testing = std.testing;
+const is_test = @import("builtin").is_test;
 const scheduler = @import("scheduler.zig");
 const panic = @import("panic.zig").panic;
 const log = std.log.scoped(.syscalls);
 const arch = @import("arch.zig").internals;
+const vfs = @import("filesystem/vfs.zig");
+const task = @import("task.zig");
+const vmm = @import("vmm.zig");
+const mem = @import("mem.zig");
+const pmm = @import("pmm.zig");
+const bitmap = @import("bitmap.zig");
 
-/// A compilation of all errors that syscall handlers could return.
+var allocator: std.mem.Allocator = undefined;
-pub const Error = error{OutOfMemory};
+
+/// The maximum amount of data to allocate when copying user memory into kernel memory
+pub const USER_MAX_DATA_LEN = 16 * 1024;
+
+pub const Error = error{ NoMoreFSHandles, TooBig, NotAFile };
 
 /// All implemented syscalls
 pub const Syscall = enum {
+    /// Open a new vfs node
+    ///
+    /// Arguments:
+    ///     path_ptr: usize - The user/kernel pointer to the file path to open
+    ///     path_len: usize - The length of the file path
+    ///     flags: usize    - The flag specifying what to do with the opened node. Use the integer value of vfs.OpenFlags
+    ///     args: usize     - The user/kernel pointer to the structure holding the vfs.OpenArgs
+    ///     ignored: usize  - Ignored
+    ///
+    /// Return: usize
+    ///     The handle for the opened vfs node
+    ///
+    /// Error:
+    ///     NoMoreFSHandles     - The task has reached the maximum number of allowed vfs handles
+    ///     OutOfMemory         - There wasn't enough kernel (heap or VMM) memory left to fulfill the request.
+    ///     TooBig              - The path length is greater than allowed
+    ///     InvalidAddress      - A pointer that the user task passed is invalid (not mapped, out of bounds etc.)
+    ///     InvalidFlags        - The flags provided don't correspond to a vfs.OpenFlags value
+    ///     Refer to vfs.Error for details on what causes vfs errors
+    ///
+    Open,
+
+    /// Read data from an open vfs file
+    ///
+    /// Arguments:
+    ///     node_handle: usize  - The file handle returned from the open syscall
+    ///     buff_ptr: usize `   - The user/kernel address of the buffer to put the read data in
+    ///     buff_len: usize     - The size of the buffer
+    ///     ignored1: usize     - Ignored
+    ///     ignored2: usize     - Ignored
+    ///
+    /// Return: usize
+    ///     The number of bytes read and put into the buffer
+    ///
+    /// Error:
+    ///     OutOfBounds         - The node handle is outside of the maximum per process
+    ///     TooBig              - The buffer is bigger than what a user process is allowed to give the kernel
+    ///     NotAFile            - The handle does not correspond to a file
+    ///     Refer to vfs.FileNode.read and vmm.VirtualMemoryManager.copyData for details on what causes other errors
+    ///
+    Read,
+    /// Write data from to open vfs file
+    ///
+    /// Arguments:
+    ///     node_handle: usize  - The file handle returned from the open syscall
+    ///     buff_ptr: usize `   - The user/kernel address of the buffer containing the data to write
+    ///     buff_len: usize     - The size of the buffer
+    ///     ignored1: usize     - Ignored
+    ///     ignored2: usize     - Ignored
+    ///
+    /// Return: usize
+    ///     The number of bytes written
+    ///
+    /// Error:
+    ///     OutOfBounds         - The node handle is outside of the maximum per process
+    ///     TooBig              - The buffer is bigger than what a user process is allowed to give the kernel
+    ///     NotAFile            - The handle does not correspond to a file
+    ///     Refer to vfs.FileNode.read and vmm.VirtualMemoryManager.copyData for details on what causes other errors
+    ///
+    Write,
+    ///
+    /// Close an open vfs node. What it means to "close" depends on the underlying file system, but often it will cause the file to be committed to disk or for a network socket to be closed
+    ///
+    /// Arguments:
+    ///     node_handle: usize  - The handle to close
+    ///     ignored1..4: usize  - Ignored
+    ///
+    /// Return: void
+    ///
+    /// Error:
+    ///     OutOfBounds         - The node handle is outside of the maximum per process
+    ///     NotOpened           - The node handle hasn't been opened
+    Close,
     Test1,
     Test2,
     Test3,
@@ -24,6 +109,10 @@ pub const Syscall = enum {
     ///
     fn getHandler(self: @This()) Handler {
         return switch (self) {
+            .Open => handleOpen,
+            .Read => handleRead,
+            .Write => handleWrite,
+            .Close => handleClose,
             .Test1 => handleTest1,
             .Test2 => handleTest2,
             .Test3 => handleTest3,
@@ -42,21 +131,26 @@ pub const Syscall = enum {
     pub fn isTest(self: @This()) bool {
         return switch (self) {
             .Test1, .Test2, .Test3 => true,
+            else => false,
         };
     }
 };
 
 /// A function that can handle a syscall and return a result or an error
-pub const Handler = fn (ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) Error!usize;
+pub const Handler = fn (ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) anyerror!usize;
+
+pub fn init(alloc: std.mem.Allocator) void {
+    allocator = alloc;
+}
 
 ///
-/// Convert an error code to an instance of Error. The conversion must be synchronised with toErrorCode
+/// Convert an error code to an instance of anyerror. The conversion must be synchronised with toErrorCode
 /// Passing an error code that does not correspond to an error results in safety-protected undefined behaviour
 ///
 /// Arguments:
 ///     IN code: u16 - The erorr code to convert
 ///
-/// Return: Error
+/// Return: anyerror
 ///     The error corresponding to the error code
 ///
 pub fn fromErrorCode(code: u16) anyerror {
@@ -64,10 +158,10 @@ pub fn fromErrorCode(code: u16) anyerror {
 }
 
 ///
-/// Convert an instance of Error to an error code. The conversion must be synchronised with fromErrorCode
+/// Convert an instance of anyerror to an error code. The conversion must be synchronised with fromErrorCode
 ///
 /// Arguments:
-///     IN err: Error - The erorr to convert
+///     IN err: anyerror - The erorr to convert
 ///
 /// Return: u16
 ///     The error code corresponding to the error
@@ -86,14 +180,223 @@ pub fn toErrorCode(err: anyerror) u16 {
 /// Return: usize
 ///     The syscall result
 ///
-/// Error: Error
+/// Error: anyerror
 ///     The error raised by the handler
 ///
-pub fn handle(syscall: Syscall, ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) Error!usize {
+pub fn handle(syscall: Syscall, ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) anyerror!usize {
     return try syscall.getHandler()(ctx, arg1, arg2, arg3, arg4, arg5);
 }
 
-pub fn handleTest1(ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) Error!usize {
+///
+/// Get a slice containing the data at an address and length. If the current task is a kernel task then a simple pointer to slice conversion is performed,
+/// otherwise the slice is allocated on the heap and the data is copied in from user space.
+///
+/// Arguments:
+///     IN ptr: usize - The slice's address
+///     IN len: usize - The number of bytes
+///
+/// Error: Error || Allocator.Error || VmmError || BitmapError
+///     OutOfMemory - There wasn't enough kernel (heap or VMM) memory left to fulfill the request.
+///     TooBig - The user task requested to have too much data copied
+///     NotAllocated - The pointer hasn't been mapped by the task
+///     OutOfBounds - The pointer and length is out of bounds of the task's VMM
+///
+/// Return: []u8
+///     The slice of data. Will be stack-allocated if the current task is kernel-level, otherwise will be heap-allocated
+///
+fn getData(ptr: usize, len: usize) (Error || std.mem.Allocator.Error || vmm.VmmError || bitmap.BitmapError)![]u8 {
+    if (scheduler.current_task.kernel) {
+        if (try vmm.kernel_vmm.isSet(ptr)) {
+            return @intToPtr([*]u8, ptr)[0..len];
+        } else {
+            return error.NotAllocated;
+        }
+    } else {
+        if (len > USER_MAX_DATA_LEN) {
+            return Error.TooBig;
+        }
+        var buff = try allocator.alloc(u8, len);
+        errdefer allocator.free(buff);
+        try vmm.kernel_vmm.copyData(scheduler.current_task.vmm, false, buff, ptr);
+        return buff;
+    }
+}
+
+/// Open a new vfs node
+///
+/// Arguments:
+///     path_ptr: usize - The user/kernel pointer to the file path to open
+///     path_len: usize - The length of the file path
+///     flags: usize    - The flag specifying what to do with the opened node. Use the integer value of vfs.OpenFlags
+///     args: usize     - The user/kernel pointer to the structure holding the vfs.OpenArgs
+///     ignored: usize  - Ignored
+///
+/// Return: usize
+///     The handle for the opened vfs node
+///
+/// Error:
+///     NoMoreFSHandles     - The task has reached the maximum number of allowed vfs handles
+///     OutOfMemory         - There wasn't enough kernel (heap or VMM) memory left to fulfill the request.
+///     TooBig              - The path length is greater than allowed
+///     InvalidAddress      - A pointer that the user task passed is invalid (not mapped, out of bounds etc.)
+///     InvalidFlags        - The flags provided don't correspond to a vfs.OpenFlags value
+///     Refer to vfs.Error for details on what causes vfs errors
+///
+fn handleOpen(ctx: *const arch.CpuState, path_ptr: usize, path_len: usize, flags: usize, args: usize, ignored: usize) anyerror!usize {
+    _ = ctx;
+    _ = ignored;
+    const current_task = scheduler.current_task;
+    if (!current_task.hasFreeVFSHandle()) {
+        return Error.NoMoreFSHandles;
+    }
+
+    // Fetch the open arguments from user/kernel memory
+    var open_args: vfs.OpenArgs = if (args == 0) .{} else blk: {
+        const data = try getData(args, @sizeOf(vfs.OpenArgs));
+        defer if (!current_task.kernel) allocator.free(data);
+        break :blk std.mem.bytesAsValue(vfs.OpenArgs, data[0..@sizeOf(vfs.OpenArgs)]).*;
+    };
+    // The symlink target could refer to a location in user memory so convert that too
+    if (open_args.symlink_target) |target| {
+        open_args.symlink_target = try getData(@ptrToInt(target.ptr), target.len);
+    }
+    defer if (!current_task.kernel) if (open_args.symlink_target) |target| allocator.free(target);
+
+    const open_flags = std.meta.intToEnum(vfs.OpenFlags, flags) catch return error.InvalidFlags;
+    const path = try getData(path_ptr, path_len);
+    defer if (!current_task.kernel) allocator.free(path);
+
+    const node = try vfs.open(path, true, open_flags, open_args);
+    errdefer vfs.close(node.*);
+    return (try current_task.addVFSHandle(node)) orelse panic(null, "Failed to add a VFS handle to current_task\n", .{});
+}
+
+/// Read data from an open vfs file
+///
+/// Arguments:
+///     node_handle: usize  - The file handle returned from the open syscall
+///     buff_ptr: usize `   - The user/kernel address of the buffer to put the read data in
+///     buff_len: usize     - The size of the buffer
+///     ignored1: usize     - Ignored
+///     ignored2: usize     - Ignored
+///
+/// Return: usize
+///     The number of bytes read and put into the buffer
+///
+/// Error:
+///     OutOfBounds         - The node handle is outside of the maximum per process
+///     TooBig              - The buffer is bigger than what a user process is allowed to give the kernel
+///     NotAFile            - The handle does not correspond to a file
+///     NotOpened           - The handle doesn't correspond to an opened file
+///     Refer to vfs.FileNode.read and vmm.VirtualMemoryManager.copyData for details on what causes other errors
+///
+fn handleRead(ctx: *const arch.CpuState, node_handle: usize, buff_ptr: usize, buff_len: usize, ignored1: usize, ignored2: usize) anyerror!usize {
+    _ = ctx;
+    _ = ignored1;
+    _ = ignored2;
+    if (node_handle >= task.VFS_HANDLES_PER_PROCESS)
+        return error.OutOfBounds;
+    const real_handle = @intCast(task.Handle, node_handle);
+    if (buff_len > USER_MAX_DATA_LEN) {
+        return Error.TooBig;
+    }
+
+    const current_task = scheduler.current_task;
+    const node_opt = current_task.getVFSHandle(real_handle) catch panic(@errorReturnTrace(), "Failed to get VFS node for handle {}\n", .{real_handle});
+    if (node_opt) |node| {
+        const file = switch (node.*) {
+            .File => |*f| f,
+            else => return error.NotAFile,
+        };
+        var buff = if (current_task.kernel) @intToPtr([*]u8, buff_ptr)[0..buff_len] else try allocator.alloc(u8, buff_len);
+        defer if (!current_task.kernel) allocator.free(buff);
+
+        const bytes_read = try file.read(buff);
+        // TODO: A more performant method would be mapping in the user memory and using that directly. Then we wouldn't need to allocate or copy the buffer
+        if (!current_task.kernel) try vmm.kernel_vmm.copyData(current_task.vmm, true, buff, buff_ptr);
+        return bytes_read;
+    }
+
+    return error.NotOpened;
+}
+
+/// Write data from to open vfs file
+///
+/// Arguments:
+///     node_handle: usize  - The file handle returned from the open syscall
+///     buff_ptr: usize `   - The user/kernel address of the buffer containing the data to write
+///     buff_len: usize     - The size of the buffer
+///     ignored1: usize     - Ignored
+///     ignored2: usize     - Ignored
+///
+/// Return: usize
+///     The number of bytes written
+///
+/// Error:
+///     OutOfBounds         - The node handle is outside of the maximum per process
+///     TooBig              - The buffer is bigger than what a user process is allowed to give the kernel
+///     NotAFile            - The handle does not correspond to a file
+///     NotOpened           - The handle doesn't correspond to an opened file
+///     Refer to vfs.FileNode.read and vmm.VirtualMemoryManager.copyData for details on what causes other errors
+///
+fn handleWrite(ctx: *const arch.CpuState, node_handle: usize, buff_ptr: usize, buff_len: usize, ignored1: usize, ignored2: usize) anyerror!usize {
+    _ = ctx;
+    _ = ignored1;
+    _ = ignored2;
+    if (node_handle >= task.VFS_HANDLES_PER_PROCESS)
+        return error.OutOfBounds;
+    const real_handle = @intCast(task.Handle, node_handle);
+
+    const current_task = scheduler.current_task;
+    const node_opt = current_task.getVFSHandle(real_handle) catch panic(@errorReturnTrace(), "Failed to get VFS node for handle {}\n", .{real_handle});
+    if (node_opt) |node| {
+        const file = switch (node.*) {
+            .File => |*f| f,
+            else => return error.NotAFile,
+        };
+
+        // TODO: A more performant method would be mapping in the user memory and using that directly. Then we wouldn't need to allocate or copy the buffer
+        var buff = try getData(buff_ptr, buff_len);
+        defer if (!current_task.kernel) allocator.free(buff);
+        return try file.write(buff);
+    }
+
+    return error.NotOpened;
+}
+
+///
+/// Close an open vfs node. What it means to "close" depends on the underlying file system, but often it will cause the file to be committed to disk or for a network socket to be closed
+///
+/// Arguments:
+///     node_handle: usize  - The handle to close
+///     ignored1..4: usize  - Ignored
+///
+/// Return: void
+///
+/// Error:
+///     OutOfBounds         - The node handle is outside of the maximum per process
+///     NotOpened           - The node handle hasn't been opened
+fn handleClose(ctx: *const arch.CpuState, node_handle: usize, ignored1: usize, ignored2: usize, ignored3: usize, ignored4: usize) anyerror!usize {
+    _ = ctx;
+    _ = ignored1;
+    _ = ignored2;
+    _ = ignored3;
+    _ = ignored4;
+    if (node_handle >= task.VFS_HANDLES_PER_PROCESS)
+        return error.OutOfBounds;
+    const real_handle = @intCast(task.Handle, node_handle);
+    const current_task = scheduler.current_task;
+    const node_opt = current_task.getVFSHandle(real_handle) catch panic(@errorReturnTrace(), "Failed to get VFS node for handle {}\n", .{real_handle});
+    if (node_opt) |node| {
+        current_task.clearVFSHandle(real_handle) catch |e| return switch (e) {
+            error.VFSHandleNotSet, error.OutOfBounds => error.NotOpened,
+        };
+        vfs.close(node.*);
+    }
+    return error.NotOpened;
+}
+
+pub fn handleTest1(ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) anyerror!usize {
     // Suppress unused variable warnings
     _ = ctx;
     _ = arg1;
@@ -104,12 +407,12 @@ pub fn handleTest1(ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: us
     return 0;
 }
 
-pub fn handleTest2(ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) Error!usize {
+pub fn handleTest2(ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) anyerror!usize {
     _ = ctx;
     return arg1 + arg2 + arg3 + arg4 + arg5;
 }
 
-pub fn handleTest3(ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) Error!usize {
+pub fn handleTest3(ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) anyerror!usize {
     // Suppress unused variable warnings
     _ = ctx;
     _ = arg1;
@@ -117,18 +420,351 @@ pub fn handleTest3(ctx: *const arch.CpuState, arg1: usize, arg2: usize, arg3: us
     _ = arg3;
     _ = arg4;
     _ = arg5;
-    return std.mem.Allocator.Error.OutOfMemory;
+    return error.OutOfMemory;
+}
+
+fn testInitMem(comptime num_vmm_entries: usize, alloc: std.mem.Allocator, map_all: bool) !std.heap.FixedBufferAllocator {
+    // handleOpen requires that the name passed is mapped in the VMM
+    // Allocate them within a buffer so we know the start and end address to give to the VMM
+    var buffer = try alloc.alloc(u8, num_vmm_entries * vmm.BLOCK_SIZE);
+    var fixed_buffer_allocator = std.heap.FixedBufferAllocator.init(buffer[0..]);
+
+    vmm.kernel_vmm = try vmm.VirtualMemoryManager(arch.VmmPayload).init(@ptrToInt(fixed_buffer_allocator.buffer.ptr), @ptrToInt(fixed_buffer_allocator.buffer.ptr) + buffer.len, alloc, arch.VMM_MAPPER, arch.KERNEL_VMM_PAYLOAD);
+    // The PMM is required as well
+    const mem_profile = mem.MemProfile{
+        .vaddr_end = undefined,
+        .vaddr_start = undefined,
+        .physaddr_start = undefined,
+        .physaddr_end = undefined,
+        .mem_kb = num_vmm_entries * vmm.BLOCK_SIZE / 1024,
+        .fixed_allocator = undefined,
+        .virtual_reserved = &[_]mem.Map{},
+        .physical_reserved = &[_]mem.Range{},
+        .modules = &[_]mem.Module{},
+    };
+    pmm.init(&mem_profile, alloc);
+    // Set the whole VMM space as mapped so all address within the buffer allocator will be considered valid
+    if (map_all) _ = try vmm.kernel_vmm.alloc(num_vmm_entries, null, .{ .kernel = true, .writable = true, .cachable = true });
+    return fixed_buffer_allocator;
+}
+
+fn testDeinitMem(alloc: std.mem.Allocator, buffer_allocator: std.heap.FixedBufferAllocator) void {
+    alloc.free(buffer_allocator.buffer);
+    vmm.kernel_vmm.deinit();
+    pmm.deinit();
 }
 
 test "getHandler" {
     try std.testing.expectEqual(Syscall.Test1.getHandler(), handleTest1);
     try std.testing.expectEqual(Syscall.Test2.getHandler(), handleTest2);
     try std.testing.expectEqual(Syscall.Test3.getHandler(), handleTest3);
+    try std.testing.expectEqual(Syscall.Open.getHandler(), handleOpen);
+    try std.testing.expectEqual(Syscall.Close.getHandler(), handleClose);
+    try std.testing.expectEqual(Syscall.Read.getHandler(), handleRead);
+    try std.testing.expectEqual(Syscall.Write.getHandler(), handleWrite);
 }
 
 test "handle" {
     const state = arch.CpuState.empty();
     try std.testing.expectEqual(@as(usize, 0), try handle(.Test1, &state, 0, 0, 0, 0, 0));
     try std.testing.expectEqual(@as(usize, 1 + 2 + 3 + 4 + 5), try handle(.Test2, &state, 1, 2, 3, 4, 5));
-    try std.testing.expectError(Error.OutOfMemory, handle(.Test3, &state, 0, 0, 0, 0, 0));
+    try std.testing.expectError(error.OutOfMemory, handle(.Test3, &state, 0, 0, 0, 0, 0));
+}
+
+test "handleOpen" {
+    allocator = std.testing.allocator;
+    var testfs = try vfs.testInitFs(allocator);
+    defer allocator.destroy(testfs);
+    defer testfs.deinit();
+
+    testfs.instance = 1;
+    try vfs.setRoot(testfs.tree.val);
+
+    var fixed_buffer_allocator = try testInitMem(1, allocator, true);
+    var buffer_allocator = fixed_buffer_allocator.allocator();
+    defer testDeinitMem(allocator, fixed_buffer_allocator);
+
+    scheduler.current_task = try task.Task.create(0, true, undefined, allocator, true);
+    defer scheduler.current_task.destroy(allocator);
+    var current_task = scheduler.current_task;
+
+    const empty = arch.CpuState.empty();
+
+    // Creating a file
+    var name1 = try buffer_allocator.dupe(u8, "/abc.txt");
+    var test_handle = @intCast(task.Handle, try handleOpen(&empty, @ptrToInt(name1.ptr), name1.len, @enumToInt(vfs.OpenFlags.CREATE_FILE), 0, undefined));
+    var test_node = (try current_task.getVFSHandle(test_handle)).?;
+    try testing.expectEqual(testfs.tree.children.items.len, 1);
+    var tree = testfs.tree.children.items[0];
+    try testing.expect(tree.val.isFile() and test_node.isFile());
+    try testing.expectEqual(&test_node.File, &tree.val.File);
+    try testing.expect(std.mem.eql(u8, tree.name, "abc.txt"));
+    try testing.expectEqual(tree.data, null);
+    try testing.expectEqual(tree.children.items.len, 0);
+
+    // Creating a dir
+    var name2 = try buffer_allocator.dupe(u8, "/def");
+    test_handle = @intCast(task.Handle, try handleOpen(&empty, @ptrToInt(name2.ptr), name2.len, @enumToInt(vfs.OpenFlags.CREATE_DIR), 0, undefined));
+    test_node = (try current_task.getVFSHandle(test_handle)).?;
+    try testing.expectEqual(testfs.tree.children.items.len, 2);
+    tree = testfs.tree.children.items[1];
+    try testing.expect(tree.val.isDir() and test_node.isDir());
+    try testing.expectEqual(&test_node.Dir, &tree.val.Dir);
+    try testing.expect(std.mem.eql(u8, tree.name, "def"));
+    try testing.expectEqual(tree.data, null);
+    try testing.expectEqual(tree.children.items.len, 0);
+
+    // Creating a file under a new dir
+    var name3 = try buffer_allocator.dupe(u8, "/def/ghi.zig");
+    test_handle = @intCast(task.Handle, try handleOpen(&empty, @ptrToInt(name3.ptr), name3.len, @enumToInt(vfs.OpenFlags.CREATE_FILE), 0, undefined));
+    test_node = (try current_task.getVFSHandle(test_handle)).?;
+    try testing.expectEqual(testfs.tree.children.items[1].children.items.len, 1);
+    tree = testfs.tree.children.items[1].children.items[0];
+    try testing.expect(tree.val.isFile() and test_node.isFile());
+    try testing.expectEqual(&test_node.File, &tree.val.File);
+    try testing.expect(std.mem.eql(u8, tree.name, "ghi.zig"));
+    try testing.expectEqual(tree.data, null);
+    try testing.expectEqual(tree.children.items.len, 0);
+
+    // Opening an existing file
+    test_handle = @intCast(task.Handle, try handleOpen(&empty, @ptrToInt(name3.ptr), name3.len, @enumToInt(vfs.OpenFlags.NO_CREATION), 0, undefined));
+    test_node = (try current_task.getVFSHandle(test_handle)).?;
+    try testing.expectEqual(testfs.tree.children.items[1].children.items.len, 1);
+    try testing.expect(test_node.isFile());
+    try testing.expectEqual(&test_node.File, &tree.val.File);
+}
+
+test "handleRead" {
+    allocator = std.testing.allocator;
+    var testfs = try vfs.testInitFs(allocator);
+    defer allocator.destroy(testfs);
+    defer testfs.deinit();
+
+    testfs.instance = 1;
+    try vfs.setRoot(testfs.tree.val);
+
+    var fixed_buffer_allocator = try testInitMem(1, allocator, true);
+    var buffer_allocator = fixed_buffer_allocator.allocator();
+    defer testDeinitMem(allocator, fixed_buffer_allocator);
+    scheduler.current_task = try task.Task.create(0, true, &vmm.kernel_vmm, allocator, true);
+    defer scheduler.current_task.destroy(allocator);
+    _ = scheduler.current_task;
+
+    const empty = arch.CpuState.empty();
+
+    var test_file_path = try buffer_allocator.dupe(u8, "/foo.txt");
+    var test_file = @intCast(task.Handle, try handleOpen(&empty, @ptrToInt(test_file_path.ptr), test_file_path.len, @enumToInt(vfs.OpenFlags.CREATE_FILE), 0, undefined));
+    var f_data = &testfs.tree.children.items[0].data;
+    var str = "test123";
+    f_data.* = try testing.allocator.dupe(u8, str);
+
+    var buffer: [str.len]u8 = undefined;
+    {
+        const length = try handleRead(&empty, test_file, @ptrToInt(&buffer[0]), buffer.len, 0, undefined);
+        try testing.expect(std.mem.eql(u8, str, buffer[0..length]));
+    }
+
+    {
+        const length = try handleRead(&empty, test_file, @ptrToInt(&buffer[0]), buffer.len + 1, 0, undefined);
+        try testing.expect(std.mem.eql(u8, str, buffer[0..length]));
+    }
+
+    {
+        const length = try handleRead(&empty, test_file, @ptrToInt(&buffer[0]), buffer.len + 3, 0, undefined);
+        try testing.expect(std.mem.eql(u8, str, buffer[0..length]));
+    }
+
+    {
+        const length = try handleRead(&empty, test_file, @ptrToInt(&buffer[0]), buffer.len - 1, 0, undefined);
+        try testing.expect(std.mem.eql(u8, str[0 .. str.len - 1], buffer[0..length]));
+    }
+
+    {
+        const length = try handleRead(&empty, test_file, @ptrToInt(&buffer[0]), 0, 0, undefined);
+        try testing.expect(std.mem.eql(u8, str[0..0], buffer[0..length]));
+    }
+    // Try reading from a symlink
+    var args = try buffer_allocator.create(vfs.OpenArgs);
+    args.* = vfs.OpenArgs{ .symlink_target = test_file_path };
+    var link = try buffer_allocator.dupe(u8, "/link");
+    var test_link = @intCast(task.Handle, try handleOpen(&empty, @ptrToInt(link.ptr), link.len, @enumToInt(vfs.OpenFlags.CREATE_SYMLINK), @ptrToInt(args), undefined));
+    {
+        const length = try handleRead(&empty, test_link, @ptrToInt(&buffer[0]), buffer.len, 0, undefined);
+        try testing.expect(std.mem.eql(u8, str[0..str.len], buffer[0..length]));
+    }
+}
+
+test "handleRead errors" {
+    allocator = std.testing.allocator;
+    var testfs = try vfs.testInitFs(allocator);
+    {
+        defer allocator.destroy(testfs);
+        defer testfs.deinit();
+
+        testfs.instance = 1;
+        try vfs.setRoot(testfs.tree.val);
+
+        const empty = arch.CpuState.empty();
+
+        // The data we pass to handleRead needs to be mapped within the VMM, so we need to know their address
+        // Allocating the data within a fixed buffer allocator is the best way to know the address of the data
+        var fixed_buffer_allocator = try testInitMem(3, allocator, true);
+        var buffer_allocator = fixed_buffer_allocator.allocator();
+        defer testDeinitMem(allocator, fixed_buffer_allocator);
+
+        scheduler.current_task = try task.Task.create(0, true, &vmm.kernel_vmm, allocator, true);
+        defer scheduler.current_task.destroy(allocator);
+
+        // Invalid file handle
+        try testing.expectError(error.OutOfBounds, handleRead(&empty, task.VFS_HANDLES_PER_PROCESS, 0, 0, 0, 0));
+        try testing.expectError(error.OutOfBounds, handleRead(&empty, task.VFS_HANDLES_PER_PROCESS + 1, 0, 0, 0, 0));
+
+        // Unopened file
+        try testing.expectError(error.NotOpened, handleRead(&empty, 0, 0, 0, 0, 0));
+        try testing.expectError(error.NotOpened, handleRead(&empty, 1, 0, 0, 0, 0));
+        try testing.expectError(error.NotOpened, handleRead(&empty, task.VFS_HANDLES_PER_PROCESS - 1, 0, 0, 0, 0));
+
+        // Reading from a dir
+        const name = try buffer_allocator.dupe(u8, "/dir");
+        const node = try handleOpen(&empty, @ptrToInt(name.ptr), name.len, @enumToInt(vfs.OpenFlags.CREATE_DIR), 0, 0);
+        try testing.expectError(error.NotAFile, handleRead(&empty, node, 0, 0, 0, 0));
+
+        // User buffer is too big
+        const name2 = try buffer_allocator.dupe(u8, "/file.txt");
+        const node2 = try handleOpen(&empty, @ptrToInt(name2.ptr), name2.len, @enumToInt(vfs.OpenFlags.CREATE_FILE), 0, 0);
+        scheduler.current_task.kernel = false;
+        try testing.expectError(Error.TooBig, handleRead(&empty, node2, 0, USER_MAX_DATA_LEN + 1, 0, 0));
+    }
+    try testing.expect(!testing.allocator_instance.detectLeaks());
+}
+
+test "handleWrite" {
+    allocator = std.testing.allocator;
+    var testfs = try vfs.testInitFs(allocator);
+    defer allocator.destroy(testfs);
+    defer testfs.deinit();
+
+    testfs.instance = 1;
+    try vfs.setRoot(testfs.tree.val);
+
+    var fixed_buffer_allocator = try testInitMem(1, allocator, true);
+    var buffer_allocator = fixed_buffer_allocator.allocator();
+    defer testDeinitMem(allocator, fixed_buffer_allocator);
+
+    scheduler.current_task = try task.Task.create(0, true, &vmm.kernel_vmm, allocator, true);
+    defer scheduler.current_task.destroy(allocator);
+
+    const empty = arch.CpuState.empty();
+
+    // Open test file
+    const name = try buffer_allocator.dupe(u8, "/abc.txt");
+    const node = try handleOpen(&empty, @ptrToInt(name.ptr), name.len, @enumToInt(vfs.OpenFlags.CREATE_FILE), 0, undefined);
+
+    // Write
+    const data = try buffer_allocator.dupe(u8, "test_data 123");
+    const res = try handleWrite(&empty, node, @ptrToInt(data.ptr), data.len, 0, 0);
+    try testing.expectEqual(res, data.len);
+    try testing.expectEqualSlices(u8, data, testfs.tree.children.items[0].data.?);
+
+    // Write to a file in a folder
+    const name2 = try buffer_allocator.dupe(u8, "/dir");
+    _ = try handleOpen(&empty, @ptrToInt(name2.ptr), name2.len, @enumToInt(vfs.OpenFlags.CREATE_DIR), 0, undefined);
+    const name3 = try buffer_allocator.dupe(u8, "/dir/def.txt");
+    const node3 = try handleOpen(&empty, @ptrToInt(name3.ptr), name3.len, @enumToInt(vfs.OpenFlags.CREATE_FILE), 0, undefined);
+    const data2 = try buffer_allocator.dupe(u8, "some more test data!");
+    const res2 = try handleWrite(&empty, node3, @ptrToInt(data2.ptr), data2.len, 0, 0);
+    try testing.expectEqual(res2, data2.len);
+    try testing.expectEqualSlices(u8, data2, testfs.tree.children.items[1].children.items[0].data.?);
+}
+
+test "handleWrite errors" {
+    allocator = std.testing.allocator;
+    var testfs = try vfs.testInitFs(allocator);
+    {
+        defer allocator.destroy(testfs);
+        defer testfs.deinit();
+
+        testfs.instance = 1;
+        try vfs.setRoot(testfs.tree.val);
+
+        const empty = arch.CpuState.empty();
+
+        // The data we pass to handleWrite needs to be mapped within the VMM, so we need to know their address
+        // Allocating the data within a fixed buffer allocator is the best way to know the address of the data
+        var fixed_buffer_allocator = try testInitMem(3, allocator, true);
+        var buffer_allocator = fixed_buffer_allocator.allocator();
+        defer testDeinitMem(allocator, fixed_buffer_allocator);
+
+        scheduler.current_task = try task.Task.create(0, true, &vmm.kernel_vmm, allocator, true);
+        defer scheduler.current_task.destroy(allocator);
+
+        // Invalid file handle
+        try testing.expectError(error.OutOfBounds, handleWrite(&empty, task.VFS_HANDLES_PER_PROCESS, 0, 0, 0, 0));
+        try testing.expectError(error.OutOfBounds, handleWrite(&empty, task.VFS_HANDLES_PER_PROCESS + 1, 0, 0, 0, 0));
+
+        // Unopened file
+        try testing.expectError(error.NotOpened, handleWrite(&empty, 0, 0, 0, 0, 0));
+        try testing.expectError(error.NotOpened, handleWrite(&empty, 1, 0, 0, 0, 0));
+        try testing.expectError(error.NotOpened, handleWrite(&empty, task.VFS_HANDLES_PER_PROCESS - 1, 0, 0, 0, 0));
+
+        // Writing to a dir
+        const name = try buffer_allocator.dupe(u8, "/dir");
+        const node = try handleOpen(&empty, @ptrToInt(name.ptr), name.len, @enumToInt(vfs.OpenFlags.CREATE_DIR), 0, 0);
+        try testing.expectError(error.NotAFile, handleWrite(&empty, node, 0, 0, 0, 0));
+
+        // User buffer is too big
+        const name2 = try buffer_allocator.dupe(u8, "/file.txt");
+        const node2 = try handleOpen(&empty, @ptrToInt(name2.ptr), name2.len, @enumToInt(vfs.OpenFlags.CREATE_FILE), 0, 0);
+        scheduler.current_task.kernel = false;
+        try testing.expectError(Error.TooBig, handleWrite(&empty, node2, 0, USER_MAX_DATA_LEN + 1, 0, 0));
+    }
+    try testing.expect(!testing.allocator_instance.detectLeaks());
+}
+
+test "handleOpen errors" {
+    allocator = std.testing.allocator;
+    var testfs = try vfs.testInitFs(allocator);
+    {
+        defer allocator.destroy(testfs);
+        defer testfs.deinit();
+
+        testfs.instance = 1;
+        try vfs.setRoot(testfs.tree.val);
+
+        const empty = arch.CpuState.empty();
+
+        // The data we pass to handleOpen needs to be mapped within the VMM, so we need to know their address
+        // Allocating the data within a fixed buffer allocator is the best way to know the address of the data
+        var fixed_buffer_allocator = try testInitMem(3, allocator, false);
+        var buffer_allocator = fixed_buffer_allocator.allocator();
+        defer testDeinitMem(allocator, fixed_buffer_allocator);
+
+        scheduler.current_task = try task.Task.create(0, true, &vmm.kernel_vmm, allocator, true);
+        defer scheduler.current_task.destroy(allocator);
+
+        // Check opening with no free file handles left
+        const free_handles = scheduler.current_task.file_handles.num_free_entries;
+        scheduler.current_task.file_handles.num_free_entries = 0;
+        try testing.expectError(Error.NoMoreFSHandles, handleOpen(&empty, 0, 0, 0, 0, 0));
+        scheduler.current_task.file_handles.num_free_entries = free_handles;
+
+        // Using a path that is too long
+        scheduler.current_task.kernel = false;
+        try testing.expectError(Error.TooBig, handleOpen(&empty, 0, USER_MAX_DATA_LEN + 1, 0, 0, 0));
+
+        // Unallocated user address
+        const test_alloc = try buffer_allocator.alloc(u8, 1);
+        // The kernel VMM and task VMM need to have their buffers mapped, so we'll temporarily use the buffer allocator since it operates within a known address space
+        allocator = buffer_allocator;
+        try testing.expectError(error.NotAllocated, handleOpen(&empty, @ptrToInt(test_alloc.ptr), 1, 0, 0, 0));
+        allocator = std.testing.allocator;
+
+        // Unallocated kernel address
+        scheduler.current_task.kernel = true;
+        try testing.expectError(error.NotAllocated, handleOpen(&empty, @ptrToInt(test_alloc.ptr), 1, 0, 0, 0));
+
+        // Invalid flag enum value
+        try testing.expectError(error.InvalidFlags, handleOpen(&empty, @ptrToInt(test_alloc.ptr), 1, 999, 0, 0));
+    }
+    try testing.expect(!testing.allocator_instance.detectLeaks());
 }

src/kernel/task.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 const expectEqual = std.testing.expectEqual;
 const expectError = std.testing.expectError;
+const expect = std.testing.expect;
 const builtin = @import("builtin");
 const is_test = builtin.is_test;
 const build_options = @import("build_options");
@@ -11,6 +12,7 @@ const pmm = @import("pmm.zig");
 const mem = @import("mem.zig");
 const elf = @import("elf.zig");
 const bitmap = @import("bitmap.zig");
+const vfs = @import("filesystem/vfs.zig");
 const Allocator = std.mem.Allocator;
 const log = std.log.scoped(.task);
 
@@ -18,6 +20,12 @@ const log = std.log.scoped(.task);
 /// as we cannot deallocate this.
 extern var KERNEL_STACK_START: *u32;
 
+/// The number of vfs handles that a process can have
+pub const VFS_HANDLES_PER_PROCESS = std.math.maxInt(Handle);
+
+/// A vfs handle. 65k is probably a good limit for the number of files a task can have open at once so we use u16 as the type
+pub const Handle = u16;
+
 /// The function type for the entry point.
 pub const EntryPoint = usize;
 
@@ -25,18 +33,20 @@ pub const EntryPoint = usize;
 const PidBitmap = bitmap.Bitmap(1024, usize);
 
 /// The list of PIDs that have been allocated.
-var all_pids: PidBitmap = init: {
+var all_pids = PidBitmap.init(1024, null) catch unreachable;
-    var pids = PidBitmap.init(1024, null) catch unreachable;
+
-    // Reserve PID 0 for the init task
+const FileHandleBitmap = bitmap.Bitmap(1024, usize);
-    _ = pids.setFirstFree() orelse unreachable;
-    break :init pids;
-};
 
 /// The default stack size of a task. Currently this is set to a page size.
 pub const STACK_SIZE: u32 = arch.MEMORY_BLOCK_SIZE / @sizeOf(u32);
 
 /// The task control block for storing all the information needed to save and restore a task.
 pub const Task = struct {
+    pub const Error = error{
+        /// The supplied vfs handle hasn't been allocated
+        VFSHandleNotSet,
+    };
+
     const Self = @This();
 
     /// The unique task identifier
@@ -57,6 +67,12 @@ pub const Task = struct {
     /// The virtual memory manager belonging to the task
     vmm: *vmm.VirtualMemoryManager(arch.VmmPayload),
 
+    /// The list of file handles for this process
+    file_handles: FileHandleBitmap,
+
+    /// The mapping between file handles and file nodes
+    file_handle_mapping: std.hash_map.AutoHashMap(Handle, *vfs.Node),
+
     ///
     /// Create a task. This will allocate a PID and the stack. The stack will be set up as a
     /// kernel task. As this is a new task, the stack will need to be initialised with the CPU
@@ -75,15 +91,15 @@ pub const Task = struct {
     ///     OutOfMemory - If there is no more memory to allocate. Any memory or PID allocated will
     ///                   be freed on return.
     ///
-    pub fn create(entry_point: EntryPoint, kernel: bool, task_vmm: *vmm.VirtualMemoryManager(arch.VmmPayload), allocator: Allocator) Allocator.Error!*Task {
+    pub fn create(entry_point: EntryPoint, kernel: bool, task_vmm: *vmm.VirtualMemoryManager(arch.VmmPayload), allocator: Allocator, alloc_kernel_stack: bool) Allocator.Error!*Task {
         var task = try allocator.create(Task);
         errdefer allocator.destroy(task);
 
         const pid = allocatePid();
         errdefer freePid(pid) catch |e| panic(@errorReturnTrace(), "Failed to free task PID in errdefer ({}): {}\n", .{ pid, e });
 
-        var k_stack = try allocator.alloc(usize, STACK_SIZE);
+        var k_stack = if (alloc_kernel_stack) try allocator.alloc(usize, STACK_SIZE) else &[_]usize{};
-        errdefer allocator.free(k_stack);
+        errdefer if (alloc_kernel_stack) allocator.free(k_stack);
 
         var u_stack = if (kernel) &[_]usize{} else try allocator.alloc(usize, STACK_SIZE);
         errdefer if (!kernel) allocator.free(u_stack);
@@ -92,18 +108,20 @@ pub const Task = struct {
             .pid = pid,
             .kernel_stack = k_stack,
             .user_stack = u_stack,
-            .stack_pointer = @ptrToInt(&k_stack[STACK_SIZE - 1]),
+            .stack_pointer = if (!alloc_kernel_stack) 0 else @ptrToInt(&k_stack[STACK_SIZE - 1]),
             .kernel = kernel,
             .vmm = task_vmm,
+            .file_handles = FileHandleBitmap.init(null, null) catch unreachable,
+            .file_handle_mapping = std.hash_map.AutoHashMap(Handle, *vfs.Node).init(allocator),
         };
 
-        try arch.initTask(task, entry_point, allocator);
+        try arch.initTask(task, entry_point, allocator, alloc_kernel_stack);
 
         return task;
     }
 
     pub fn createFromElf(program_elf: elf.Elf, kernel: bool, task_vmm: *vmm.VirtualMemoryManager(arch.VmmPayload), allocator: Allocator) (bitmap.BitmapError || vmm.VmmError || Allocator.Error)!*Task {
-        const task = try create(program_elf.header.entry_address, kernel, task_vmm, allocator);
+        const task = try create(program_elf.header.entry_address, kernel, task_vmm, allocator, true);
         errdefer task.destroy(allocator);
 
         // Iterate over sections
@@ -145,14 +163,103 @@ pub const Task = struct {
         freePid(self.pid) catch |e| panic(@errorReturnTrace(), "Failed to free task's PID ({}): {}\n", .{ self.pid, e });
         // We need to check that the the stack has been allocated as task 0 (init) won't have a
         // stack allocated as this in the linker script
-        if (@ptrToInt(self.kernel_stack.ptr) != @ptrToInt(&KERNEL_STACK_START)) {
+        if (@ptrToInt(self.kernel_stack.ptr) != @ptrToInt(&KERNEL_STACK_START) and self.kernel_stack.len > 0) {
             allocator.free(self.kernel_stack);
         }
         if (!self.kernel) {
             allocator.free(self.user_stack);
         }
+        self.file_handle_mapping.deinit();
         allocator.destroy(self);
     }
+
+    ///
+    /// Get the VFS node associated with a VFS handle.
+    ///
+    /// Arguments:
+    ///     IN self: *Self - The pointer to self.
+    ///     IN handle: Handle - The handle to get the node for. Must have been returned from addVFSHandle.
+    ///
+    /// Return: *vfs.Node
+    ///     The node associated with the handle.
+    ///
+    /// Error: bitmap.BitmapError
+    ///     See Bitmap.
+    ///
+    pub fn getVFSHandle(self: Self, handle: Handle) bitmap.BitmapError!?*vfs.Node {
+        return self.file_handle_mapping.get(handle);
+    }
+
+    ///
+    /// Check if the task has free handles to allocate.
+    ///
+    /// Arguments:
+    ///     IN self: Self - The self.
+    ///
+    /// Return: bool
+    ///     True if there are free handles, else false.
+    ///
+    pub fn hasFreeVFSHandle(self: Self) bool {
+        return self.file_handles.num_free_entries > 0;
+    }
+
+    ///
+    /// Add a handle associated with a node. The node can later be retrieved with getVFSHandle.
+    ///
+    /// Arguments:
+    ///     IN self: *Self - The pointer to self.
+    ///     IN node: *vfs.Node - The node to associate with the returned handle.
+    ///
+    /// Return: Handle
+    ///     The handle now associated with the vfs node.
+    ///
+    /// Error: std.mem.Allocator.Error
+    ///
+    pub fn addVFSHandle(self: *Self, node: *vfs.Node) std.mem.Allocator.Error!?Handle {
+        if (self.file_handles.setFirstFree()) |handle| {
+            const real_handle = @intCast(Handle, handle);
+            try self.file_handle_mapping.put(real_handle, node);
+            return real_handle;
+        }
+        return null;
+    }
+
+    ///
+    /// Check if the task has a certain handle registered.
+    ///
+    /// Arguments:
+    ///     IN self: Self - The self.
+    ///     IN handle: Handle - The handle to check.
+    ///
+    /// Return: bool
+    ///     True if the handle has been registered to this task, else false.
+    ///
+    /// Error: bitmap.BitmapError
+    ///     See Bitmap.
+    ///
+    pub fn hasVFSHandle(self: Self, handle: Handle) bitmap.BitmapError!bool {
+        return self.file_handles.isSet(handle);
+    }
+
+    ///
+    /// Clear a registered handle and de-associate the node from it.
+    ///
+    /// Arguments:
+    ///     IN self: *Self - The pointer to self.
+    ///     IN handle: Handle - The handle to clear. Must have been registered before.
+    ///
+    /// Error: bitmap.BitmapError || Error
+    ///     bitmap.BitmapError.* - See bitmap.BitmapError
+    ///     Error.VFSHandleNotSet - The handle has not previously been registered
+    ///
+    pub fn clearVFSHandle(self: *Self, handle: Handle) (bitmap.BitmapError || Error)!void {
+        if (try self.hasVFSHandle(handle)) {
+            try self.file_handles.clearEntry(handle);
+            _ = self.file_handle_mapping.remove(handle);
+        } else {
+            return Error.VFSHandleNotSet;
+        }
+    }
 };
 
 ///
@@ -192,8 +299,8 @@ test "create out of memory for task" {
     // Set the global allocator
     var fa = FailingAllocator.init(testing_allocator, 0);
 
-    try expectError(error.OutOfMemory, Task.create(@ptrToInt(test_fn1), true, undefined, fa.allocator()));
+    try expectError(error.OutOfMemory, Task.create(@ptrToInt(test_fn1), true, undefined, fa.allocator(), true));
-    try expectError(error.OutOfMemory, Task.create(@ptrToInt(test_fn1), false, undefined, fa.allocator()));
+    try expectError(error.OutOfMemory, Task.create(@ptrToInt(test_fn1), false, undefined, fa.allocator(), true));
 
     // Make sure any memory allocated is freed
     try expectEqual(fa.allocated_bytes, fa.freed_bytes);
@@ -208,8 +315,8 @@ test "create out of memory for stack" {
     // Set the global allocator
     var fa = FailingAllocator.init(testing_allocator, 1);
 
-    try expectError(error.OutOfMemory, Task.create(@ptrToInt(test_fn1), true, undefined, fa.allocator()));
+    try expectError(error.OutOfMemory, Task.create(@ptrToInt(test_fn1), true, undefined, fa.allocator(), true));
-    try expectError(error.OutOfMemory, Task.create(@ptrToInt(test_fn1), false, undefined, fa.allocator()));
+    try expectError(error.OutOfMemory, Task.create(@ptrToInt(test_fn1), false, undefined, fa.allocator(), true));
 
     // Make sure any memory allocated is freed
     try expectEqual(fa.allocated_bytes, fa.freed_bytes);
@@ -221,7 +328,7 @@ test "create out of memory for stack" {
 }
 
 test "create expected setup" {
-    var task = try Task.create(@ptrToInt(test_fn1), true, undefined, std.testing.allocator);
+    var task = try Task.create(@ptrToInt(test_fn1), true, undefined, std.testing.allocator, true);
     defer task.destroy(std.testing.allocator);
 
     // Will allocate the first PID 0
@@ -229,7 +336,7 @@ test "create expected setup" {
     try expectEqual(task.kernel_stack.len, STACK_SIZE);
     try expectEqual(task.user_stack.len, 0);
 
-    var user_task = try Task.create(@ptrToInt(test_fn1), false, undefined, std.testing.allocator);
+    var user_task = try Task.create(@ptrToInt(test_fn1), false, undefined, std.testing.allocator, true);
     defer user_task.destroy(std.testing.allocator);
     try expectEqual(user_task.pid, 1);
     try expectEqual(user_task.user_stack.len, STACK_SIZE);
@@ -241,8 +348,8 @@ test "destroy cleans up" {
     // So if any alloc were not freed, this will fail the test
     var allocator = std.testing.allocator;
 
-    var task = try Task.create(@ptrToInt(test_fn1), true, undefined, allocator);
+    var task = try Task.create(@ptrToInt(test_fn1), true, undefined, allocator, true);
-    var user_task = try Task.create(@ptrToInt(test_fn1), false, undefined, allocator);
+    var user_task = try Task.create(@ptrToInt(test_fn1), false, undefined, allocator, true);
 
     task.destroy(allocator);
     user_task.destroy(allocator);
@@ -254,8 +361,8 @@ test "destroy cleans up" {
 }
 
 test "Multiple create" {
-    var task1 = try Task.create(@ptrToInt(test_fn1), true, undefined, std.testing.allocator);
+    var task1 = try Task.create(@ptrToInt(test_fn1), true, undefined, std.testing.allocator, true);
-    var task2 = try Task.create(@ptrToInt(test_fn1), true, undefined, std.testing.allocator);
+    var task2 = try Task.create(@ptrToInt(test_fn1), true, undefined, std.testing.allocator, true);
 
     try expectEqual(task1.pid, 0);
     try expectEqual(task2.pid, 1);
@@ -271,7 +378,7 @@ test "Multiple create" {
         if (i > 0) try expectEqual(bmp, 0);
     }
 
-    var task3 = try Task.create(@ptrToInt(test_fn1), true, undefined, std.testing.allocator);
+    var task3 = try Task.create(@ptrToInt(test_fn1), true, undefined, std.testing.allocator, true);
 
     try expectEqual(task3.pid, 0);
     try expectEqual(all_pids.bitmaps[0], 3);
@@ -282,7 +389,7 @@ test "Multiple create" {
     task2.destroy(std.testing.allocator);
     task3.destroy(std.testing.allocator);
 
-    var user_task = try Task.create(@ptrToInt(test_fn1), false, undefined, std.testing.allocator);
+    var user_task = try Task.create(@ptrToInt(test_fn1), false, undefined, std.testing.allocator, true);
 
     try expectEqual(user_task.pid, 0);
     try expectEqual(all_pids.bitmaps[0], 1);
@@ -378,3 +485,83 @@ test "createFromElf clean-up" {
     the_elf.section_headers[1].flags |= elf.SECTION_ALLOCATABLE;
     try std.testing.expectError(error.AlreadyAllocated, Task.createFromElf(the_elf, true, &the_vmm, std.testing.allocator));
 }
+
+test "create doesn't allocate kernel stack" {
+    var allocator = std.testing.allocator;
+    const task = try Task.create(@ptrToInt(test_fn1), true, undefined, allocator, false);
+    defer task.destroy(allocator);
+    try std.testing.expectEqualSlices(usize, task.kernel_stack, &[_]usize{});
+    try std.testing.expectEqual(task.stack_pointer, 0);
+}
+
+test "addVFSHandle" {
+    var task = try Task.create(0, true, undefined, std.testing.allocator, false);
+    defer task.destroy(std.testing.allocator);
+    var node1 = vfs.Node{ .Dir = .{ .fs = undefined, .mount = null } };
+    var node2 = vfs.Node{ .File = .{ .fs = undefined } };
+
+    const handle1 = (try task.addVFSHandle(&node1)) orelse return error.FailedToAddVFSHandle;
+    try expectEqual(handle1, 0);
+    try expectEqual(&node1, task.file_handle_mapping.get(handle1).?);
+    try expectEqual(true, try task.file_handles.isSet(handle1));
+
+    const handle2 = (try task.addVFSHandle(&node2)) orelse return error.FailedToAddVFSHandle;
+    try expectEqual(handle2, 1);
+    try expectEqual(&node2, task.file_handle_mapping.get(handle2).?);
+    try expectEqual(true, try task.file_handles.isSet(handle2));
+}
+
+test "hasFreeVFSHandle" {
+    var task = try Task.create(0, true, undefined, std.testing.allocator, false);
+    defer task.destroy(std.testing.allocator);
+    var node1 = vfs.Node{ .Dir = .{ .fs = undefined, .mount = null } };
+
+    try expect(task.hasFreeVFSHandle());
+
+    _ = (try task.addVFSHandle(&node1)) orelse return error.FailedToAddVFSHandle;
+    try expect(task.hasFreeVFSHandle());
+
+    var i: usize = 0;
+    const free_entries = task.file_handles.num_free_entries;
+    while (i < free_entries) : (i += 1) {
+        try expect(task.hasFreeVFSHandle());
+        _ = task.file_handles.setFirstFree();
+    }
+    try expect(!task.hasFreeVFSHandle());
+}
+
+test "getVFSHandle" {
+    var task = try Task.create(0, true, undefined, std.testing.allocator, false);
+    defer task.destroy(std.testing.allocator);
+    var node1 = vfs.Node{ .Dir = .{ .fs = undefined, .mount = null } };
+    var node2 = vfs.Node{ .File = .{ .fs = undefined } };
+
+    const handle1 = (try task.addVFSHandle(&node1)) orelse return error.FailedToAddVFSHandle;
+    try expectEqual(&node1, (try task.getVFSHandle(handle1)).?);
+
+    const handle2 = (try task.addVFSHandle(&node2)) orelse return error.FailedToAddVFSHandle;
+    try expectEqual(&node2, (try task.getVFSHandle(handle2)).?);
+    try expectEqual(&node1, (try task.getVFSHandle(handle1)).?);
+
+    try expectEqual(task.getVFSHandle(handle2 + 1), null);
+}
+
+test "clearVFSHandle" {
+    var task = try Task.create(0, true, undefined, std.testing.allocator, false);
+    defer task.destroy(std.testing.allocator);
+    var node1 = vfs.Node{ .Dir = .{ .fs = undefined, .mount = null } };
+    var node2 = vfs.Node{ .File = .{ .fs = undefined } };
+
+    const handle1 = (try task.addVFSHandle(&node1)) orelse return error.FailedToAddVFSHandle;
+    const handle2 = (try task.addVFSHandle(&node2)) orelse return error.FailedToAddVFSHandle;
+
+    try task.clearVFSHandle(handle1);
+    try expectEqual(false, try task.hasVFSHandle(handle1));
+
+    try task.clearVFSHandle(handle2);
+    try expectEqual(false, try task.hasVFSHandle(handle2));
+
+    try expectError(Task.Error.VFSHandleNotSet, task.clearVFSHandle(handle2 + 1));
+    try expectError(Task.Error.VFSHandleNotSet, task.clearVFSHandle(handle2));
+    try expectError(Task.Error.VFSHandleNotSet, task.clearVFSHandle(handle1));
+}

test/mock/kernel/arch_mock.zig

@@ -206,11 +206,12 @@ pub fn initMem(payload: BootPayload) Allocator.Error!mem.MemProfile {
     };
 }
 
-pub fn initTask(t: *Task, entry_point: usize, allocator: Allocator) Allocator.Error!void {
+pub fn initTask(t: *Task, entry_point: usize, allocator: Allocator, set_up_stack: bool) Allocator.Error!void {
     // Suppress unused variable warnings
     _ = t;
     _ = entry_point;
     _ = allocator;
+    _ = set_up_stack;
 }
 
 pub fn initKeyboard(allocator: Allocator) Allocator.Error!?*Keyboard {

test/runtime_test.zig

@@ -193,7 +193,7 @@ pub const RuntimeStep = struct {
     ///     Error.TestFailed            - The error if the test failed.
     ///
     fn make(step: *Step) (Thread.SpawnError || ChildProcess.SpawnError || Allocator.Error || Error)!void {
-        const self = @fieldParentPtr(RuntimeStep, "step", step);
+        const self: RuntimeStep = @fieldParentPtr("step", step);
 
         // Create the qemu process
         self.os_proc = try ChildProcess.init(self.argv, self.builder.allocator);
@@ -254,7 +254,7 @@ pub const RuntimeStep = struct {
             };
 
             // put line in the queue
-            var node = self.builder.allocator.create(Node) catch unreachable;
+            const node = self.builder.allocator.create(Node) catch unreachable;
             node.* = .{ .next = null, .data = line };
             self.msg_queue.put(node);
         }