From 64dd81fc06afc1d3ecb796f7851e1a54309640be Mon Sep 17 00:00:00 2001
From: Imbus <>
Date: Wed, 10 Sep 2025 08:38:21 +0200
Subject: [PATCH] Mmap_file

---
 mmap_file/.gitignore  |  1 +
 mmap_file/Makefile    | 12 ++++++++++
 mmap_file/mmap_file.c | 56 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 69 insertions(+)
 create mode 100644 mmap_file/.gitignore
 create mode 100644 mmap_file/Makefile
 create mode 100644 mmap_file/mmap_file.c

diff --git a/mmap_file/.gitignore b/mmap_file/.gitignore
new file mode 100644
index 0000000..f0014c4
--- /dev/null
+++ b/mmap_file/.gitignore
@@ -0,0 +1 @@
+mapped.txt
diff --git a/mmap_file/Makefile b/mmap_file/Makefile
new file mode 100644
index 0000000..70f6219
--- /dev/null
+++ b/mmap_file/Makefile
@@ -0,0 +1,12 @@
+CC ?= gcc
+CFLAGS ?= -Wall -O2
+
+TARGET = main.elf
+SRC = mmap_file.c
+
+$(TARGET): $(SRC)
+	@echo CC $@
+	@$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+clean:
+	rm -f $(TARGET)
diff --git a/mmap_file/mmap_file.c b/mmap_file/mmap_file.c
new file mode 100644
index 0000000..781f05f
--- /dev/null
+++ b/mmap_file/mmap_file.c
@@ -0,0 +1,56 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#define FILE_PATH "mapped.txt"
+#define FILE_SIZE 4096
+
+int main() {
+    int fd = open(FILE_PATH, O_RDWR | O_CREAT, 0644);
+    if (fd == -1) {
+        perror("open");
+        return 1;
+    }
+
+    /* We want some space to write */
+    if (ftruncate(fd, FILE_SIZE) == -1) {
+        perror("ftruncate");
+        close(fd);
+        return 1;
+    }
+
+    /* NULL means we do not care where the mapping goes, anywhere in canonical memory will do
+     * PROT_READ/WRITE are just protection flags that allows our process rw rights
+     * MAP_SHARED means our (real time, or close to) changes are visible to other processes mmping the same file */
+    void *file_memory = mmap(NULL, FILE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    if (file_memory == MAP_FAILED) {
+        perror("mmap");
+        close(fd);
+        return 1;
+    }
+
+    const char *message = "This is written to file!";
+    strncpy(file_memory, message, strlen(message) + 1);
+
+    /* Re-truncate the file to known length, otherwise the entire buffer
+     * (4k, with garbage from whatever the kernel gave us) will be in the file*/
+    if (ftruncate(fd, strnlen(message, FILE_SIZE + 1)) == -1) {
+        perror("ftruncate");
+        close(fd);
+        return 1;
+    }
+
+    printf("Mapped region content: %s\n", (char *)file_memory);
+
+    munmap(file_memory, FILE_SIZE);
+
+    close(fd);
+
+    /* Optional finishing step, but i assume you want to inspect the file */
+    // remove(file_path);
+
+    return 0;
+}