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gdamjan/remount.c

Created December 29, 2024 17:32
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  1. gdamjan created this gist Dec 29, 2024.
    80 changes: 80 additions & 0 deletions remount.c
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,80 @@
    #define _GNU_SOURCE
    #include <libmount/libmount.h>
    #include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    #include <errno.h>

    /*
    * gcc -o remount-rw remount.c `pkgconf --libs mount`
    */

    int remount_rw(const char *target) {
    struct libmnt_context *cxt;
    struct libmnt_table *tb = NULL;
    struct libmnt_fs *fs;
    const char *options;
    char *new_opts = NULL;
    int rc = -1;

    // Create new mounting context
    cxt = mnt_new_context();
    if (!cxt) {
    fprintf(stderr, "Failed to initialize libmount context\n");
    return -1;
    }

    // Read current mount table
    if (mnt_context_get_mtab(cxt, &tb)) {
    fprintf(stderr, "Failed to read mtab\n");
    goto cleanup;
    }

    // Find the filesystem entry for our target
    fs = mnt_table_find_target(tb, target, MNT_ITER_BACKWARD);
    if (!fs) {
    fprintf(stderr, "Mount point %s not found\n", target);
    goto cleanup;
    }

    // Get current mount options
    options = mnt_fs_get_options(fs);
    if (!options) {
    fprintf(stderr, "Failed to get current mount options\n");
    goto cleanup;
    }

    // Create new options string with "remount,rw"
    if (asprintf(&new_opts, "%s%sremount,rw",
    options,
    strlen(options) > 0 ? "," : "") == -1) {
    fprintf(stderr, "Failed to create new options string\n");
    goto cleanup;
    }

    // Set up remount operation
    mnt_context_set_target(cxt, target);
    mnt_context_set_options(cxt, new_opts);
    mnt_context_set_mflags(cxt, MS_REMOUNT);

    // Perform the remount
    rc = mnt_context_mount(cxt);
    if (rc) {
    fprintf(stderr, "Remount failed: %s\n", strerror(errno));
    rc = -1;
    }

    cleanup:
    free(new_opts);
    mnt_free_context(cxt);
    return rc;
    }

    int main(int argc, char *argv[]) {
    if (argc != 2) {
    fprintf(stderr, "Usage: %s <mount_point>\n", argv[0]);
    return 1;
    }

    return remount_rw(argv[1]) == 0 ? 0 : 1;
    }