remount a filesystem with libmount from util-linux

remount.c

#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;
}