Auxiliary mount helper for non-root ZFS mounts

zfs_mount.c

// Compile with:
// cc -DUID=$UID -DUSER=$USER -D_LARGEFILE64_SOURCE -o zfs_mount zfs_mount.c `pkg-config --cflags --libs libzfs`
// then install with:
// sudo cp zfs_mount /usr/local/bin
// sudo setcap cap_sys_admin+ep /usr/local/bin/zfs_mount

#include <libzfs.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

#define STR_AUX(x) #x
#define STR(x) STR_AUX(x)

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

    char* fs_path = argv[1];

    char* user = getlogin();
    uid_t uid = getuid();
    if (strcmp(user, STR(USER)) != 0 || uid != UID) {
        fprintf(stderr, "Bad user: %s (%d)\n", user, uid);
        return 1;
    }

    libzfs_handle_t *g_zfs;
    if ((g_zfs = libzfs_init()) == NULL) {
        fprintf(stderr, "%s\n", libzfs_error_init(errno));
        return 1;
    }

    zfs_handle_t *zhp;
    if ((zhp = zfs_open(g_zfs, fs_path, ZFS_TYPE_FILESYSTEM)) == NULL) {
        fprintf(stderr, "filesystem '%s' cannot be "
            "mounted, does it exist?\n", fs_path);
        libzfs_fini(g_zfs);
        return 1;
    }

    if (zfs_mount(zhp, "", 0)) {
        fprintf(stderr, "zfs_mount() failed: %s\n",
                libzfs_error_description(g_zfs));
        zfs_close(zhp);
        libzfs_fini(g_zfs);
        return 1;
    }

    zfs_close(zhp);
    libzfs_fini(g_zfs);

    return 0;
}