Re: [PATCH] man/man2/move_mount.2: document EINVAL on multiple instances

[Askar Safin <safinaskar@gmail.com>]

Luca Boccassi <luca.boccassi@gmail.com>:
> IIRC Christian said this was working as intended? Just fsmount() to
> create a detached mount, and then try to apply it multiple times with
> multiple move_mount(), and the second and subsequent ones will fail
> with EINVAL

I just tested current mainline kernel (67029a49db6c).
And move_mount doesn't return EINVAL in this case (move_mount succeds).
This means that either EINVAL is not intended, either current mainline kernel
is buggy.

I tested this in Qemu in very minimal environment (rdinit=/bin/busybox sh).

See C source below.

-- 
Askar Safin

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/mount.h>

#define ASSERT(cond) if (!(cond)) { \
    fprintf (stderr, "%s: assertion failed\n", #cond); \
    exit (1); \
}

#define ASSERT_ERRNO(cond) if (!(cond)) { \
    fprintf (stderr, "%d: ", __LINE__); \
    perror (#cond); \
    exit (1); \
}

int
main (void)
{
    ASSERT_ERRNO (mkdir ("/a", 0777) == 0);
    ASSERT_ERRNO (mkdir ("/b", 0777) == 0);
    ASSERT_ERRNO (mkdir ("/c", 0777) == 0);
    {
        {
            int fsfd = fsopen ("tmpfs", 0);
            ASSERT_ERRNO (fsfd != -1);
            ASSERT_ERRNO (fsconfig (fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) == 0);
            {
                int mntfd = fsmount (fsfd, 0, 0);
                ASSERT_ERRNO (mntfd != -1);
                ASSERT_ERRNO (move_mount (mntfd, "", AT_FDCWD, "/a", MOVE_MOUNT_F_EMPTY_PATH) == 0);
                ASSERT_ERRNO (move_mount (mntfd, "", AT_FDCWD, "/b", MOVE_MOUNT_F_EMPTY_PATH) == 0);
                ASSERT_ERRNO (move_mount (mntfd, "", AT_FDCWD, "/c", MOVE_MOUNT_F_EMPTY_PATH) == 0);
                ASSERT_ERRNO (close (mntfd) == 0);
            }
            ASSERT_ERRNO (close (fsfd) == 0);
        }
        ASSERT_ERRNO (umount ("/c") == 0);
    }
}