[CRIU] [PATCH] mount: Create target of bind mount if it doesn't exist

[Pavel Emelyanov]

On 08/28/2014 07:43 PM, Saied Kazemi wrote:
> I have seen a similar case where /dev/null is missing (Docker using UnionFS).  While this patch fixes
> the issue, I am wondering why the target file should be missing to start with and whether *always*
> recreating missing target files could be masking more serious issues.  Any thoughts?

+1  I'd also like to know the reasons why the mountpoint target doesn't exist.
AFAIK rmdir/unlink doesn't work on dirs/files that are mountpoints.

> --Saied
> 
> 
> 
> On Thu, Aug 28, 2014 at 8:27 AM, Tycho Andersen <tycho.andersen at canonical.com <mailto:tycho.andersen at canonical.com>> wrote:
> 
>     If the target of a bind mount doesn't exist, create it. In particular, this
>     happens with /dev/ptmx across hosts under LXC. We could also mkdir -p any path
>     to the target, although I'm not sure if that is a case that occurrs in the
>     wild.
> 
>     Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com <mailto:tycho.andersen at canonical.com>>
>     ---
>      mount.c | 18 ++++++++++++++++++
>      1 file changed, 18 insertions(+)
> 
>     diff --git a/mount.c b/mount.c
>     index 9bb8a17..2108907 100644
>     --- a/mount.c
>     +++ b/mount.c
>     @@ -1346,6 +1346,24 @@ static int do_bind_mount(struct mount_info *mi)
>                     root = rpath;
>      do_bind:
>                     pr_info("\tBind %s to %s\n", root, mi->mountpoint);
>     +
>     +               if (access(mi->mountpoint, F_OK)) {
>     +                       if (errno == ENOENT) {
>     +                               FILE *f;
>     +
>     +                               f = fopen(mi->mountpoint, "w");
>     +                               if (!f) {
>     +                                       pr_perror("couldn't write 0 length %s", mi->mountpoint);
>     +                                       return -1;
>     +                               }
>     +
>     +                               fclose(f);
>     +                       } else {
>     +                               pr_perror("Couldn't access %s", mi->mountpoint);
>     +                               return -1;
>     +                       }
>     +               }
>     +
>                     if (mount(root, mi->mountpoint, NULL,
>                                             MS_BIND, NULL) < 0) {
>                             pr_perror("Can't mount at %s", mi->mountpoint);
>     --
>     1.9.1
> 
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> 
> 
> 
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