[CRIU] [PATCH 1/3] mount: cut a common part of sources for bind-mounts

[Andrew Vagin]

On Thu, Apr 10, 2014 at 03:05:28PM +0400, Pavel Emelyanov wrote:
> On 04/10/2014 02:52 PM, Andrey Vagin wrote:
> 
> A couple of examples and "What for?" answer would form nice comment.

The source of the root mount may be not equal to "/" and we need to take
this fact into account, when we bind-mount it to somewhere.

For example:

11877 ?        Ss     0:00 ./bind-mount --pidfile=bind-mount.pid --outfile=bind-mount.out --dirname=bind-mount.test
11880 ?        Ss     0:00  \_ ./bind-mount --pidfile=bind-mount.pid --outfile=bind-mount.out --dirname=bind-mount.test
[root at avagin-fc19-cr crtools]# cat /proc/11880/mountinfo
68 42 8:3 /root/git/crtools/test / rw,relatime - ext4 /dev/sda3 rw,data=ordered
43 68 0:33 / /proc rw,relatime - proc proc rw
44 68 0:34 / /dev/pts rw,relatime - devpts pts rw,mode=666,ptmxmode=666
45 68 8:3 /root/git/crtools/test/zdtm/live/static/bind-mount.test/test /zdtm/live/static/bind-mount.test/bind rw,relatime - ext4 /dev/sda3 rw,data=ordered

The 45 mount is bind-mount of the 68 mount.
mi(45)->root = /root/git/crtools/test/zdtm/live/static/bind-mount.test/test
mi(68)->root = /root/git/crtools/test

so the comman part is "/root/git/crtools/test" and the command is
mount --bind /zdtm/live/static/bind-mount.test/test /zdtm/live/static/bind-mount.test/bind

> 
> > Signed-off-by: Andrey Vagin <avagin at openvz.org>
> > ---
> >  mount.c | 15 +++++++++++++--
> >  1 file changed, 13 insertions(+), 2 deletions(-)
> > 
> > diff --git a/mount.c b/mount.c
> > index 3a37033..c7fba51 100644
> > --- a/mount.c
> > +++ b/mount.c
> > @@ -1137,11 +1137,22 @@ static int restore_ext_mount(struct mount_info *mi)
> >  
> >  static int do_bind_mount(struct mount_info *mi)
> >  {
> > -	char rpath[PATH_MAX];
> >  	bool shared = mi->shared_id && mi->shared_id == mi->bind->shared_id;
> >  
> >  	if (!mi->need_plugin) {
> > -		snprintf(rpath, sizeof(rpath), "%s%s", mi->bind->mountpoint, mi->root);
> > +		char rpath[PATH_MAX];
> > +		int tok = 0;
> > +
> > +		/* Cut common part of root */
> > +		while (mi->root[tok] == mi->bind->root[tok]) {
> > +			tok++;
> > +			if (mi->bind->root[tok] == '\0')
> > +				break;
> > +			BUG_ON(mi->root[tok] == '\0');
> > +		}
> > +
> > +		snprintf(rpath, sizeof(rpath), "%s/%s",
> > +				mi->bind->mountpoint, mi->root + tok);
> >  		pr_info("\tBind %s to %s\n", rpath, mi->mountpoint);
> >  
> >  		if (mount(rpath, mi->mountpoint, NULL,
> > 
> 
>