[CRIU] [PATCH 5/9] mounts: handle bind-mounts

[Andrew Vagin]

On Wed, Jul 10, 2013 at 02:52:48PM +0400, Pavel Emelyanov wrote:
> On 07/10/2013 12:40 PM, Andrew Vagin wrote:
> > On Tue, Jul 09, 2013 at 08:41:34PM +0400, Pavel Emelyanov wrote:
> >> On 07/09/2013 03:05 PM, Andrey Vagin wrote:
> >>> A non-root mount is bind-mounted to a proper root mount.
> >>>
> >>> Non-root mount without root mount is not supported yet
> >>>
> >>> Signed-off-by: Andrey Vagin <avagin at openvz.org>
> >>> ---
> >>>  include/proc_parse.h |  2 ++
> >>>  mount.c              | 75 +++++++++++++++++++++++++++++++++++++---------------
> >>>  2 files changed, 55 insertions(+), 22 deletions(-)
> >>>
> >>> diff --git a/include/proc_parse.h b/include/proc_parse.h
> >>> index 99255c4..1325424 100644
> >>> --- a/include/proc_parse.h
> >>> +++ b/include/proc_parse.h
> >>> @@ -114,9 +114,11 @@ struct mount_info {
> >>>  
> >>>  	/* tree linkage */
> >>>  	struct mount_info *parent;
> >>> +	struct mount_info *bind;
> >>>  	struct list_head children;
> >>>  	struct list_head siblings;
> >>>  
> >>> +	struct list_head mnt_bind;
> >>
> >> Document the fields please.
> >>
> >>>  	struct list_head mnt_share;	/* circular list of shared mounts */
> >>>  	struct list_head mnt_slave_list;/* list of slave mounts */
> >>>  	struct list_head mnt_slave;	/* slave list entry */
> >>> diff --git a/mount.c b/mount.c
> >>> index 640cd12..31b1f3c 100644
> >>> --- a/mount.c
> >>> +++ b/mount.c
> >>> @@ -77,6 +77,16 @@ struct mount_info *lookup_mnt_sdev(unsigned int s_dev)
> >>>  	return NULL;
> >>>  }
> >>>  
> >>> +/* two bind-mounts are reported as equal if bind is true */
> >>> +static bool mntcmp(struct mount_info* mi, struct mount_info *c, bool bind)
> >>> +{
> >>> +	return (mi->s_dev == c->s_dev &&
> >>> +		(bind || !strcmp(c->root, mi->root)) &&
> >>
> >> I see no callers of these with bind == true. Where is it?
> > 
> > in the next patches
> > 
> >>
> >>> +		!strcmp(c->source, mi->source) &&
> >>> +		!strcmp(c->options, mi->options) &&
> > 
> > ...
> >>> +
> >>> +		/* Search bind-mounts */
> >>> +		if (list_empty(&m->mnt_bind))
> >>> +			for (t = m->next; t; t = t->next) {
> >>> +				if (mntcmp(m, t, true))
> >>> +					list_add(&t->mnt_bind, &m->mnt_bind);
> >>
> >> I don't understand what the mnt_bind list links together.
> > 
> > It links together all mounts, which are the same except root. Only one
> 
> What does "mounts are the same" mean?

Two mounts are the same, if their sources, fstypes, options are equals.

mount -t ext4 -o ro /dev/sda1 /xxx
mount -t ext4 -o ro /dev/sda1 /yyy

this is equal to
mount -t ext4 -o ro /dev/sda1 /xxx
mount --bind /yyy /xxx

isn't it?

> 
> > of them must be mounted and all other can be bind-mounted
> > 
> >>
> >>> +			}
> >>>  	}
> >>>  
> >>>  	return 0;
> >>> @@ -432,16 +465,6 @@ static struct fstype *decode_fstype(u32 fst)
> >>>  	return &fstypes[fst];
> >>>  }
> >>>  
> > .
> > 
> 
>