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

[Pavel Emelyanov]

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?

> +		!strcmp(c->source, mi->source) &&
> +		!strcmp(c->options, mi->options) &&
> +		c->fstype == mi->fstype);
> +}
> +
>  static struct mount_info *mnt_build_ids_tree(struct mount_info *list)
>  {
>  	struct mount_info *m, *root = NULL;
> @@ -178,6 +188,21 @@ static void mnt_tree_show(struct mount_info *tree, int off)
>  	pr_info("%*s<--\n", off, "");
>  }
>  
> +static inline int is_root(char *p)
> +{
> +	return p[0] == '/' && p[1] == '\0';
> +}
> +
> +static inline int is_root_mount(struct mount_info *mi)
> +{
> +	return is_root(mi->mountpoint);
> +}
> +
> +static inline int fsroot_mounted(struct mount_info *mi)
> +{
> +	return is_root(mi->root);
> +}

Why do you move this code in this patch?

> +
>  static int collect_shared(struct mount_info *info)
>  {
>  	struct mount_info *m, *t;
> @@ -197,6 +222,7 @@ static int collect_shared(struct mount_info *info)
>  		for (t = info; t && (share || master); t = t->next) {
>  			if (t == m)
>  				continue;
> +

Trash.

>  			if (master && t->shared_id == m->master_id) {
>  				pr_debug("The mount %d is slave for %d\n", m->mnt_id, t->mnt_id);
>  				list_add(&m->mnt_slave, &t->mnt_slave_list);
> @@ -211,13 +237,20 @@ static int collect_shared(struct mount_info *info)
>  				list_add(&m->mnt_share, &t->mnt_share);
>  			}
>  		}
> -		if (!master)
> -			continue;
>  
> -		pr_err("Mount %d (master_id: %d shared_id: %d) "
> -		       "has unreachable sharing\n", m->mnt_id,
> -			m->master_id, m->shared_id);
> -		return -1;
> +		if (master) {
> +			pr_err("Mount %d (master_id: %d shared_id: %d) "
> +			       "has unreachable sharing\n", m->mnt_id,
> +				m->master_id, m->shared_id);
> +			return -1;
> +		}
> +
> +		/* 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.

> +			}
>  	}
>  
>  	return 0;
> @@ -432,16 +465,6 @@ static struct fstype *decode_fstype(u32 fst)
>  	return &fstypes[fst];
>  }
>  
> -static inline int is_root(char *p)
> -{
> -	return p[0] == '/' && p[1] == '\0';
> -}
> -
> -static inline int is_root_mount(struct mount_info *mi)
> -{
> -	return is_root(mi->mountpoint);
> -}
> -
>  static int dump_one_mountpoint(struct mount_info *pm, int fd)
>  {
>  	MntEntry me = MNT_ENTRY__INIT;
> @@ -565,6 +588,7 @@ static int do_new_mount(struct mount_info *mi)
>  {
>  	char *src;
>  	struct fstype *tp = mi->fstype;
> +	struct mount_info *t;
>  
>  	src = resolve_source(mi);
>  	if (!src)
> @@ -579,18 +603,24 @@ static int do_new_mount(struct mount_info *mi)
>  	if (tp->restore && tp->restore(mi))
>  		return -1;
>  
> +	list_for_each_entry(t, &mi->mnt_bind, mnt_bind)
> +		t->bind = mi;
> +
>  	return 0;
>  }
>  
>  static int do_bind_mount(struct mount_info *mi)
>  {
> -	pr_err("No bind mounts at %s\n", mi->mountpoint);
> -	return -1;
> -}
> +	char rpath[PATH_MAX];
>  
> -static inline int fsroot_mounted(struct mount_info *mi)
> -{
> -	return is_root(mi->root);
> +	snprintf(rpath, sizeof(rpath), "%s%s", mi->bind->mountpoint, mi->root);
> +
> +	if (mount(rpath, mi->mountpoint, NULL,
> +				MS_BIND, NULL) < 0) {
> +		pr_perror("Can't mount at %s", mi->mountpoint);
> +		return -1;
> +	}
> +	return 0;
>  }
>  
>  static int do_mount_one(struct mount_info *mi)
> @@ -704,6 +734,7 @@ struct mount_info *mnt_entry_alloc()
>  		INIT_LIST_HEAD(&new->siblings);
>  		INIT_LIST_HEAD(&new->mnt_slave_list);
>  		INIT_LIST_HEAD(&new->mnt_share);
> +		INIT_LIST_HEAD(&new->mnt_bind);
>  		new->mnt_master = NULL;
>  	}
>  	return new;
>