[CRIU] [PATCH 3/4] mount: add support for external block devices (v3)

[Pavel Emelyanov]

On 04/22/2016 09:12 AM, Andrey Vagin wrote:
> From: Andrew Vagin <avagin at virtuozzo.com>
> 
> The idea is to allow to dump and restore mounts of
> a specified block device.
> 
> Options:
> dump:		--ext-mount-map dev[MAJOR:MINOR]:VAL

Why dev[MAJOR:MINOR]? Isn't just path (which is a mountpoint) enough?

> restore:	--ext-mount-map VAL:DEVPATH
> 
> If we find a mount with a specified block device, we
> set its type into FSTYPE__AUTO and write VAL into
> the "source" field.
> 
> VAL is replaced on DEVPATH on restore.
> 
> https://jira.sw.ru/browse/PSBM-39381
> 
> v2: use --ext-mount-map instead of --external on dump
> v3: clean up
> 
> Signed-off-by: Andrew Vagin <avagin at virtuozzo.com>
> ---
>  Documentation/criu.txt |  6 +++---
>  criu/mount.c           | 35 +++++++++++++++++++++++++++++------
>  2 files changed, 32 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/criu.txt b/Documentation/criu.txt
> index 1982f5d..07da757 100644
> --- a/Documentation/criu.txt
> +++ b/Documentation/criu.txt
> @@ -176,9 +176,9 @@ In other words, do not use it until really needed.
>      where locks are not holed by someone outside of it.
>  
>  *-M*, *--ext-mount-map* '<KEY>'*:*'<VAL>'::
> -    Setup mapping for external mounts. '<KEY>' is a mountpoint inside container
> -    and corresponding '<VAL>' is a string that will be written into the image
> -    as mountpoint\'s root value.
> +    Setup mapping for external mounts. '<KEY>' is a mountpoint or a device
> +    (dev[maj:min]]) inside container and corresponding '<VAL>' is a string
> +    that will be written into the image as mountpoint\'s root or source value.
>  
>  *--link-remap*::
>      Allow one to link unlinked files back when possible (modifies FS till *restore*).
> diff --git a/criu/mount.c b/criu/mount.c
> index f57b10c..f8d0cc2 100644
> --- a/criu/mount.c
> +++ b/criu/mount.c
> @@ -40,6 +40,8 @@
>  #undef	LOG_PREFIX
>  #define LOG_PREFIX "mnt: "
>  
> +static struct fstype fstypes[];
> +
>  int ext_mount_add(char *key, char *val)
>  {
>  	struct ext_mount *em;
> @@ -487,15 +489,31 @@ static void mnt_tree_show(struct mount_info *tree, int off)
>  static int try_resolve_ext_mount(struct mount_info *info)
>  {
>  	struct ext_mount *em;
> +	char devstr[64];
>  
>  	em = ext_mount_lookup(info->mountpoint + 1 /* trim the . */);
> -	if (em == NULL)
> -		return -ENOTSUP;
> +	if (em) {
> +		pr_info("Found %s mapping for %s mountpoint\n",
> +				em->val, info->mountpoint);
> +		info->external = em;
> +		return 0;
> +	}
>  
> -	pr_info("Found %s mapping for %s mountpoint\n",
> -			em->val, info->mountpoint);
> -	info->external = em;
> -	return 0;
> +	snprintf(devstr, sizeof(devstr), "dev[%d/%d]",
> +			kdev_major(info->s_dev),  kdev_minor(info->s_dev));
> +
> +	if (info->fstype->code == FSTYPE__UNSUPPORTED) {
> +		em = ext_mount_lookup(devstr);
> +		if (em) {
> +			info->fstype = &fstypes[1];
> +			BUG_ON(info->fstype->code != FSTYPE__AUTO);
> +			xfree(info->source);
> +			info->source = xstrdup(em->val);
> +			return 0;
> +		}
> +	}
> +
> +	return -ENOTSUP;
>  }
>  
>  static struct mount_info *find_widest_shared(struct mount_info *m)
> @@ -2091,6 +2109,11 @@ static char *resolve_source(struct mount_info *mi)
>  
>  	if (mi->fstype->code == FSTYPE__AUTO) {
>  		struct stat st;
> +		struct ext_mount *key;
> +
> +		key = ext_mount_lookup(mi->source);
> +		if (key)
> +			return key->val;
>  
>  		if (!stat(mi->source, &st) && S_ISBLK(st.st_mode) &&
>  		    major(st.st_rdev) == kdev_major(mi->s_dev) &&
>