[CRIU] [PATCH 3/4] [v4] mount: add support for external block devices

[Pavel Emelyanov]

On 04/28/2016 07:53 PM, 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:      --external dev[MAJOR:MINOR]:VAL
> restore:   --external 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
> v4: use --external on dump and on restore
> 
> Signed-off-by: Andrew Vagin <avagin at virtuozzo.com>
> ---
>  criu/crtools.c       | 10 ++++------
>  criu/files.c         | 14 ++++++++++++++
>  criu/include/files.h |  1 +
>  criu/mount.c         | 37 +++++++++++++++++++++++++++++++------
>  4 files changed, 50 insertions(+), 12 deletions(-)
> 
> diff --git a/criu/crtools.c b/criu/crtools.c
> index 7a0f977..774173d 100644
> --- a/criu/crtools.c
> +++ b/criu/crtools.c
> @@ -698,11 +698,6 @@ int main(int argc, char *argv[], char *envp[])
>  	if (log_init(opts.output))
>  		return 1;
>  
> -	if (!list_empty(&opts.external) && strcmp(argv[optind], "dump")) {
> -		pr_err("--external is dump-only option\n");
> -		return 1;
> -	}
> -
>  	if (!list_empty(&opts.inherit_fds)) {
>  		if (strcmp(argv[optind], "restore")) {
>  			pr_err("--inherit-fd is restore-only option\n");
> @@ -878,9 +873,12 @@ usage:
>  "                        force criu to (try to) dump/restore these filesystem's\n"
>  "                        mountpoints even if fs is not supported.\n"
>  "  --external RES        dump objects from this list as external resources:\n"
> -"                        Formats of RES:\n"
> +"                        Formats of RES on dump:\n"
>  "                            tty[rdev:dev]\n"
>  "                            file[mnt_id:inode]\n"
> +"                            dev[maj:min]:VAL\n"
> +"                        Formats of RES on restore:\n"
> +"                            VAL:DEVPATH\n"

DEVPATH? This looks like --external for restore is device-only feature, while
it should not be such.

>  "  --inherit-fd fd[<num>]:<existing>\n"
>  "                        Inherit file descriptors. This allows to treat file descriptor\n"
>  "                        <num> as being already opened via <existing> one and instead of\n"
> diff --git a/criu/files.c b/criu/files.c
> index d3ce116..dfa3603 100644
> --- a/criu/files.c
> +++ b/criu/files.c
> @@ -1627,3 +1627,17 @@ bool external_lookup_id(char *id)
>  			return true;
>  	return false;
>  }
> +
> +char *external_lookup_by_key(char *key)

criu/files.c will win from using this function.

> +{
> +	struct external *ext;
> +	int len = strlen(key);
> +
> +	list_for_each_entry(ext, &opts.external, node) {
> +		if (strncmp(ext->id, key, len))
> +			continue;
> +		if (ext->id[len] == ':')
> +			return ext->id + len + 1;
> +	}
> +	return NULL;
> +}
> diff --git a/criu/include/files.h b/criu/include/files.h
> index 363437b..1894f09 100644
> --- a/criu/include/files.h
> +++ b/criu/include/files.h
> @@ -210,6 +210,7 @@ extern int inherit_fd_fini(void);
>  
>  extern bool external_lookup_id(char *id);
>  extern int inherit_fd_lookup_id(char *id);
> +extern char *external_lookup_by_key(char *id);
>  
>  extern bool inherited_fd(struct file_desc *, int *fdp);
>  
> diff --git a/criu/mount.c b/criu/mount.c
> index 78fe3a3..cad89ae 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 +489,33 @@ 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) {

Shouldn't this be FSTYE__AUTO instead?

> +		char *val;
> +

A code comment here and ...

> +		val = external_lookup_by_key(devstr);
> +		if (val) {

... a pr_info("Whee! $some_explanation_of_whee") here will make the patch perfect.

> +			info->fstype = &fstypes[1];
> +			BUG_ON(info->fstype->code != FSTYPE__AUTO);
> +			xfree(info->source);
> +			info->source = xstrdup(val);
> +			return 0;
> +		}
> +	}
> +
> +	return -ENOTSUP;
>  }
>  
>  static struct mount_info *find_widest_shared(struct mount_info *m)
> @@ -2086,6 +2106,11 @@ static char *resolve_source(struct mount_info *mi)
>  
>  	if (mi->fstype->code == FSTYPE__AUTO) {
>  		struct stat st;
> +		char *val;
> +
> +		val = external_lookup_by_key(mi->source);
> +		if (val)
> +			return val;
>  
>  		if (!stat(mi->source, &st) && S_ISBLK(st.st_mode) &&
>  		    major(st.st_rdev) == kdev_major(mi->s_dev) &&
>