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

[Andrew Vagin]

On Fri, May 06, 2016 at 03:17:00PM +0300, Pavel Emelyanov wrote:
> 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.

Currently VAL is used only with the dev[maj:min] key, so here is only
DEVPATH now. In a future we can add new key:value pairs.

> 
> >  "  --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?

No. It's FSTYPE__UNSUPPORTED at this moment.
> 
> > +		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) &&
> > 
>