[CRIU] [PATCH 2/4] mount: add support for external block devices

[Andrew Vagin]

On Tue, Apr 19, 2016 at 07:59:07AM -0700, Andrew Vagin wrote:
> On Tue, Apr 19, 2016 at 01:19:48PM +0300, Pavel Emelyanov wrote:
> > On 04/19/2016 03:44 AM, Andrew Vagin wrote:
> > > On Mon, Apr 18, 2016 at 07:36:52PM +0300, Pavel Emelyanov wrote:
> > >> On 04/15/2016 01:19 AM, Andrey Vagin wrote:
> > >>> From: Andrew Vagin <avagin at virtuozzo.com>
> > >>>
> > >>> It works like enable-fs, in this case we allow to mount a specified block device.
> > >>>
> > >>> Options:
> > >>> dump:		--external mnt[MAJOR:MINOR]
> > >>> restore:	--mnt-ext-map mnt[MAJOR:MINOR]:DEVPATH
> > >>
> > >> We don't have --mnt-ext-map option :\
> > > 
> > > I mean --ext-mount-map
> > >>
> > >> Please, explain what the option arguments mean.
> > 
> > Please, explain what the option arguments mean.
> 
> We save major and minor numbers for each mount, then on restore
> we can say that DEVPATH should be mounted instead of the origin device.
> 
> For external devices, we call mount() with options, file system and
> flags which have been parsed from mountinfo during dump. The behaviour
> is the same with enabled file systems, but we can change the source
> argument.
> 
> int mount(const char *source, const char *target,
>                  const char *filesystemtype, unsigned long mountflags,
>                  const void *data);

I do this to support a second ploop device in OpenVZ container. ploop is
a block device dlike linux loop device with a few additional features.

Each time when a new ploop is created, it gets an random name, so we
have to be able to restore a container with another ploop name.

--ext-mount-map allows to specify which device should be mounted instead
of a previos one.

> 
> 
> > 
> > >>> https://jira.sw.ru/browse/PSBM-39381
> > >>>
> > >>> Signed-off-by: Andrew Vagin <avagin at virtuozzo.com>
> > >>> ---
> > >>>  criu/crtools.c    |  1 +
> > >>>  criu/mount.c      | 11 +++++++++++
> > >>>  criu/proc_parse.c | 10 ++++++++++
> > >>>  3 files changed, 22 insertions(+)
> > >>>
> > >>> diff --git a/criu/crtools.c b/criu/crtools.c
> > >>> index 02a24e7..3598b1b 100644
> > >>> --- a/criu/crtools.c
> > >>> +++ b/criu/crtools.c
> > >>> @@ -882,6 +882,7 @@ usage:
> > >>>  "                        Formats of RES:\n"
> > >>>  "                            tty[rdev:dev]\n"
> > >>>  "                            file[mnt_id:inode]\n"
> > >>> +"                            mnt[MAJOR/MINOR]\n"
> > >>>  "  --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/mount.c b/criu/mount.c
> > >>> index f57b10c..85eeeda 100644
> > >>> --- a/criu/mount.c
> > >>> +++ b/criu/mount.c
> > >>> @@ -1818,6 +1818,8 @@ static struct fstype *__find_fstype_by_name(char *fst, bool force_auto)
> > >>>  {
> > >>>  	int i;
> > >>>  
> > >>> +	if (fst == (void *) FSTYPE__AUTO)
> > >>> +		return &fstypes[1];
> > >>>  	/*
> > >>>  	 * This fn is required for two things.
> > >>>  	 * 1st -- to check supported filesystems (as just mounting
> > >>> @@ -2091,6 +2093,15 @@ static char *resolve_source(struct mount_info *mi)
> > >>>  
> > >>>  	if (mi->fstype->code == FSTYPE__AUTO) {
> > >>>  		struct stat st;
> > >>> +		char devstr[64];
> > >>> +		struct ext_mount *key;
> > >>> +
> > >>> +		snprintf(devstr, sizeof(devstr), "mnt[%d/%d]",
> > >>> +				kdev_major(mi->s_dev), kdev_minor(mi->s_dev));
> > >>> +
> > >>> +		key = ext_mount_lookup(devstr);
> > >>> +		if (key)
> > >>> +			return key->val;
> > >>>  
> > >>>  		if (!stat(mi->source, &st) && S_ISBLK(st.st_mode) &&
> > >>>  		    major(st.st_rdev) == kdev_major(mi->s_dev) &&
> > >>> diff --git a/criu/proc_parse.c b/criu/proc_parse.c
> > >>> index 2dd8dc4..55f0f5e 100644
> > >>> --- a/criu/proc_parse.c
> > >>> +++ b/criu/proc_parse.c
> > >>> @@ -1292,6 +1292,16 @@ static int parse_mountinfo_ent(char *str, struct mount_info *new, char **fsname)
> > >>>  
> > >>>  	new->fstype = find_fstype_by_name(*fsname);
> > >>>  
> > >>> +	if (new->fstype->code == FSTYPE__UNSUPPORTED) {
> > >>> +		char devstr[64];
> > >>> +
> > >>> +		snprintf(devstr, sizeof(devstr), "mnt[%d/%d]",
> > >>> +				kdev_major(new->s_dev),  kdev_minor(new->s_dev));
> > >>> +
> > >>> +		if (external_lookup_id(devstr))
> > >>> +			new->fstype = find_fstype_by_name((void *)FSTYPE__AUTO);
> > >>> +	}
> > >>> +
> > >>>  	new->options = xmalloc(strlen(opt) + 1);
> > >>>  	if (!new->options)
> > >>>  		goto err;
> > >>>
> > >>
> > > .
> > > 
> >