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

[Andrew Vagin]

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);


> 
> >>> 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;
> >>>
> >>
> > .
> > 
>