[CRIU] [PATCH v4 3/3] mount: Restore binfmt_misc content in case of missing mount

[Pavel Emelyanov]

On 07/20/2016 01:13 PM, Kirill Tkhai wrote:
> In case of mount image is not containing binfmt_misc mountpoint,
> scan image directory for binfmt_misc content file (binfmt-misc-xxx).
> If a file is found, add temporary mountpoint to mount tree and
> restore the content in ordinary way. Then, umount temporary mountpoint.
> 
> v4: New
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/mount.c |   61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 59 insertions(+), 2 deletions(-)
> 
> diff --git a/criu/mount.c b/criu/mount.c
> index d583429..8657c36 100644
> --- a/criu/mount.c
> +++ b/criu/mount.c
> @@ -1379,6 +1379,39 @@ static int try_mount_binfmt_misc(struct ns_id *ns, unsigned int *s_dev)
>  	return ret ? -1 : exit_code;
>  }
>  
> +static int find_binfmt_misc_img(unsigned int *s_dev)
> +{
> +	struct dirent *de;
> +	int dfd, ret;
> +	DIR *dir;
> +
> +	*s_dev = 0;
> +	dfd = dup(get_service_fd(IMG_FD_OFF));
> +	dir = fdopendir(dfd);
> +	if (!dir) {
> +		close(dfd);
> +		pr_perror("Can't open img dir\n");
> +		return -1;
> +	}
> +	rewinddir(dir);
> +
> +	errno = 0;
> +	while ((de = readdir(dir)) != NULL) {

Scanning the images dir doesn't look valid. Instead, there should be a proper
collection of this image (like we do with fdinfo-s, sockets and others). Then,
when reading the mountpoint images, the binfmt_misc collected data should be
looked up and orphan data should add the cr-time mountpoints.

> +		if (strncmp(de->d_name, "binfmt-misc-", 12) == 0) {
> +			*s_dev = (unsigned int)strtoul(de->d_name + 12, NULL, 10);
> +			break;
> +		}
> +	}
> +	ret = errno;
> +	if (ret)
> +		pr_perror("Can't read dir\n");
> +	else if (*s_dev)
> +		pr_info("Found binfmt_misc img for dev=%u\n", *s_dev);
> +	closedir(dir);
> +
> +	return ret ? -1 : (*s_dev != 0);
> +}
> +
>  static int binfmt_misc_virtual(struct mount_info *pm)
>  {
>  	return kerndat_fs_virtualized(KERNDAT_FS_STAT_BINFMT_MISC, pm->s_dev);
> @@ -2442,6 +2475,15 @@ static int do_new_mount(struct mount_info *mi)
>  	if (tp->restore && tp->restore(mi))
>  		return -1;
>  
> +	if (!mi->mnt_id) {
> +		/* C-r time mountpoint, umount it */
> +		if (umount(mi->mountpoint) < 0) {

I don't see the corresponding mount() callback. Where is it?

> +			pr_perror("Can't umount %s\n", mi->mountpoint);
> +			return -1;
> +		}
> +		goto out;
> +	}
> +
>  	if (remount_ro && mount(NULL, mi->mountpoint, tp->name,
>  				     MS_REMOUNT | MS_RDONLY, NULL)) {
>  		pr_perror("Unable to apply mount options");
> @@ -2461,7 +2503,7 @@ static int do_new_mount(struct mount_info *mi)
>  	BUG_ON(mi->master_id);
>  	if (restore_shared_options(mi, !mi->shared_id, mi->shared_id, 0))
>  		return -1;
> -
> +out:
>  	mi->mounted = true;
>  
>  	return 0;
> @@ -3324,7 +3366,7 @@ static int populate_roots_yard(void)
>  
>  static int populate_mnt_ns(void)
>  {
> -	struct mount_info *pms;
> +	struct mount_info *pms, *mi;
>  	struct ns_id *nsid;
>  	struct mount_info *roots_mp = NULL;
>  	int ret;
> @@ -3343,6 +3385,21 @@ static int populate_mnt_ns(void)
>  	if (!pms)
>  		return -1;
>  
> +	for (mi = mntinfo; mi != NULL; mi = mi->next) {
> +		if (strcmp(mi->fstype->name, "binfmt_misc") == 0)
> +			break;
> +	}
> +
> +	if (!mi) {
> +		unsigned int s_dev;
> +
> +		ret = find_binfmt_misc_img(&s_dev);
> +		if (ret > 0)
> +			ret = add_cr_time_mount(pms, "binfmt_misc", BINFMT_MISC_HOME, s_dev);
> +		if (ret < 0)
> +			return -1;
> +	}
> +
>  	if (resolve_shared_mounts(mntinfo, pms->master_id))
>  		return -1;
>  
> 
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