[CRIU] [PATCH v3 2/4] mount: Add forced mounts sceleton

[Pavel Emelyanov]

On 06/29/2016 02:49 PM, Kirill Tkhai wrote:
> Mechanism for mounts, which are forced by criu during dump stage.
> 
> v2: New patch, splitted from v1's "[2/3] mount: Forced mount unmounted binfmt_misc to do not lost its content"
>     Cleanup for dump failed case is added
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/cr-dump.c       |    1 +
>  criu/include/mount.h |    1 +
>  criu/mount.c         |   76 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 78 insertions(+)
> 
> diff --git a/criu/cr-dump.c b/criu/cr-dump.c
> index 00d28e9..7609544 100644
> --- a/criu/cr-dump.c
> +++ b/criu/cr-dump.c
> @@ -1588,6 +1588,7 @@ static int cr_dump_finish(int ret)
>  	if (ret || post_dump_ret || opts.final_state == TASK_ALIVE) {
>  		network_unlock();
>  		delete_link_remaps();
> +		cleanup_forced_mounts();
>  	}
>  	pstree_switch_state(root_item,
>  			    (ret || post_dump_ret) ?
> diff --git a/criu/include/mount.h b/criu/include/mount.h
> index c7992ac..423b6d0 100644
> --- a/criu/include/mount.h
> +++ b/criu/include/mount.h
> @@ -127,5 +127,6 @@ extern int ext_mount_add(char *key, char *val);
>  extern int mntns_maybe_create_roots(void);
>  extern int read_mnt_ns_img(void);
>  extern void cleanup_mnt_ns(void);
> +extern void cleanup_forced_mounts(void);
>  
>  #endif /* __CR_MOUNT_H__ */
> diff --git a/criu/mount.c b/criu/mount.c
> index 55f248d..4a288e4 100644
> --- a/criu/mount.c
> +++ b/criu/mount.c
> @@ -41,6 +41,15 @@
>  #define LOG_PREFIX "mnt: "
>  
>  static struct fstype fstypes[];
> +static LIST_HEAD(forced_mounts_list);
> +
> +struct forced_mount {
> +	struct list_head list;
> +	unsigned int ns_id;
> +	unsigned int mnt_id;
> +	char *path;
> +	pid_t pid;
> +};

Why separate structure? We have mount_info already, let's add
necessary flags on it.

>  
>  int ext_mount_add(char *key, char *val)
>  {
> @@ -3685,4 +3694,71 @@ int dump_mnt_namespaces(void)
>  	return 0;
>  }
>  
> +static int add_forced_mount(pid_t pid, const char *path)
> +{
> +	struct forced_mount *fm;
> +	int fd, mnt_id, ret = 0;
> +	unsigned int ns_id;
> +
> +	if (read_ns_id(pid, &mnt_ns_desc, &ns_id) < 0 || !ns_id) {

I don't get why we need to read this stuff from kernel, while we have all
the ns_id engine at hands. If you need to add binfmt_misc mountpoint, you
want it per-namespace, not per-task, don't you?

> +		pr_err("Can't read mnt_ns id\n");
> +		return -1;
> +	}
> +
> +	fm = xmalloc(sizeof(*fm));
> +	if (!fm)
> +		return -1;
> +
> +	fd = open(path, O_PATH|O_DIRECTORY);
> +	if (fd < 0) {
> +		pr_perror("Can't open %s\n", path);
> +		goto err_free;
> +	}
> +
> +	ret = get_fd_mntid(fd, &mnt_id);
> +	close(fd);
> +
> +	if (ret < 0) {
> +		pr_err("Can't get mnt_id of %s\n", path);
> +		goto err_free;
> +	}
> +
> +	fm->path = xstrdup(path);
> +	if (!fm->path)
> +		goto err_free;
> +
> +	fm->ns_id = ns_id;
> +	fm->mnt_id = mnt_id;
> +	fm->pid = pid;
> +	list_add(&fm->list, &forced_mounts_list);
> +
> +	return 0;
> +err_free:
> +	pr_err("Can't add forced mount\n");
> +	free(fm);
> +	return -1;
> +}
> +
> +void cleanup_forced_mounts(void)
> +{
> +	struct forced_mount *fm;
> +	int mnt_fd, ret;
> +
> +	list_for_each_entry(fm, &forced_mounts_list, list) {
> +		ret = switch_ns(fm->pid, &mnt_ns_desc, &mnt_fd);
> +		if (ret) {
> +			pr_err("Can't switch to pid's %u mnt_ns\n", fm->pid);
> +			continue;
> +		}
> +
> +		if (umount(fm->path) < 0)
> +			pr_perror("Can't umount forced mount %s\n", fm->path);
> +
> +		if (restore_ns(mnt_fd, &mnt_ns_desc)) {
> +			pr_err("cleanup_forced_mounts exiting with wrong mnt_ns\n");
> +			return;
> +		}
> +	}
> +}
> +
>  struct ns_desc mnt_ns_desc = NS_DESC_ENTRY(CLONE_NEWNS, "mnt");
> 
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