[CRIU] [PATCH 2/3] files-reg: Create ghost files in root directory of a mount

[Pavel Emelyanov]

On 12/15/2015 04:29 PM, Kirill Tkhai wrote:
> Since a deleted file may belong to a deleted directory
> (which, in turn, may belong to another deleted, etc),
> it's necessary to recreate all missing dentries in the path.
> 
> Doing this in mkreg_ghost() is not a good idea, because
> another ghost file may need some of the dentries in the path,
> and this requires to do refcouting of recreated directories.
> 
> To avoid this, we restore a ghost file in the root directory
> of the mount instead.
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  files-reg.c |   37 +++++++++++++++++++++++++++----------
>  1 file changed, 27 insertions(+), 10 deletions(-)
> 
> diff --git a/files-reg.c b/files-reg.c
> index 8469417..e38a2e8 100644
> --- a/files-reg.c
> +++ b/files-reg.c
> @@ -96,11 +96,23 @@ static int note_link_remap(char *path, struct ns_id *nsid)
>  
>  static int mkreg_ghost(char *path, u32 mode, struct ghost_file *gf, struct cr_img *img)
>  {
> -	int gfd, ret;
> +	int gfd, ret, len, i = 0;
> +
> +	len = strlen(path);
> +again:
> +	sprintf(path + len, ".%x", i);
>  
>  	gfd = open(path, O_WRONLY | O_CREAT | O_EXCL, mode);
> -	if (gfd < 0)
> +	if (gfd < 0) {
> +		if (errno != EEXIST)
> +			return -1;
> +		if (++i < INT_MAX)
> +			goto again;
>  		return -1;
> +	}
> +
> +	len = strlen(gf->remap.rpath);
> +	sprintf(gf->remap.rpath + len, ".%x", i);
>  
>  	ret = copy_file(img_raw_fd(img), gfd, 0);
>  	close(gfd);
> @@ -163,6 +175,12 @@ static inline void ghost_path(char *path, int plen,
>  		struct reg_file_info *rfi, RemapFilePathEntry *rfe)
>  {
>  	snprintf(path, plen, "%s.cr.%x.ghost", rfi->path, rfe->remap_id);
> +	/*
> +	 * We create ghost files in root of mount, to avoid (possible)
> +	 * removed intemediate parent directories.
> +	 */
> +	while ((path = strchr(path, '/')) != NULL)
> +		*path = '_';

This hunk doesn't turn path into a file in the 'root of the mount', it turns 
path into a file in the root of the whole tree.

>  }
>  
>  static int open_remap_ghost(struct reg_file_info *rfi,
> @@ -414,17 +432,18 @@ int prepare_remaps(void)
>  	return ret;
>  }
>  
> -static void try_clean_ghost(struct remap_info *ri)
> +static void try_clean_ghost(struct ghost_file *gf)
>  {
>  	char path[PATH_MAX];
>  	int mnt_id, ret;
>  
> -	mnt_id = ri->rfi->rfe->mnt_id; /* rirfirfe %) */
> +	mnt_id = gf->remap.rmnt_id;
>  	ret = rst_get_mnt_root(mnt_id, path, sizeof(path));
>  	if (ret < 0)
>  		return;
>  
> -	ghost_path(path + ret, sizeof(path) - 1, ri->rfi, ri->rfe);
> +	sprintf(path + ret, "/%s", gf->remap.rpath);
> +
>  	if (!unlink(path)) {
>  		pr_info(" `- X [%s] ghost\n", path);
>  		return;
> @@ -437,7 +456,6 @@ static void try_clean_ghost(struct remap_info *ri)
>  	 */
>  
>  	if ((errno == EISDIR)) {
> -		strncpy(path + ret, ri->rfi->path, sizeof(path) - 1);
>  		if (!rmdir(path)) {
>  			pr_info(" `- Xd [%s] ghost\n", path);
>  			return;
> @@ -449,7 +467,7 @@ static void try_clean_ghost(struct remap_info *ri)
>  
>  void try_clean_remaps(int ns_fd)
>  {
> -	struct remap_info *ri;
> +	struct ghost_file *gf;
>  	int old_ns = -1;
>  	int cwd_fd = -1;
>  
> @@ -479,9 +497,8 @@ void try_clean_remaps(int ns_fd)
>  		}
>  	}
>  
> -	list_for_each_entry(ri, &remaps, list)
> -		if (ri->rfe->remap_type == REMAP_TYPE__GHOST)
> -			try_clean_ghost(ri);
> +	list_for_each_entry(gf, &ghost_files, list)
> +		try_clean_ghost(gf);

How do you avoid calling this on link and pid remaps?

>  	if (old_ns >= 0) {
>  		if (setns(old_ns, CLONE_NEWNS) < 0)
> 
> .
>