[CRIU] [PATCH 2/3] file: add a general approach for external files

[Pavel Emelyanov]

On 01/21/2016 05:07 AM, Andrey Vagin wrote:
> From: Andrew Vagin <avagin at virtuozzo.com>
> 
> The idea is to call open_cb for /proc/self/fd/X,
> where X is an externa file descriptor.
> 
> This approach works for files and fifo.

Plz, describe how this is supposed to be used and how this correlates
with the --inherit-fd one.

> Signed-off-by: Andrew Vagin <avagin at virtuozzo.com>
> ---
>  crtools.c   |  2 ++
>  files-reg.c | 29 +++++++++++++++++++++++++----
>  2 files changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/crtools.c b/crtools.c
> index 039b7a0..fa27622 100644
> --- a/crtools.c
> +++ b/crtools.c
> @@ -781,6 +781,7 @@ usage:
>  "  --external RES        dump objects from this list as external resources:\n"
>  "                        Formats of RES:\n"
>  "                            tty[rdev:dev]\n"
> +"                            files[mnt_id:inode]\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"
> @@ -788,6 +789,7 @@ usage:
>  "                            tty[rdev:dev]\n"
>  "                            pipe[inode]\n"
>  "                            socket[inode]\n"
> +"                            files[mnt_id:inode]\n"
>  "\n"
>  "* Logging:\n"
>  "  -o|--log-file FILE    log file name\n"
> diff --git a/files-reg.c b/files-reg.c
> index ea66af0..ec74272 100644
> --- a/files-reg.c
> +++ b/files-reg.c
> @@ -1021,6 +1021,7 @@ int dump_one_reg_file(int lfd, u32 id, const struct fd_parms *p)
>  	struct fd_link _link, *link;
>  	struct ns_id *nsid;
>  	struct cr_img *rimg;
> +	char ext_id[64];
>  
>  	RegFileEntry rfe = REG_FILE_ENTRY__INIT;
>  
> @@ -1031,6 +1032,14 @@ int dump_one_reg_file(int lfd, u32 id, const struct fd_parms *p)
>  	} else
>  		link = p->link;
>  
> +
> +	snprintf(ext_id, sizeof(ext_id), "@file[%x:%"PRIx64"]", p->mnt_id, p->stat.st_ino);
> +	if (external_lookup_id(ext_id + 1)) {
> +		/* the first symbol will be cut on restore to get an relative path*/
> +		rfe.name = xstrdup(ext_id);
> +		goto ext;
> +	}
> +
>  	nsid = lookup_nsid_by_mnt_id(p->mnt_id);
>  	if (nsid == NULL) {
>  		pr_err("Can't lookup mount=%d for fd=%d path=%s\n",
> @@ -1056,12 +1065,12 @@ int dump_one_reg_file(int lfd, u32 id, const struct fd_parms *p)
>  
>  	if (check_path_remap(link, p, lfd, id, nsid))
>  		return -1;
> -
> +	rfe.name	= &link->name[1];
> +ext:
>  	rfe.id		= id;
>  	rfe.flags	= p->flags;
>  	rfe.pos		= p->pos;
>  	rfe.fown	= (FownEntry *)&p->fown;
> -	rfe.name	= &link->name[1];
>  
>  	if (S_ISREG(p->stat.st_mode) && should_check_size(rfe.flags)) {
>  		rfe.has_size = true;
> @@ -1216,11 +1225,22 @@ int open_path(struct file_desc *d,
>  	struct reg_file_info *rfi;
>  	int tmp, mntns_root;
>  	char *orig_path = NULL;
> +	char path[PATH_MAX];
>  
>  	if (inherited_fd(d, &tmp))
>  		return tmp;
>  
>  	rfi = container_of(d, struct reg_file_info, d);
> +
> +	tmp = inherit_fd_lookup_id(rfi->path);
> +	if (tmp >= 0) {
> +		mntns_root = open_pid_proc(PROC_SELF);
> +		snprintf(path, sizeof(path), "fd/%d", tmp);
> +		orig_path = rfi->path;
> +		rfi->path = path;
> +		goto ext;
> +	}
> +
>  	if (rfi->remap) {
>  		mutex_lock(ghost_file_mutex);
>  		if (rfi->remap->is_dir) {
> @@ -1262,6 +1282,7 @@ int open_path(struct file_desc *d,
>  	}
>  
>  	mntns_root = mntns_get_root_by_mnt_id(rfi->rfe->mnt_id);
> +ext:
>  	tmp = open_cb(mntns_root, rfi, arg);
>  	if (tmp < 0) {
>  		pr_perror("Can't open file %s", rfi->path);
> @@ -1303,10 +1324,10 @@ int open_path(struct file_desc *d,
>  			unlinkat(mntns_root, rfi->remap->rpath, rfi->remap->is_dir ? AT_REMOVEDIR : 0);
>  		}
>  
> -		if (orig_path)
> -			rfi->path = orig_path;
>  		mutex_unlock(ghost_file_mutex);
>  	}
> +	if (orig_path)
> +		rfi->path = orig_path;
>  
>  	if (restore_fown(tmp, rfi->rfe->fown))
>  		return -1;
>