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

[Kirill Tkhai]

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 = '_';
 }
 
 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);
 
 	if (old_ns >= 0) {
 		if (setns(old_ns, CLONE_NEWNS) < 0)