[CRIU] [PATCH] link_remap: do not create excessive links for a single file

[Stanislav Kinsburskiy]

Currently criu always creates link for each file, considered as "silly-renamed".
Even in those cases, when file is opened multiple times, it creates one new
link for each occurrence.
On restore only one link file is used for all the file descriptors, sharing
this path. And only this link is removed.
The rest of the links are forgotten and abandoned on file system.
This patch fixed this mess by creating the link only iff it's unique. Or
skipping this job otherwise.

Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
---
 criu/files-reg.c |   50 ++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 44 insertions(+), 6 deletions(-)

diff --git a/criu/files-reg.c b/criu/files-reg.c
index fd36ae9..b1ad271 100644
--- a/criu/files-reg.c
+++ b/criu/files-reg.c
@@ -70,9 +70,11 @@ struct link_remap_rlb {
 	struct list_head	list;
 	struct ns_id		*mnt_ns;
 	char			*path;
+	char			*orig;
+	u32			id;
 };
 
-static int note_link_remap(char *path, struct ns_id *nsid)
+static int note_link_remap(char *path, char *orig, struct ns_id *nsid, u32 id)
 {
 	struct link_remap_rlb *rlb;
 
@@ -84,11 +86,18 @@ static int note_link_remap(char *path, struct ns_id *nsid)
 	if (!rlb->path)
 		goto err2;
 
+	rlb->orig = strdup(orig);
+	if (!rlb->orig)
+		goto err3;
+
 	rlb->mnt_ns = nsid;
+	rlb->id = id;
 	list_add(&rlb->list, &remaps);
 
 	return 0;
 
+err3:
+	xfree(rlb->path);
 err2:
 	xfree(rlb);
 err:
@@ -96,6 +105,22 @@ err:
 	return -1;
 }
 
+static int find_link_remap(char *path, struct ns_id *nsid, u32 *id)
+{
+	struct link_remap_rlb *rlb;
+
+	list_for_each_entry(rlb, &remaps, list) {
+		if (rlb->mnt_ns != nsid)
+			continue;
+		if (strcmp(rlb->orig, path))
+			continue;
+
+		*id = rlb->id;
+		return 0;
+	}
+	return -ENOENT;
+}
+
 /* Trim "a/b/c/d" to "a/b/d" */
 static int trim_last_parent(char *path)
 {
@@ -725,6 +750,7 @@ static void __rollback_link_remaps(bool do_unlink)
 		}
 
 		list_del(&rlb->list);
+		xfree(rlb->orig);
 		xfree(rlb->path);
 		xfree(rlb);
 	}
@@ -781,28 +807,40 @@ static int create_link_remap(char *path, int len, int lfd,
 		return -1;
 	}
 
-	if (note_link_remap(link_name, nsid))
+	if (note_link_remap(link_name, path, nsid, *idp))
 		return -1;
 
 	return pb_write_one(img_from_set(glob_imgset, CR_FD_REG_FILES), &rfe, PB_REG_FILE);
 }
 
-static int dump_linked_remap(char *path, int len, const struct stat *ost,
-				int lfd, u32 id, struct ns_id *nsid)
+static int dump_linked_remap_type(char *path, int len, int lfd, u32 id, struct ns_id *nsid, RemapType remap_type, bool unique)
 {
 	u32 lid;
 	RemapFilePathEntry rpe = REMAP_FILE_PATH_ENTRY__INIT;
 
-	if (create_link_remap(path, len, lfd, &lid, nsid))
-		return -1;
+	if (!find_link_remap(path, nsid, &lid)) {
+		pr_debug("Link remap for %s already exists with id %x\n",
+				path, lid);
+		if (unique)
+			return 0;
+	} else if (create_link_remap(path, len, lfd, &lid, nsid))
+			return -1;
 
 	rpe.orig_id = id;
 	rpe.remap_id = lid;
+	rpe.has_remap_type = true;
+	rpe.remap_type = remap_type;
 
 	return pb_write_one(img_from_set(glob_imgset, CR_FD_REMAP_FPATH),
 			&rpe, PB_REMAP_FPATH);
 }
 
+static int dump_linked_remap(char *path, int len, const struct stat *ost,
+				int lfd, u32 id, struct ns_id *nsid)
+{
+	return dump_linked_remap_type(path, len, lfd, id, nsid, REMAP_TYPE__LINKED, false);
+}
+
 static pid_t *dead_pids;
 static int n_dead_pids;