[CRIU] [PATCH 3/6] link-remap: open link-remap files from correct mountpoints

[Andrey Vagin]

Here is a problem with ghost files. Links are created on restore, but
they can't be created on any mount point, because a mount point can be
non-root bind-mount of another one. So we need to find the root mount
and create all links there.

v2: clean up
Signed-off-by: Andrey Vagin <avagin at openvz.org>
---
 files-reg.c         | 62 ++++++++++++++++++++++++++++++++++++++++++++++-------
 include/files-reg.h |  1 +
 2 files changed, 55 insertions(+), 8 deletions(-)

diff --git a/files-reg.c b/files-reg.c
index f3a529d..de786b7 100644
--- a/files-reg.c
+++ b/files-reg.c
@@ -154,6 +154,7 @@ static int open_remap_ghost(struct reg_file_info *rfi,
 	if (!gf)
 		return -1;
 	gf->remap.path = xmalloc(PATH_MAX);
+	gf->remap.mnt_id = rfi->rfe->mnt_id;
 	if (!gf->remap.path)
 		goto err;
 
@@ -221,6 +222,7 @@ static int open_remap_linked(struct reg_file_info *rfi,
 	rm->path = rrfi->path;
 	rm->users = 0;
 	rm->is_dir = false;
+	rm->mnt_id = rfi->rfe->mnt_id;
 	rfi->remap = rm;
 	return 0;
 }
@@ -313,8 +315,12 @@ void remap_put(struct file_remap *remap)
 {
 	mutex_lock(ghost_file_mutex);
 	if (--remap->users == 0) {
+		int mntns_root;
+
 		pr_info("Unlink the ghost %s\n", remap->path);
-		unlink(remap->path);
+
+		mntns_root = mntns_get_root_by_mnt_id(remap->mnt_id);
+		unlinkat(mntns_root, remap->path, 0);
 	}
 	mutex_unlock(ghost_file_mutex);
 }
@@ -669,7 +675,48 @@ const struct fdtype_ops regfile_dump_ops = {
 
 static inline int rfi_remap(struct reg_file_info *rfi)
 {
-	return link(rfi->remap->path, rfi->path);
+	struct mount_info *mi, *rmi, *tmi;
+	int off, roff;
+	char path[PATH_MAX], rpath[PATH_MAX];
+	int mntns_root;
+
+	mi = lookup_mnt_id(rfi->rfe->mnt_id);
+
+	if (mi == NULL) {
+		mntns_root = mntns_get_root_by_mnt_id(-1);
+		return linkat(mntns_root, rfi->remap->path, mntns_root, rfi->path, 0);
+	}
+
+	/*
+	 * mi->mountpoint	./zdtm/live/static/mntns_link_ghost.test/1
+	 * + mi->rst_off	/zdtm/live/static/mntns_link_ghost.test/1
+	 * rfi->path		zdtm/live/static/mntns_link_ghost.test/1/F (deleted)
+	 */
+	rmi = lookup_mnt_id(rfi->remap->mnt_id);
+	off = strlen(mi->ns_mountpoint + 1);
+	roff = strlen(rmi->ns_mountpoint + 1);
+
+	/* Find the lowest common bind-mount */
+	for (tmi = mi; tmi->bind; tmi = tmi->bind);
+
+	/* Create paths relative to this mount.
+	 * Absolute path to the mount point + difference between source
+	 * and destination roots + path relative to the mountpoint.
+	 */
+	snprintf(path, sizeof(path), "%s/%s/%s",
+				tmi->ns_mountpoint + 1,
+				mi->root + strlen(tmi->root),
+				rfi->path + off);
+	snprintf(rpath, sizeof(rpath), "%s/%s/%s",
+				tmi->ns_mountpoint + 1,
+				rmi->root + strlen(tmi->root),
+				rfi->remap->path + roff);
+
+	pr_debug("%d: Link %s -> %s\n", tmi->mnt_id, path, rpath);
+
+	mntns_root = mntns_get_root_by_mnt_id(tmi->mnt_id);
+
+	return linkat(mntns_root, rpath, mntns_root, path, 0);
 }
 
 int open_path(struct file_desc *d,
@@ -752,16 +799,15 @@ int open_path(struct file_desc *d,
 	}
 
 	if (rfi->remap) {
-		if (!rfi->remap->is_dir)
-			unlink(rfi->path);
+		if (!rfi->remap->is_dir) {
+			unlinkat(mntns_root, rfi->path, 0);
+		}
 
 		BUG_ON(!rfi->remap->users);
 		if (--rfi->remap->users == 0) {
 			pr_info("Unlink the ghost %s\n", rfi->remap->path);
-			if (rfi->remap->is_dir)
-				rmdir(rfi->remap->path);
-			else
-				unlink(rfi->remap->path);
+			mntns_root = mntns_get_root_by_mnt_id(rfi->remap->mnt_id);
+			unlinkat(mntns_root, rfi->remap->path, rfi->remap->is_dir ? AT_REMOVEDIR : 0);
 		}
 
 		if (orig_path)
diff --git a/include/files-reg.h b/include/files-reg.h
index b4a7367..bc5f5a7 100644
--- a/include/files-reg.h
+++ b/include/files-reg.h
@@ -14,6 +14,7 @@ struct fd_parms;
 struct file_remap {
 	char *path;
 	bool is_dir;
+	int  mnt_id;
 	unsigned int users;
 };
 
-- 
1.8.5.3