ceph: map snapid to anonymous bdev ID

ceph_getattr() return zero dev ID for head inodes and set dev ID to
snapid directly for snaphost inodes. This is not good because userspace
utilities may consider device ID of 0 as invalid, snapid may conflict
with other device's ID.

This patch introduces "snapids to anonymous bdev IDs" map. we create a
new mapping when we see a snapid for the first time. we trim unused
mapping after it is ilde for 5 minutes.

Link: http://tracker.ceph.com/issues/22353
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/inode.c

@@ -548,17 +548,22 @@ void ceph_destroy_inode(struct inode *inode)
 	 */
 	if (ci->i_snap_realm) {
 		struct ceph_mds_client *mdsc =
-			ceph_sb_to_client(ci->vfs_inode.i_sb)->mdsc;
-		struct ceph_snap_realm *realm = ci->i_snap_realm;
-
-		dout(" dropping residual ref to snap realm %p\n", realm);
-		spin_lock(&realm->inodes_with_caps_lock);
-		list_del_init(&ci->i_snap_realm_item);
-		ci->i_snap_realm = NULL;
-		if (realm->ino == ci->i_vino.ino)
-			realm->inode = NULL;
-		spin_unlock(&realm->inodes_with_caps_lock);
-		ceph_put_snap_realm(mdsc, realm);
+					ceph_inode_to_client(inode)->mdsc;
+		if (ceph_snap(inode) == CEPH_NOSNAP) {
+			struct ceph_snap_realm *realm = ci->i_snap_realm;
+			dout(" dropping residual ref to snap realm %p\n",
+			     realm);
+			spin_lock(&realm->inodes_with_caps_lock);
+			list_del_init(&ci->i_snap_realm_item);
+			ci->i_snap_realm = NULL;
+			if (realm->ino == ci->i_vino.ino)
+				realm->inode = NULL;
+			spin_unlock(&realm->inodes_with_caps_lock);
+			ceph_put_snap_realm(mdsc, realm);
+		} else {
+			ceph_put_snapid_map(mdsc, ci->i_snapid_map);
+			ci->i_snap_realm = NULL;
+		}
 	}
 
 	kfree(ci->i_symlink);
@@ -776,6 +781,9 @@ static int fill_inode(struct inode *inode, struct page *locked_page,
 		pool_ns = ceph_find_or_create_string(iinfo->pool_ns_data,
 						     iinfo->pool_ns_len);
 
+	if (ceph_snap(inode) != CEPH_NOSNAP && !ci->i_snapid_map)
+		ci->i_snapid_map = ceph_get_snapid_map(mdsc, ceph_snap(inode));
+
 	spin_lock(&ci->i_ceph_lock);
 
 	/*
@@ -2260,10 +2268,11 @@ int ceph_getattr(const struct path *path, struct kstat *stat,
 	if (!err) {
 		generic_fillattr(inode, stat);
 		stat->ino = ceph_translate_ino(inode->i_sb, inode->i_ino);
-		if (ceph_snap(inode) != CEPH_NOSNAP)
-			stat->dev = ceph_snap(inode);
+		if (ceph_snap(inode) == CEPH_NOSNAP)
+			stat->dev = inode->i_sb->s_dev;
 		else
-			stat->dev = 0;
+			stat->dev = ci->i_snapid_map ? ci->i_snapid_map->dev : 0;
+
 		if (S_ISDIR(inode->i_mode)) {
 			if (ceph_test_mount_opt(ceph_sb_to_client(inode->i_sb),
 						RBYTES))

fs/ceph/mds_client.c

@@ -3791,6 +3791,8 @@ static void delayed_work(struct work_struct *work)
 	dout("mdsc delayed_work\n");
 	ceph_check_delayed_caps(mdsc);
 
+	ceph_trim_snapid_map(mdsc);
+
 	mutex_lock(&mdsc->mutex);
 	renew_interval = mdsc->mdsmap->m_session_timeout >> 2;
 	renew_caps = time_after_eq(jiffies, HZ*renew_interval +
@@ -3893,6 +3895,10 @@ int ceph_mdsc_init(struct ceph_fs_client *fsc)
 	ceph_caps_init(mdsc);
 	ceph_adjust_min_caps(mdsc, fsc->min_caps);
 
+	spin_lock_init(&mdsc->snapid_map_lock);
+	mdsc->snapid_map_tree = RB_ROOT;
+	INIT_LIST_HEAD(&mdsc->snapid_map_lru);
+
 	init_rwsem(&mdsc->pool_perm_rwsem);
 	mdsc->pool_perm_tree = RB_ROOT;
 
@@ -4086,6 +4092,8 @@ void ceph_mdsc_close_sessions(struct ceph_mds_client *mdsc)
 	WARN_ON(!list_empty(&mdsc->cap_delay_list));
 	mutex_unlock(&mdsc->mutex);
 
+	ceph_cleanup_snapid_map(mdsc);
+
 	ceph_cleanup_empty_realms(mdsc);
 
 	cancel_delayed_work_sync(&mdsc->delayed_work); /* cancel timer */

fs/ceph/mds_client.h

@@ -313,6 +313,15 @@ struct ceph_pool_perm {
 	char pool_ns[];
 };
 
+struct ceph_snapid_map {
+	struct rb_node node;
+	struct list_head lru;
+	atomic_t ref;
+	u64 snap;
+	dev_t dev;
+	unsigned long last_used;
+};
+
 /*
  * mds client state
  */
@@ -390,6 +399,10 @@ struct ceph_mds_client {
 	struct list_head  dentry_lru;
 	int		  num_dentry;
 
+	spinlock_t		snapid_map_lock;
+	struct rb_root		snapid_map_tree;
+	struct list_head	snapid_map_lru;
+
 	struct rw_semaphore     pool_perm_rwsem;
 	struct rb_root		pool_perm_tree;
 

fs/ceph/snap.c

@@ -3,12 +3,13 @@
 
 #include <linux/sort.h>
 #include <linux/slab.h>
-
 #include "super.h"
 #include "mds_client.h"
-
 #include <linux/ceph/decode.h>
 
+/* unused map expires after 5 minutes */
+#define CEPH_SNAPID_MAP_TIMEOUT	(5 * 60 * HZ)
+
 /*
  * Snapshots in ceph are driven in large part by cooperation from the
  * client.  In contrast to local file systems or file servers that
@@ -989,3 +990,154 @@ out:
 		up_write(&mdsc->snap_rwsem);
 	return;
 }
+
+struct ceph_snapid_map* ceph_get_snapid_map(struct ceph_mds_client *mdsc,
+					    u64 snap)
+{
+	struct ceph_snapid_map *sm, *exist;
+	struct rb_node **p, *parent;
+	int ret;
+
+	exist = NULL;
+	spin_lock(&mdsc->snapid_map_lock);
+	p = &mdsc->snapid_map_tree.rb_node;
+	while (*p) {
+		exist = rb_entry(*p, struct ceph_snapid_map, node);
+		if (snap > exist->snap) {
+			p = &(*p)->rb_left;
+		} else if (snap < exist->snap) {
+			p = &(*p)->rb_right;
+		} else {
+			if (atomic_inc_return(&exist->ref) == 1)
+				list_del_init(&exist->lru);
+			break;
+		}
+		exist = NULL;
+	}
+	spin_unlock(&mdsc->snapid_map_lock);
+	if (exist) {
+		dout("found snapid map %llx -> %x\n", exist->snap, exist->dev);
+		return exist;
+	}
+
+	sm = kmalloc(sizeof(*sm), GFP_NOFS);
+	if (!sm)
+		return NULL;
+
+	ret = get_anon_bdev(&sm->dev);
+	if (ret < 0) {
+		kfree(sm);
+		return NULL;
+	}
+
+	INIT_LIST_HEAD(&sm->lru);
+	atomic_set(&sm->ref, 1);
+	sm->snap = snap;
+
+	exist = NULL;
+	parent = NULL;
+	p = &mdsc->snapid_map_tree.rb_node;
+	spin_lock(&mdsc->snapid_map_lock);
+	while (*p) {
+		parent = *p;
+		exist = rb_entry(*p, struct ceph_snapid_map, node);
+		if (snap > exist->snap)
+			p = &(*p)->rb_left;
+		else if (snap < exist->snap)
+			p = &(*p)->rb_right;
+		else
+			break;
+		exist = NULL;
+	}
+	if (exist) {
+		if (atomic_inc_return(&exist->ref) == 1)
+			list_del_init(&exist->lru);
+	} else {
+		rb_link_node(&sm->node, parent, p);
+		rb_insert_color(&sm->node, &mdsc->snapid_map_tree);
+	}
+	spin_unlock(&mdsc->snapid_map_lock);
+	if (exist) {
+		free_anon_bdev(sm->dev);
+		kfree(sm);
+		dout("found snapid map %llx -> %x\n", exist->snap, exist->dev);
+		return exist;
+	}
+
+	dout("create snapid map %llx -> %x\n", sm->snap, sm->dev);
+	return sm;
+}
+
+void ceph_put_snapid_map(struct ceph_mds_client* mdsc,
+			 struct ceph_snapid_map *sm)
+{
+	if (!sm)
+		return;
+	if (atomic_dec_and_lock(&sm->ref, &mdsc->snapid_map_lock)) {
+		if (!RB_EMPTY_NODE(&sm->node)) {
+			sm->last_used = jiffies;
+			list_add_tail(&sm->lru, &mdsc->snapid_map_lru);
+			spin_unlock(&mdsc->snapid_map_lock);
+		} else {
+			/* already cleaned up by
+			 * ceph_cleanup_snapid_map() */
+			spin_unlock(&mdsc->snapid_map_lock);
+			kfree(sm);
+		}
+	}
+}
+
+void ceph_trim_snapid_map(struct ceph_mds_client *mdsc)
+{
+	struct ceph_snapid_map *sm;
+	unsigned long now;
+	LIST_HEAD(to_free);
+
+	spin_lock(&mdsc->snapid_map_lock);
+	now = jiffies;
+
+	while (!list_empty(&mdsc->snapid_map_lru)) {
+		sm = list_first_entry(&mdsc->snapid_map_lru,
+				      struct ceph_snapid_map, lru);
+		if (time_after(sm->last_used + CEPH_SNAPID_MAP_TIMEOUT, now))
+			break;
+
+		rb_erase(&sm->node, &mdsc->snapid_map_tree);
+		list_move(&sm->lru, &to_free);
+	}
+	spin_unlock(&mdsc->snapid_map_lock);
+
+	while (!list_empty(&to_free)) {
+		sm = list_first_entry(&to_free, struct ceph_snapid_map, lru);
+		list_del(&sm->lru);
+		dout("trim snapid map %llx -> %x\n", sm->snap, sm->dev);
+		free_anon_bdev(sm->dev);
+		kfree(sm);
+	}
+}
+
+void ceph_cleanup_snapid_map(struct ceph_mds_client *mdsc)
+{
+	struct ceph_snapid_map *sm;
+	struct rb_node *p;
+	LIST_HEAD(to_free);
+
+	spin_lock(&mdsc->snapid_map_lock);
+	while ((p = rb_first(&mdsc->snapid_map_tree))) {
+		sm = rb_entry(p, struct ceph_snapid_map, node);
+		rb_erase(p, &mdsc->snapid_map_tree);
+		RB_CLEAR_NODE(p);
+		list_move(&sm->lru, &to_free);
+	}
+	spin_unlock(&mdsc->snapid_map_lock);
+
+	while (!list_empty(&to_free)) {
+		sm = list_first_entry(&to_free, struct ceph_snapid_map, lru);
+		list_del(&sm->lru);
+		free_anon_bdev(sm->dev);
+		if (WARN_ON_ONCE(atomic_read(&sm->ref))) {
+			pr_err("snapid map %llx -> %x still in use\n",
+			       sm->snap, sm->dev);
+		}
+	}
+}

fs/ceph/super.h

@@ -370,7 +370,10 @@ struct ceph_inode_info {
 	struct list_head i_unsafe_iops;   /* uncommitted mds inode ops */
 	spinlock_t i_unsafe_lock;
 
-	struct ceph_snap_realm *i_snap_realm; /* snap realm (if caps) */
+	union {
+		struct ceph_snap_realm *i_snap_realm; /* snap realm (if caps) */
+		struct ceph_snapid_map *i_snapid_map; /* snapid -> dev_t */
+	};
 	int i_snap_realm_counter; /* snap realm (if caps) */
 	struct list_head i_snap_realm_item;
 	struct list_head i_snap_flush_item;
@@ -837,6 +840,14 @@ extern int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
 				  struct ceph_cap_snap *capsnap);
 extern void ceph_cleanup_empty_realms(struct ceph_mds_client *mdsc);
 
+extern struct ceph_snapid_map *ceph_get_snapid_map(struct ceph_mds_client *mdsc,
+						   u64 snap);
+extern void ceph_put_snapid_map(struct ceph_mds_client* mdsc,
+				struct ceph_snapid_map *sm);
+extern void ceph_trim_snapid_map(struct ceph_mds_client *mdsc);
+extern void ceph_cleanup_snapid_map(struct ceph_mds_client *mdsc);
+
+
 /*
  * a cap_snap is "pending" if it is still awaiting an in-progress
  * sync write (that may/may not still update size, mtime, etc.).