Merge branch 'linus' into timers/core

Reason: Further posix_cpu_timer patches depend on mainline changes

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 911 insertions, 0 deletions

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
new file mode 100644
index 00000000000..d5114db7045
--- /dev/null
+++ b/fs/ceph/snap.c
@@ -0,0 +1,911 @@
+#include "ceph_debug.h"
+
+#include <linux/sort.h>
+#include <linux/slab.h>
+
+#include "super.h"
+#include "decode.h"
+
+/*
+ * Snapshots in ceph are driven in large part by cooperation from the
+ * client.  In contrast to local file systems or file servers that
+ * implement snapshots at a single point in the system, ceph's
+ * distributed access to storage requires clients to help decide
+ * whether a write logically occurs before or after a recently created
+ * snapshot.
+ *
+ * This provides a perfect instantanous client-wide snapshot.  Between
+ * clients, however, snapshots may appear to be applied at slightly
+ * different points in time, depending on delays in delivering the
+ * snapshot notification.
+ *
+ * Snapshots are _not_ file system-wide.  Instead, each snapshot
+ * applies to the subdirectory nested beneath some directory.  This
+ * effectively divides the hierarchy into multiple "realms," where all
+ * of the files contained by each realm share the same set of
+ * snapshots.  An individual realm's snap set contains snapshots
+ * explicitly created on that realm, as well as any snaps in its
+ * parent's snap set _after_ the point at which the parent became it's
+ * parent (due to, say, a rename).  Similarly, snaps from prior parents
+ * during the time intervals during which they were the parent are included.
+ *
+ * The client is spared most of this detail, fortunately... it must only
+ * maintains a hierarchy of realms reflecting the current parent/child
+ * realm relationship, and for each realm has an explicit list of snaps
+ * inherited from prior parents.
+ *
+ * A snap_realm struct is maintained for realms containing every inode
+ * with an open cap in the system.  (The needed snap realm information is
+ * provided by the MDS whenever a cap is issued, i.e., on open.)  A 'seq'
+ * version number is used to ensure that as realm parameters change (new
+ * snapshot, new parent, etc.) the client's realm hierarchy is updated.
+ *
+ * The realm hierarchy drives the generation of a 'snap context' for each
+ * realm, which simply lists the resulting set of snaps for the realm.  This
+ * is attached to any writes sent to OSDs.
+ */
+/*
+ * Unfortunately error handling is a bit mixed here.  If we get a snap
+ * update, but don't have enough memory to update our realm hierarchy,
+ * it's not clear what we can do about it (besides complaining to the
+ * console).
+ */
+
+
+/*
+ * increase ref count for the realm
+ *
+ * caller must hold snap_rwsem for write.
+ */
+void ceph_get_snap_realm(struct ceph_mds_client *mdsc,
+			 struct ceph_snap_realm *realm)
+{
+	dout("get_realm %p %d -> %d\n", realm,
+	     atomic_read(&realm->nref), atomic_read(&realm->nref)+1);
+	/*
+	 * since we _only_ increment realm refs or empty the empty
+	 * list with snap_rwsem held, adjusting the empty list here is
+	 * safe.  we do need to protect against concurrent empty list
+	 * additions, however.
+	 */
+	if (atomic_read(&realm->nref) == 0) {
+		spin_lock(&mdsc->snap_empty_lock);
+		list_del_init(&realm->empty_item);
+		spin_unlock(&mdsc->snap_empty_lock);
+	}
+
+	atomic_inc(&realm->nref);
+}
+
+static void __insert_snap_realm(struct rb_root *root,
+				struct ceph_snap_realm *new)
+{
+	struct rb_node **p = &root->rb_node;
+	struct rb_node *parent = NULL;
+	struct ceph_snap_realm *r = NULL;
+
+	while (*p) {
+		parent = *p;
+		r = rb_entry(parent, struct ceph_snap_realm, node);
+		if (new->ino < r->ino)
+			p = &(*p)->rb_left;
+		else if (new->ino > r->ino)
+			p = &(*p)->rb_right;
+		else
+			BUG();
+	}
+
+	rb_link_node(&new->node, parent, p);
+	rb_insert_color(&new->node, root);
+}
+
+/*
+ * create and get the realm rooted at @ino and bump its ref count.
+ *
+ * caller must hold snap_rwsem for write.
+ */
+static struct ceph_snap_realm *ceph_create_snap_realm(
+	struct ceph_mds_client *mdsc,
+	u64 ino)
+{
+	struct ceph_snap_realm *realm;
+
+	realm = kzalloc(sizeof(*realm), GFP_NOFS);
+	if (!realm)
+		return ERR_PTR(-ENOMEM);
+
+	atomic_set(&realm->nref, 0);    /* tree does not take a ref */
+	realm->ino = ino;
+	INIT_LIST_HEAD(&realm->children);
+	INIT_LIST_HEAD(&realm->child_item);
+	INIT_LIST_HEAD(&realm->empty_item);
+	INIT_LIST_HEAD(&realm->inodes_with_caps);
+	spin_lock_init(&realm->inodes_with_caps_lock);
+	__insert_snap_realm(&mdsc->snap_realms, realm);
+	dout("create_snap_realm %llx %p\n", realm->ino, realm);
+	return realm;
+}
+
+/*
+ * lookup the realm rooted at @ino.
+ *
+ * caller must hold snap_rwsem for write.
+ */
+struct ceph_snap_realm *ceph_lookup_snap_realm(struct ceph_mds_client *mdsc,
+					       u64 ino)
+{
+	struct rb_node *n = mdsc->snap_realms.rb_node;
+	struct ceph_snap_realm *r;
+
+	while (n) {
+		r = rb_entry(n, struct ceph_snap_realm, node);
+		if (ino < r->ino)
+			n = n->rb_left;
+		else if (ino > r->ino)
+			n = n->rb_right;
+		else {
+			dout("lookup_snap_realm %llx %p\n", r->ino, r);
+			return r;
+		}
+	}
+	return NULL;
+}
+
+static void __put_snap_realm(struct ceph_mds_client *mdsc,
+			     struct ceph_snap_realm *realm);
+
+/*
+ * called with snap_rwsem (write)
+ */
+static void __destroy_snap_realm(struct ceph_mds_client *mdsc,
+				 struct ceph_snap_realm *realm)
+{
+	dout("__destroy_snap_realm %p %llx\n", realm, realm->ino);
+
+	rb_erase(&realm->node, &mdsc->snap_realms);
+
+	if (realm->parent) {
+		list_del_init(&realm->child_item);
+		__put_snap_realm(mdsc, realm->parent);
+	}
+
+	kfree(realm->prior_parent_snaps);
+	kfree(realm->snaps);
+	ceph_put_snap_context(realm->cached_context);
+	kfree(realm);
+}
+
+/*
+ * caller holds snap_rwsem (write)
+ */
+static void __put_snap_realm(struct ceph_mds_client *mdsc,
+			     struct ceph_snap_realm *realm)
+{
+	dout("__put_snap_realm %llx %p %d -> %d\n", realm->ino, realm,
+	     atomic_read(&realm->nref), atomic_read(&realm->nref)-1);
+	if (atomic_dec_and_test(&realm->nref))
+		__destroy_snap_realm(mdsc, realm);
+}
+
+/*
+ * caller needn't hold any locks
+ */
+void ceph_put_snap_realm(struct ceph_mds_client *mdsc,
+			 struct ceph_snap_realm *realm)
+{
+	dout("put_snap_realm %llx %p %d -> %d\n", realm->ino, realm,
+	     atomic_read(&realm->nref), atomic_read(&realm->nref)-1);
+	if (!atomic_dec_and_test(&realm->nref))
+		return;
+
+	if (down_write_trylock(&mdsc->snap_rwsem)) {
+		__destroy_snap_realm(mdsc, realm);
+		up_write(&mdsc->snap_rwsem);
+	} else {
+		spin_lock(&mdsc->snap_empty_lock);
+		list_add(&mdsc->snap_empty, &realm->empty_item);
+		spin_unlock(&mdsc->snap_empty_lock);
+	}
+}
+
+/*
+ * Clean up any realms whose ref counts have dropped to zero.  Note
+ * that this does not include realms who were created but not yet
+ * used.
+ *
+ * Called under snap_rwsem (write)
+ */
+static void __cleanup_empty_realms(struct ceph_mds_client *mdsc)
+{
+	struct ceph_snap_realm *realm;
+
+	spin_lock(&mdsc->snap_empty_lock);
+	while (!list_empty(&mdsc->snap_empty)) {
+		realm = list_first_entry(&mdsc->snap_empty,
+				   struct ceph_snap_realm, empty_item);
+		list_del(&realm->empty_item);
+		spin_unlock(&mdsc->snap_empty_lock);
+		__destroy_snap_realm(mdsc, realm);
+		spin_lock(&mdsc->snap_empty_lock);
+	}
+	spin_unlock(&mdsc->snap_empty_lock);
+}
+
+void ceph_cleanup_empty_realms(struct ceph_mds_client *mdsc)
+{
+	down_write(&mdsc->snap_rwsem);
+	__cleanup_empty_realms(mdsc);
+	up_write(&mdsc->snap_rwsem);
+}
+
+/*
+ * adjust the parent realm of a given @realm.  adjust child list, and parent
+ * pointers, and ref counts appropriately.
+ *
+ * return true if parent was changed, 0 if unchanged, <0 on error.
+ *
+ * caller must hold snap_rwsem for write.
+ */
+static int adjust_snap_realm_parent(struct ceph_mds_client *mdsc,
+				    struct ceph_snap_realm *realm,
+				    u64 parentino)
+{
+	struct ceph_snap_realm *parent;
+
+	if (realm->parent_ino == parentino)
+		return 0;
+
+	parent = ceph_lookup_snap_realm(mdsc, parentino);
+	if (!parent) {
+		parent = ceph_create_snap_realm(mdsc, parentino);
+		if (IS_ERR(parent))
+			return PTR_ERR(parent);
+	}
+	dout("adjust_snap_realm_parent %llx %p: %llx %p -> %llx %p\n",
+	     realm->ino, realm, realm->parent_ino, realm->parent,
+	     parentino, parent);
+	if (realm->parent) {
+		list_del_init(&realm->child_item);
+		ceph_put_snap_realm(mdsc, realm->parent);
+	}
+	realm->parent_ino = parentino;
+	realm->parent = parent;
+	ceph_get_snap_realm(mdsc, parent);
+	list_add(&realm->child_item, &parent->children);
+	return 1;
+}
+
+
+static int cmpu64_rev(const void *a, const void *b)
+{
+	if (*(u64 *)a < *(u64 *)b)
+		return 1;
+	if (*(u64 *)a > *(u64 *)b)
+		return -1;
+	return 0;
+}
+
+/*
+ * build the snap context for a given realm.
+ */
+static int build_snap_context(struct ceph_snap_realm *realm)
+{
+	struct ceph_snap_realm *parent = realm->parent;
+	struct ceph_snap_context *snapc;
+	int err = 0;
+	int i;
+	int num = realm->num_prior_parent_snaps + realm->num_snaps;
+
+	/*
+	 * build parent context, if it hasn't been built.
+	 * conservatively estimate that all parent snaps might be
+	 * included by us.
+	 */
+	if (parent) {
+		if (!parent->cached_context) {
+			err = build_snap_context(parent);
+			if (err)
+				goto fail;
+		}
+		num += parent->cached_context->num_snaps;
+	}
+
+	/* do i actually need to update?  not if my context seq
+	   matches realm seq, and my parents' does to.  (this works
+	   because we rebuild_snap_realms() works _downward_ in
+	   hierarchy after each update.) */
+	if (realm->cached_context &&
+	    realm->cached_context->seq == realm->seq &&
+	    (!parent ||
+	     realm->cached_context->seq >= parent->cached_context->seq)) {
+		dout("build_snap_context %llx %p: %p seq %lld (%d snaps)"
+		     " (unchanged)\n",
+		     realm->ino, realm, realm->cached_context,
+		     realm->cached_context->seq,
+		     realm->cached_context->num_snaps);
+		return 0;
+	}
+
+	/* alloc new snap context */
+	err = -ENOMEM;
+	if (num > ULONG_MAX / sizeof(u64) - sizeof(*snapc))
+		goto fail;
+	snapc = kzalloc(sizeof(*snapc) + num*sizeof(u64), GFP_NOFS);
+	if (!snapc)
+		goto fail;
+	atomic_set(&snapc->nref, 1);
+
+	/* build (reverse sorted) snap vector */
+	num = 0;
+	snapc->seq = realm->seq;
+	if (parent) {
+		/* include any of parent's snaps occuring _after_ my
+		   parent became my parent */
+		for (i = 0; i < parent->cached_context->num_snaps; i++)
+			if (parent->cached_context->snaps[i] >=
+			    realm->parent_since)
+				snapc->snaps[num++] =
+					parent->cached_context->snaps[i];
+		if (parent->cached_context->seq > snapc->seq)
+			snapc->seq = parent->cached_context->seq;
+	}
+	memcpy(snapc->snaps + num, realm->snaps,
+	       sizeof(u64)*realm->num_snaps);
+	num += realm->num_snaps;
+	memcpy(snapc->snaps + num, realm->prior_parent_snaps,
+	       sizeof(u64)*realm->num_prior_parent_snaps);
+	num += realm->num_prior_parent_snaps;
+
+	sort(snapc->snaps, num, sizeof(u64), cmpu64_rev, NULL);
+	snapc->num_snaps = num;
+	dout("build_snap_context %llx %p: %p seq %lld (%d snaps)\n",
+	     realm->ino, realm, snapc, snapc->seq, snapc->num_snaps);
+
+	if (realm->cached_context)
+		ceph_put_snap_context(realm->cached_context);
+	realm->cached_context = snapc;
+	return 0;
+
+fail:
+	/*
+	 * if we fail, clear old (incorrect) cached_context... hopefully
+	 * we'll have better luck building it later
+	 */
+	if (realm->cached_context) {
+		ceph_put_snap_context(realm->cached_context);
+		realm->cached_context = NULL;
+	}
+	pr_err("build_snap_context %llx %p fail %d\n", realm->ino,
+	       realm, err);
+	return err;
+}
+
+/*
+ * rebuild snap context for the given realm and all of its children.
+ */
+static void rebuild_snap_realms(struct ceph_snap_realm *realm)
+{
+	struct ceph_snap_realm *child;
+
+	dout("rebuild_snap_realms %llx %p\n", realm->ino, realm);
+	build_snap_context(realm);
+
+	list_for_each_entry(child, &realm->children, child_item)
+		rebuild_snap_realms(child);
+}
+
+
+/*
+ * helper to allocate and decode an array of snapids.  free prior
+ * instance, if any.
+ */
+static int dup_array(u64 **dst, __le64 *src, int num)
+{
+	int i;
+
+	kfree(*dst);
+	if (num) {
+		*dst = kcalloc(num, sizeof(u64), GFP_NOFS);
+		if (!*dst)
+			return -ENOMEM;
+		for (i = 0; i < num; i++)
+			(*dst)[i] = get_unaligned_le64(src + i);
+	} else {
+		*dst = NULL;
+	}
+	return 0;
+}
+
+
+/*
+ * When a snapshot is applied, the size/mtime inode metadata is queued
+ * in a ceph_cap_snap (one for each snapshot) until writeback
+ * completes and the metadata can be flushed back to the MDS.
+ *
+ * However, if a (sync) write is currently in-progress when we apply
+ * the snapshot, we have to wait until the write succeeds or fails
+ * (and a final size/mtime is known).  In this case the
+ * cap_snap->writing = 1, and is said to be "pending."  When the write
+ * finishes, we __ceph_finish_cap_snap().
+ *
+ * Caller must hold snap_rwsem for read (i.e., the realm topology won't
+ * change).
+ */
+void ceph_queue_cap_snap(struct ceph_inode_info *ci)
+{
+	struct inode *inode = &ci->vfs_inode;
+	struct ceph_cap_snap *capsnap;
+	int used;
+
+	capsnap = kzalloc(sizeof(*capsnap), GFP_NOFS);
+	if (!capsnap) {
+		pr_err("ENOMEM allocating ceph_cap_snap on %p\n", inode);
+		return;
+	}
+
+	spin_lock(&inode->i_lock);
+	used = __ceph_caps_used(ci);
+	if (__ceph_have_pending_cap_snap(ci)) {
+		/* there is no point in queuing multiple "pending" cap_snaps,
+		   as no new writes are allowed to start when pending, so any
+		   writes in progress now were started before the previous
+		   cap_snap.  lucky us. */
+		dout("queue_cap_snap %p already pending\n", inode);
+		kfree(capsnap);
+	} else if (ci->i_wrbuffer_ref_head || (used & CEPH_CAP_FILE_WR)) {
+		struct ceph_snap_context *snapc = ci->i_head_snapc;
+
+		igrab(inode);
+
+		atomic_set(&capsnap->nref, 1);
+		capsnap->ci = ci;
+		INIT_LIST_HEAD(&capsnap->ci_item);
+		INIT_LIST_HEAD(&capsnap->flushing_item);
+
+		capsnap->follows = snapc->seq - 1;
+		capsnap->issued = __ceph_caps_issued(ci, NULL);
+		capsnap->dirty = __ceph_caps_dirty(ci);
+
+		capsnap->mode = inode->i_mode;
+		capsnap->uid = inode->i_uid;
+		capsnap->gid = inode->i_gid;
+
+		/* fixme? */
+		capsnap->xattr_blob = NULL;
+		capsnap->xattr_len = 0;
+
+		/* dirty page count moved from _head to this cap_snap;
+		   all subsequent writes page dirties occur _after_ this
+		   snapshot. */
+		capsnap->dirty_pages = ci->i_wrbuffer_ref_head;
+		ci->i_wrbuffer_ref_head = 0;
+		capsnap->context = snapc;
+		ci->i_head_snapc = NULL;
+		list_add_tail(&capsnap->ci_item, &ci->i_cap_snaps);
+
+		if (used & CEPH_CAP_FILE_WR) {
+			dout("queue_cap_snap %p cap_snap %p snapc %p"
+			     " seq %llu used WR, now pending\n", inode,
+			     capsnap, snapc, snapc->seq);
+			capsnap->writing = 1;
+		} else {
+			/* note mtime, size NOW. */
+			__ceph_finish_cap_snap(ci, capsnap);
+		}
+	} else {
+		dout("queue_cap_snap %p nothing dirty|writing\n", inode);
+		kfree(capsnap);
+	}
+
+	spin_unlock(&inode->i_lock);
+}
+
+/*
+ * Finalize the size, mtime for a cap_snap.. that is, settle on final values
+ * to be used for the snapshot, to be flushed back to the mds.
+ *
+ * If capsnap can now be flushed, add to snap_flush list, and return 1.
+ *
+ * Caller must hold i_lock.
+ */
+int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
+			    struct ceph_cap_snap *capsnap)
+{
+	struct inode *inode = &ci->vfs_inode;
+	struct ceph_mds_client *mdsc = &ceph_client(inode->i_sb)->mdsc;
+
+	BUG_ON(capsnap->writing);
+	capsnap->size = inode->i_size;
+	capsnap->mtime = inode->i_mtime;
+	capsnap->atime = inode->i_atime;
+	capsnap->ctime = inode->i_ctime;
+	capsnap->time_warp_seq = ci->i_time_warp_seq;
+	if (capsnap->dirty_pages) {
+		dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu "
+		     "still has %d dirty pages\n", inode, capsnap,
+		     capsnap->context, capsnap->context->seq,
+		     ceph_cap_string(capsnap->dirty), capsnap->size,
+		     capsnap->dirty_pages);
+		return 0;
+	}
+	dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu\n",
+	     inode, capsnap, capsnap->context,
+	     capsnap->context->seq, ceph_cap_string(capsnap->dirty),
+	     capsnap->size);
+
+	spin_lock(&mdsc->snap_flush_lock);
+	list_add_tail(&ci->i_snap_flush_item, &mdsc->snap_flush_list);
+	spin_unlock(&mdsc->snap_flush_lock);
+	return 1;  /* caller may want to ceph_flush_snaps */
+}
+
+
+/*
+ * Parse and apply a snapblob "snap trace" from the MDS.  This specifies
+ * the snap realm parameters from a given realm and all of its ancestors,
+ * up to the root.
+ *
+ * Caller must hold snap_rwsem for write.
+ */
+int ceph_update_snap_trace(struct ceph_mds_client *mdsc,
+			   void *p, void *e, bool deletion)
+{
+	struct ceph_mds_snap_realm *ri;    /* encoded */
+	__le64 *snaps;                     /* encoded */
+	__le64 *prior_parent_snaps;        /* encoded */
+	struct ceph_snap_realm *realm;
+	int invalidate = 0;
+	int err = -ENOMEM;
+
+	dout("update_snap_trace deletion=%d\n", deletion);
+more:
+	ceph_decode_need(&p, e, sizeof(*ri), bad);
+	ri = p;
+	p += sizeof(*ri);
+	ceph_decode_need(&p, e, sizeof(u64)*(le32_to_cpu(ri->num_snaps) +
+			    le32_to_cpu(ri->num_prior_parent_snaps)), bad);
+	snaps = p;
+	p += sizeof(u64) * le32_to_cpu(ri->num_snaps);
+	prior_parent_snaps = p;
+	p += sizeof(u64) * le32_to_cpu(ri->num_prior_parent_snaps);
+
+	realm = ceph_lookup_snap_realm(mdsc, le64_to_cpu(ri->ino));
+	if (!realm) {
+		realm = ceph_create_snap_realm(mdsc, le64_to_cpu(ri->ino));
+		if (IS_ERR(realm)) {
+			err = PTR_ERR(realm);
+			goto fail;
+		}
+	}
+
+	if (le64_to_cpu(ri->seq) > realm->seq) {
+		dout("update_snap_trace updating %llx %p %lld -> %lld\n",
+		     realm->ino, realm, realm->seq, le64_to_cpu(ri->seq));
+		/*
+		 * if the realm seq has changed, queue a cap_snap for every
+		 * inode with open caps.  we do this _before_ we update
+		 * the realm info so that we prepare for writeback under the
+		 * _previous_ snap context.
+		 *
+		 * ...unless it's a snap deletion!
+		 */
+		if (!deletion) {
+			struct ceph_inode_info *ci;
+			struct inode *lastinode = NULL;
+
+			spin_lock(&realm->inodes_with_caps_lock);
+			list_for_each_entry(ci, &realm->inodes_with_caps,
+					    i_snap_realm_item) {
+				struct inode *inode = igrab(&ci->vfs_inode);
+				if (!inode)
+					continue;
+				spin_unlock(&realm->inodes_with_caps_lock);
+				if (lastinode)
+					iput(lastinode);
+				lastinode = inode;
+				ceph_queue_cap_snap(ci);
+				spin_lock(&realm->inodes_with_caps_lock);
+			}
+			spin_unlock(&realm->inodes_with_caps_lock);
+			if (lastinode)
+				iput(lastinode);
+			dout("update_snap_trace cap_snaps queued\n");
+		}
+
+	} else {
+		dout("update_snap_trace %llx %p seq %lld unchanged\n",
+		     realm->ino, realm, realm->seq);
+	}
+
+	/* ensure the parent is correct */
+	err = adjust_snap_realm_parent(mdsc, realm, le64_to_cpu(ri->parent));
+	if (err < 0)
+		goto fail;
+	invalidate += err;
+
+	if (le64_to_cpu(ri->seq) > realm->seq) {
+		/* update realm parameters, snap lists */
+		realm->seq = le64_to_cpu(ri->seq);
+		realm->created = le64_to_cpu(ri->created);
+		realm->parent_since = le64_to_cpu(ri->parent_since);
+
+		realm->num_snaps = le32_to_cpu(ri->num_snaps);
+		err = dup_array(&realm->snaps, snaps, realm->num_snaps);
+		if (err < 0)
+			goto fail;
+
+		realm->num_prior_parent_snaps =
+			le32_to_cpu(ri->num_prior_parent_snaps);
+		err = dup_array(&realm->prior_parent_snaps, prior_parent_snaps,
+				realm->num_prior_parent_snaps);
+		if (err < 0)
+			goto fail;
+
+		invalidate = 1;
+	} else if (!realm->cached_context) {
+		invalidate = 1;
+	}
+
+	dout("done with %llx %p, invalidated=%d, %p %p\n", realm->ino,
+	     realm, invalidate, p, e);
+
+	if (p < e)
+		goto more;
+
+	/* invalidate when we reach the _end_ (root) of the trace */
+	if (invalidate)
+		rebuild_snap_realms(realm);
+
+	__cleanup_empty_realms(mdsc);
+	return 0;
+
+bad:
+	err = -EINVAL;
+fail:
+	pr_err("update_snap_trace error %d\n", err);
+	return err;
+}
+
+
+/*
+ * Send any cap_snaps that are queued for flush.  Try to carry
+ * s_mutex across multiple snap flushes to avoid locking overhead.
+ *
+ * Caller holds no locks.
+ */
+static void flush_snaps(struct ceph_mds_client *mdsc)
+{
+	struct ceph_inode_info *ci;
+	struct inode *inode;
+	struct ceph_mds_session *session = NULL;
+
+	dout("flush_snaps\n");
+	spin_lock(&mdsc->snap_flush_lock);
+	while (!list_empty(&mdsc->snap_flush_list)) {
+		ci = list_first_entry(&mdsc->snap_flush_list,
+				struct ceph_inode_info, i_snap_flush_item);
+		inode = &ci->vfs_inode;
+		igrab(inode);
+		spin_unlock(&mdsc->snap_flush_lock);
+		spin_lock(&inode->i_lock);
+		__ceph_flush_snaps(ci, &session);
+		spin_unlock(&inode->i_lock);
+		iput(inode);
+		spin_lock(&mdsc->snap_flush_lock);
+	}
+	spin_unlock(&mdsc->snap_flush_lock);
+
+	if (session) {
+		mutex_unlock(&session->s_mutex);
+		ceph_put_mds_session(session);
+	}
+	dout("flush_snaps done\n");
+}
+
+
+/*
+ * Handle a snap notification from the MDS.
+ *
+ * This can take two basic forms: the simplest is just a snap creation
+ * or deletion notification on an existing realm.  This should update the
+ * realm and its children.
+ *
+ * The more difficult case is realm creation, due to snap creation at a
+ * new point in the file hierarchy, or due to a rename that moves a file or
+ * directory into another realm.
+ */
+void ceph_handle_snap(struct ceph_mds_client *mdsc,
+		      struct ceph_mds_session *session,
+		      struct ceph_msg *msg)
+{
+	struct super_block *sb = mdsc->client->sb;
+	int mds = session->s_mds;
+	u64 split;
+	int op;
+	int trace_len;
+	struct ceph_snap_realm *realm = NULL;
+	void *p = msg->front.iov_base;
+	void *e = p + msg->front.iov_len;
+	struct ceph_mds_snap_head *h;
+	int num_split_inos, num_split_realms;
+	__le64 *split_inos = NULL, *split_realms = NULL;
+	int i;
+	int locked_rwsem = 0;
+
+	/* decode */
+	if (msg->front.iov_len < sizeof(*h))
+		goto bad;
+	h = p;
+	op = le32_to_cpu(h->op);
+	split = le64_to_cpu(h->split);   /* non-zero if we are splitting an
+					  * existing realm */
+	num_split_inos = le32_to_cpu(h->num_split_inos);
+	num_split_realms = le32_to_cpu(h->num_split_realms);
+	trace_len = le32_to_cpu(h->trace_len);
+	p += sizeof(*h);
+
+	dout("handle_snap from mds%d op %s split %llx tracelen %d\n", mds,
+	     ceph_snap_op_name(op), split, trace_len);
+
+	mutex_lock(&session->s_mutex);
+	session->s_seq++;
+	mutex_unlock(&session->s_mutex);
+
+	down_write(&mdsc->snap_rwsem);
+	locked_rwsem = 1;
+
+	if (op == CEPH_SNAP_OP_SPLIT) {
+		struct ceph_mds_snap_realm *ri;
+
+		/*
+		 * A "split" breaks part of an existing realm off into
+		 * a new realm.  The MDS provides a list of inodes
+		 * (with caps) and child realms that belong to the new
+		 * child.
+		 */
+		split_inos = p;
+		p += sizeof(u64) * num_split_inos;
+		split_realms = p;
+		p += sizeof(u64) * num_split_realms;
+		ceph_decode_need(&p, e, sizeof(*ri), bad);
+		/* we will peek at realm info here, but will _not_
+		 * advance p, as the realm update will occur below in
+		 * ceph_update_snap_trace. */
+		ri = p;
+
+		realm = ceph_lookup_snap_realm(mdsc, split);
+		if (!realm) {
+			realm = ceph_create_snap_realm(mdsc, split);
+			if (IS_ERR(realm))
+				goto out;
+		}
+		ceph_get_snap_realm(mdsc, realm);
+
+		dout("splitting snap_realm %llx %p\n", realm->ino, realm);
+		for (i = 0; i < num_split_inos; i++) {
+			struct ceph_vino vino = {
+				.ino = le64_to_cpu(split_inos[i]),
+				.snap = CEPH_NOSNAP,
+			};
+			struct inode *inode = ceph_find_inode(sb, vino);
+			struct ceph_inode_info *ci;
+
+			if (!inode)
+				continue;
+			ci = ceph_inode(inode);
+
+			spin_lock(&inode->i_lock);
+			if (!ci->i_snap_realm)
+				goto skip_inode;
+			/*
+			 * If this inode belongs to a realm that was
+			 * created after our new realm, we experienced
+			 * a race (due to another split notifications
+			 * arriving from a different MDS).  So skip
+			 * this inode.
+			 */
+			if (ci->i_snap_realm->created >
+			    le64_to_cpu(ri->created)) {
+				dout(" leaving %p in newer realm %llx %p\n",
+				     inode, ci->i_snap_realm->ino,
+				     ci->i_snap_realm);
+				goto skip_inode;
+			}
+			dout(" will move %p to split realm %llx %p\n",
+			     inode, realm->ino, realm);
+			/*
+			 * Remove the inode from the realm's inode
+			 * list, but don't add it to the new realm
+			 * yet.  We don't want the cap_snap to be
+			 * queued (again) by ceph_update_snap_trace()
+			 * below.  Queue it _now_, under the old context.
+			 */
+			spin_lock(&realm->inodes_with_caps_lock);
+			list_del_init(&ci->i_snap_realm_item);
+			spin_unlock(&realm->inodes_with_caps_lock);
+			spin_unlock(&inode->i_lock);
+
+			ceph_queue_cap_snap(ci);
+
+			iput(inode);
+			continue;
+
+skip_inode:
+			spin_unlock(&inode->i_lock);
+			iput(inode);
+		}
+
+		/* we may have taken some of the old realm's children. */
+		for (i = 0; i < num_split_realms; i++) {
+			struct ceph_snap_realm *child =
+				ceph_lookup_snap_realm(mdsc,
+					   le64_to_cpu(split_realms[i]));
+			if (!child)
+				continue;
+			adjust_snap_realm_parent(mdsc, child, realm->ino);
+		}
+	}
+
+	/*
+	 * update using the provided snap trace. if we are deleting a
+	 * snap, we can avoid queueing cap_snaps.
+	 */
+	ceph_update_snap_trace(mdsc, p, e,
+			       op == CEPH_SNAP_OP_DESTROY);
+
+	if (op == CEPH_SNAP_OP_SPLIT) {
+		/*
+		 * ok, _now_ add the inodes into the new realm.
+		 */
+		for (i = 0; i < num_split_inos; i++) {
+			struct ceph_vino vino = {
+				.ino = le64_to_cpu(split_inos[i]),
+				.snap = CEPH_NOSNAP,
+			};
+			struct inode *inode = ceph_find_inode(sb, vino);
+			struct ceph_inode_info *ci;
+
+			if (!inode)
+				continue;
+			ci = ceph_inode(inode);
+			spin_lock(&inode->i_lock);
+			if (list_empty(&ci->i_snap_realm_item)) {
+				struct ceph_snap_realm *oldrealm =
+					ci->i_snap_realm;
+
+				dout(" moving %p to split realm %llx %p\n",
+				     inode, realm->ino, realm);
+				spin_lock(&realm->inodes_with_caps_lock);
+				list_add(&ci->i_snap_realm_item,
+					 &realm->inodes_with_caps);
+				ci->i_snap_realm = realm;
+				spin_unlock(&realm->inodes_with_caps_lock);
+				ceph_get_snap_realm(mdsc, realm);
+				ceph_put_snap_realm(mdsc, oldrealm);
+			}
+			spin_unlock(&inode->i_lock);
+			iput(inode);
+		}
+
+		/* we took a reference when we created the realm, above */
+		ceph_put_snap_realm(mdsc, realm);
+	}
+
+	__cleanup_empty_realms(mdsc);
+
+	up_write(&mdsc->snap_rwsem);
+
+	flush_snaps(mdsc);
+	return;
+
+bad:
+	pr_err("corrupt snap message from mds%d\n", mds);
+	ceph_msg_dump(msg);
+out:
+	if (locked_rwsem)
+		up_write(&mdsc->snap_rwsem);
+	return;
+}
+
+
+