#include <linux/ceph/ceph_debug.h>
  
  #include <linux/sort.h>
  #include <linux/slab.h>
  
  #include "super.h"
  #include "mds_client.h"
  
  #include <linux/ceph/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
  ", 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->dirty_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
  ", 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
  ", 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
  ", 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
  ", 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
  ", 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(&realm->empty_item, &mdsc->snap_empty);
  		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
  ",
  	     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;
  	u32 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 (%u snaps)"
  		     " (unchanged)
  ",
  		     realm->ino, realm, realm->cached_context,
  		     realm->cached_context->seq,
  		     (unsigned int) realm->cached_context->num_snaps);
  		return 0;
  	}
  
  	/* alloc new snap context */
  	err = -ENOMEM;
  	if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
  		goto fail;
  	snapc = ceph_create_snap_context(num, GFP_NOFS);
  	if (!snapc)
  		goto fail;
  
  	/* build (reverse sorted) snap vector */
  	num = 0;
  	snapc->seq = realm->seq;
  	if (parent) {
  		u32 i;
  
  		/* include any of parent's snaps occurring _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 (%u snaps)
  ",
  	     realm->ino, realm, snapc, snapc->seq,
  	     (unsigned int) 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
  ", 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
  ", 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, u32 num)
  {
  	u32 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, dirty;
  
  	capsnap = kzalloc(sizeof(*capsnap), GFP_NOFS);
  	if (!capsnap) {
  		pr_err("ENOMEM allocating ceph_cap_snap on %p
  ", inode);
  		return;
  	}
  
  	spin_lock(&ci->i_ceph_lock);
  	used = __ceph_caps_used(ci);
  	dirty = __ceph_caps_dirty(ci);
  
  	/*
  	 * If there is a write in progress, treat that as a dirty Fw,
  	 * even though it hasn't completed yet; by the time we finish
  	 * up this capsnap it will be.
  	 */
  	if (used & CEPH_CAP_FILE_WR)
  		dirty |= CEPH_CAP_FILE_WR;
  
  	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
  ", inode);
  		kfree(capsnap);
  	} else if (dirty & (CEPH_CAP_AUTH_EXCL|CEPH_CAP_XATTR_EXCL|
  			    CEPH_CAP_FILE_EXCL|CEPH_CAP_FILE_WR)) {
  		struct ceph_snap_context *snapc = ci->i_head_snapc;
  
  		/*
  		 * if we are a sync write, we may need to go to the snaprealm
  		 * to get the current snapc.
  		 */
  		if (!snapc)
  			snapc = ci->i_snap_realm->cached_context;
  
  		dout("queue_cap_snap %p cap_snap %p queuing under %p %s
  ",
  		     inode, capsnap, snapc, ceph_cap_string(dirty));
  		ihold(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;
  		capsnap->issued = __ceph_caps_issued(ci, NULL);
  		capsnap->dirty = dirty;
  
  		capsnap->mode = inode->i_mode;
  		capsnap->uid = inode->i_uid;
  		capsnap->gid = inode->i_gid;
  
  		if (dirty & CEPH_CAP_XATTR_EXCL) {
  			__ceph_build_xattrs_blob(ci);
  			capsnap->xattr_blob =
  				ceph_buffer_get(ci->i_xattrs.blob);
  			capsnap->xattr_version = ci->i_xattrs.version;
  		} else {
  			capsnap->xattr_blob = NULL;
  			capsnap->xattr_version = 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 =
  			ceph_get_snap_context(ci->i_snap_realm->cached_context);
  		dout(" new snapc is %p
  ", ci->i_head_snapc);
  		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
  ", 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
  ", inode);
  		kfree(capsnap);
  	}
  
  	spin_unlock(&ci->i_ceph_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_ceph_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_sb_to_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
  ", 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
  ",
  	     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 */
  }
  
  /*
   * Queue cap_snaps for snap writeback for this realm and its children.
   * Called under snap_rwsem, so realm topology won't change.
   */
  static void queue_realm_cap_snaps(struct ceph_snap_realm *realm)
  {
  	struct ceph_inode_info *ci;
  	struct inode *lastinode = NULL;
  	struct ceph_snap_realm *child;
  
  	dout("queue_realm_cap_snaps %p %llx inodes
  ", realm, realm->ino);
  
  	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);
  
  	list_for_each_entry(child, &realm->children, child_item) {
  		dout("queue_realm_cap_snaps %p %llx queue child %p %llx
  ",
  		     realm, realm->ino, child, child->ino);
  		list_del_init(&child->dirty_item);
  		list_add(&child->dirty_item, &realm->dirty_item);
  	}
  
  	list_del_init(&realm->dirty_item);
  	dout("queue_realm_cap_snaps %p %llx done
  ", realm, realm->ino);
  }
  
  /*
   * 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;
  	LIST_HEAD(dirty_realms);
  
  	dout("update_snap_trace deletion=%d
  ", 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;
  		}
  	}
  
  	/* 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) {
  		dout("update_snap_trace updating %llx %p %lld -> %lld
  ",
  		     realm->ino, realm, realm->seq, le64_to_cpu(ri->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;
  
  		/* queue realm for cap_snap creation */
  		list_add(&realm->dirty_item, &dirty_realms);
  
  		invalidate = 1;
  	} else if (!realm->cached_context) {
  		dout("update_snap_trace %llx %p seq %lld new
  ",
  		     realm->ino, realm, realm->seq);
  		invalidate = 1;
  	} else {
  		dout("update_snap_trace %llx %p seq %lld unchanged
  ",
  		     realm->ino, realm, realm->seq);
  	}
  
  	dout("done with %llx %p, invalidated=%d, %p %p
  ", 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);
  
  	/*
  	 * queue cap snaps _after_ we've built the new snap contexts,
  	 * so that i_head_snapc can be set appropriately.
  	 */
  	while (!list_empty(&dirty_realms)) {
  		realm = list_first_entry(&dirty_realms, struct ceph_snap_realm,
  					 dirty_item);
  		queue_realm_cap_snaps(realm);
  	}
  
  	__cleanup_empty_realms(mdsc);
  	return 0;
  
  bad:
  	err = -EINVAL;
  fail:
  	pr_err("update_snap_trace error %d
  ", 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
  ");
  	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;
  		ihold(inode);
  		spin_unlock(&mdsc->snap_flush_lock);
  		spin_lock(&ci->i_ceph_lock);
  		__ceph_flush_snaps(ci, &session, 0);
  		spin_unlock(&ci->i_ceph_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
  ");
  }
  
  
  /*
   * 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->fsc->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
  ", 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
  ", 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;
  			struct ceph_snap_realm *oldrealm;
  
  			if (!inode)
  				continue;
  			ci = ceph_inode(inode);
  
  			spin_lock(&ci->i_ceph_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
  ",
  				     inode, ci->i_snap_realm->ino,
  				     ci->i_snap_realm);
  				goto skip_inode;
  			}
  			dout(" will move %p to split realm %llx %p
  ",
  			     inode, realm->ino, realm);
  			/*
  			 * Move the inode to the new realm
  			 */
  			spin_lock(&realm->inodes_with_caps_lock);
  			list_del_init(&ci->i_snap_realm_item);
  			list_add(&ci->i_snap_realm_item,
  				 &realm->inodes_with_caps);
  			oldrealm = ci->i_snap_realm;
  			ci->i_snap_realm = realm;
  			spin_unlock(&realm->inodes_with_caps_lock);
  			spin_unlock(&ci->i_ceph_lock);
  
  			ceph_get_snap_realm(mdsc, realm);
  			ceph_put_snap_realm(mdsc, oldrealm);
  
  			iput(inode);
  			continue;
  
  skip_inode:
  			spin_unlock(&ci->i_ceph_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)
  		/* 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
  ", mds);
  	ceph_msg_dump(msg);
  out:
  	if (locked_rwsem)
  		up_write(&mdsc->snap_rwsem);
  	return;
  }