ceph: using hash value to compose dentry offset

If MDS sorts dentries in dirfrag in hash order, we use hash value to
compose dentry offset. dentry offset is:

  (0xff << 52) | ((24 bits hash) << 28) |
  (the nth entry hash hash collision)

This offset is stable across directory fragmentation. This alos means
there is no need to reset readdir offset if directory get fragmented
in the middle of readdir.

Signed-off-by: Yan, Zheng <zyan@redhat.com>

1 files changed, 25 insertions, 6 deletions

diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index b53c95903aeb..f51b6fd5f570 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -1387,6 +1387,7 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 			     struct ceph_mds_session *session)
 {
 	struct dentry *parent = req->r_dentry;
+	struct ceph_inode_info *ci = ceph_inode(d_inode(parent));
 	struct ceph_mds_reply_info_parsed *rinfo = &req->r_reply_info;
 	struct qstr dname;
 	struct dentry *dn;
@@ -1394,19 +1395,27 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 	int err = 0, skipped = 0, ret, i;
 	struct inode *snapdir = NULL;
 	struct ceph_mds_request_head *rhead = req->r_request->front.iov_base;
-	struct ceph_dentry_info *di;
 	u32 frag = le32_to_cpu(rhead->args.readdir.frag);
+	u32 last_hash = 0;
+	u32 fpos_offset;
 	struct ceph_readdir_cache_control cache_ctl = {};
 
 	if (req->r_aborted)
 		return readdir_prepopulate_inodes_only(req, session);
 
+	if (rinfo->hash_order && req->r_path2) {
+		last_hash = ceph_str_hash(ci->i_dir_layout.dl_dir_hash,
+					  req->r_path2, strlen(req->r_path2));
+		last_hash = ceph_frag_value(last_hash);
+	}
+
 	if (rinfo->dir_dir &&
 	    le32_to_cpu(rinfo->dir_dir->frag) != frag) {
 		dout("readdir_prepopulate got new frag %x -> %x\n",
 		     frag, le32_to_cpu(rinfo->dir_dir->frag));
 		frag = le32_to_cpu(rinfo->dir_dir->frag);
-		req->r_readdir_offset = 2;
+		if (!rinfo->hash_order)
+			req->r_readdir_offset = 2;
 	}
 
 	if (le32_to_cpu(rinfo->head->op) == CEPH_MDS_OP_LSSNAP) {
@@ -1424,13 +1433,13 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 	if (ceph_frag_is_leftmost(frag) && req->r_readdir_offset == 2) {
 		/* note dir version at start of readdir so we can tell
 		 * if any dentries get dropped */
-		struct ceph_inode_info *ci = ceph_inode(d_inode(parent));
 		req->r_dir_release_cnt = atomic64_read(&ci->i_release_count);
 		req->r_dir_ordered_cnt = atomic64_read(&ci->i_ordered_count);
 		req->r_readdir_cache_idx = 0;
 	}
 
 	cache_ctl.index = req->r_readdir_cache_idx;
+	fpos_offset = req->r_readdir_offset;
 
 	/* FIXME: release caps/leases if error occurs */
 	for (i = 0; i < rinfo->dir_nr; i++) {
@@ -1444,6 +1453,18 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 		vino.ino = le64_to_cpu(rde->inode.in->ino);
 		vino.snap = le64_to_cpu(rde->inode.in->snapid);
 
+		if (rinfo->hash_order) {
+			u32 hash = ceph_str_hash(ci->i_dir_layout.dl_dir_hash,
+						 rde->name, rde->name_len);
+			hash = ceph_frag_value(hash);
+			if (hash != last_hash)
+				fpos_offset = 2;
+			last_hash = hash;
+			rde->offset = ceph_make_fpos(hash, fpos_offset++, true);
+		} else {
+			rde->offset = ceph_make_fpos(frag, fpos_offset++, false);
+		}
+
 retry_lookup:
 		dn = d_lookup(parent, &dname);
 		dout("d_lookup on parent=%p name=%.*s got %p\n",
@@ -1521,9 +1542,7 @@ retry_lookup:
 			dn = realdn;
 		}
 
-		di = dn->d_fsdata;
-		di->offset = ceph_make_fpos(frag, i + req->r_readdir_offset);
-		rde->offset = di->offset;
+		ceph_dentry(dn)->offset = rde->offset;
 
 		update_dentry_lease(dn, rde->lease, req->r_session,
 				    req->r_request_started);