ceph: handle frag mismatch between readdir request and reply

If client has outdated directory fragments information, it may request
readdir an non-existent directory fragment. In this case, the MDS finds
an approximate directory fragment and sends its contents back to the
client. When receiving a reply with fragment that is different than the
requested one, the client need to reset the 'readdir offset'.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>

fs/ceph/dir.c

@@ -352,8 +352,18 @@ more:
 		}
 
 		/* note next offset and last dentry name */
+		rinfo = &req->r_reply_info;
+		if (le32_to_cpu(rinfo->dir_dir->frag) != frag) {
+			frag = le32_to_cpu(rinfo->dir_dir->frag);
+			if (ceph_frag_is_leftmost(frag))
+				fi->next_offset = 2;
+			else
+				fi->next_offset = 0;
+			off = fi->next_offset;
+		}
 		fi->offset = fi->next_offset;
 		fi->last_readdir = req;
+		fi->frag = frag;
 
 		if (req->r_reply_info.dir_end) {
 			kfree(fi->last_name);
@@ -363,7 +373,6 @@ more:
 			else
 				fi->next_offset = 0;
 		} else {
-			rinfo = &req->r_reply_info;
 			err = note_last_dentry(fi,
 				       rinfo->dir_dname[rinfo->dir_nr-1],
 				       rinfo->dir_dname_len[rinfo->dir_nr-1]);

fs/ceph/inode.c

@@ -1275,8 +1275,20 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
 	int err = 0, i;
 	struct inode *snapdir = NULL;
 	struct ceph_mds_request_head *rhead = req->r_request->front.iov_base;
-	u64 frag = le32_to_cpu(rhead->args.readdir.frag);
 	struct ceph_dentry_info *di;
+	u64 r_readdir_offset = req->r_readdir_offset;
+	u32 frag = le32_to_cpu(rhead->args.readdir.frag);
+
+	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);
+		if (ceph_frag_is_leftmost(frag))
+			r_readdir_offset = 2;
+		else
+			r_readdir_offset = 0;
+	}
 
 	if (req->r_aborted)
 		return readdir_prepopulate_inodes_only(req, session);
@@ -1340,7 +1352,7 @@ retry_lookup:
 		}
 
 		di = dn->d_fsdata;
-		di->offset = ceph_make_fpos(frag, i + req->r_readdir_offset);
+		di->offset = ceph_make_fpos(frag, i + r_readdir_offset);
 
 		/* inode */
 		if (dn->d_inode) {

fs/ceph/mds_client.c

@@ -2238,8 +2238,7 @@ static void handle_reply(struct ceph_mds_session *session, struct ceph_msg *msg)
 	err = ceph_fill_trace(mdsc->fsc->sb, req, req->r_session);
 	if (err == 0) {
 		if (result == 0 && (req->r_op == CEPH_MDS_OP_READDIR ||
-				    req->r_op == CEPH_MDS_OP_LSSNAP) &&
-		    rinfo->dir_nr)
+				    req->r_op == CEPH_MDS_OP_LSSNAP))
 			ceph_readdir_prepopulate(req, req->r_session);
 		ceph_unreserve_caps(mdsc, &req->r_caps_reservation);
 	}