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 <[e-mail]>

fs/ceph/dir.c

···
 }
 
 /*
- * for readdir, we encode the directory frag and offset within that
- * frag into f_pos.
+ * for f_pos for readdir:
+ * - hash order:
+ *	(0xff << 52) | ((24 bits hash) << 28) |
+ *	(the nth entry has hash collision);
+ * - frag+name order;
+ *	((frag value) << 28) | (the nth entry in frag);
  */
+#define OFFSET_BITS	28
+#define OFFSET_MASK	((1 << OFFSET_BITS) - 1)
+#define HASH_ORDER	(0xffull << (OFFSET_BITS + 24))
+loff_t ceph_make_fpos(unsigned high, unsigned off, bool hash_order)
+{
+	loff_t fpos = ((loff_t)high << 28) | (loff_t)off;
+	if (hash_order)
+		fpos |= HASH_ORDER;
+	return fpos;
+}
+
+static bool is_hash_order(loff_t p)
+{
+	return (p & HASH_ORDER) == HASH_ORDER;
+}
+
 static unsigned fpos_frag(loff_t p)
 {
-	return p >> 32;
+	return p >> OFFSET_BITS;
 }
+
+static unsigned fpos_hash(loff_t p)
+{
+	return ceph_frag_value(fpos_frag(p));
+}
+
 static unsigned fpos_off(loff_t p)
 {
-	return p & 0xffffffff;
+	return p & OFFSET_MASK;
 }
 
 static int fpos_cmp(loff_t l, loff_t r)
···
 	u64 idx = 0;
 	int err = 0;
 
-	dout("__dcache_readdir %p v%u at %llu\n", dir, shared_gen, ctx->pos);
+	dout("__dcache_readdir %p v%u at %llx\n", dir, shared_gen, ctx->pos);
 
 	/* search start position */
 	if (ctx->pos > 2) {
···
 		spin_unlock(&dentry->d_lock);
 
 		if (emit_dentry) {
-			dout(" %llu (%llu) dentry %p %pd %p\n", di->offset, ctx->pos,
+			dout(" %llx dentry %p %pd %p\n", di->offset,
 			     dentry, dentry, d_inode(dentry));
 			ctx->pos = di->offset;
 			if (!dir_emit(ctx, dentry->d_name.name,
···
 	return err;
 }
 
+static bool need_send_readdir(struct ceph_file_info *fi, loff_t pos)
+{
+	if (!fi->last_readdir)
+		return true;
+	if (is_hash_order(pos))
+		return !ceph_frag_contains_value(fi->frag, fpos_hash(pos));
+	else
+		return fi->frag != fpos_frag(pos);
+}
+
 static int ceph_readdir(struct file *file, struct dir_context *ctx)
 {
 	struct ceph_file_info *fi = file->private_data;
···
 	struct ceph_inode_info *ci = ceph_inode(inode);
 	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
 	struct ceph_mds_client *mdsc = fsc->mdsc;
-	unsigned frag = fpos_frag(ctx->pos);
 	int i;
 	int err;
 	u32 ftype;
···
 		err = __dcache_readdir(file, ctx, shared_gen);
 		if (err != -EAGAIN)
 			return err;
-		frag = fpos_frag(ctx->pos);
 	} else {
 		spin_unlock(&ci->i_ceph_lock);
 	}
···
 	/* proceed with a normal readdir */
 more:
 	/* do we have the correct frag content buffered? */
-	if (fi->frag != frag || fi->last_readdir == NULL) {
+	if (need_send_readdir(fi, ctx->pos)) {
 		struct ceph_mds_request *req;
+		unsigned frag;
 		int op = ceph_snap(inode) == CEPH_SNAPDIR ?
 			CEPH_MDS_OP_LSSNAP : CEPH_MDS_OP_READDIR;
 
···
 		if (fi->last_readdir) {
 			ceph_mdsc_put_request(fi->last_readdir);
 			fi->last_readdir = NULL;
+		}
+
+		if (is_hash_order(ctx->pos)) {
+			frag = ceph_choose_frag(ci, fpos_hash(ctx->pos),
+						NULL, NULL);
+		} else {
+			frag = fpos_frag(ctx->pos);
 		}
 
 		dout("readdir fetching %llx.%llx frag %x offset '%s'\n",
···
 			ceph_mdsc_put_request(req);
 			return err;
 		}
-		dout("readdir got and parsed readdir result=%d"
-		     " on frag %x, end=%d, complete=%d\n", err, frag,
+		dout("readdir got and parsed readdir result=%d on "
+		     "frag %x, end=%d, complete=%d, hash_order=%d\n",
+		     err, frag,
 		     (int)req->r_reply_info.dir_end,
-		     (int)req->r_reply_info.dir_complete);
+		     (int)req->r_reply_info.dir_complete,
+		     (int)req->r_reply_info.hash_order);
 
-
-		/* 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);
-			fi->next_offset = req->r_readdir_offset;
-			/* adjust ctx->pos to beginning of frag */
-			ctx->pos = ceph_make_fpos(frag, fi->next_offset);
+			if (!rinfo->hash_order) {
+				fi->next_offset = req->r_readdir_offset;
+				/* adjust ctx->pos to beginning of frag */
+				ctx->pos = ceph_make_fpos(frag,
+							  fi->next_offset,
+							  false);
+			}
 		}
 
 		fi->frag = frag;
···
 			fi->dir_release_count = 0;
 		}
 
-		if (req->r_reply_info.dir_end) {
-			kfree(fi->last_name);
-			fi->last_name = NULL;
-			fi->next_offset = 2;
-		} else {
+		/* note next offset and last dentry name */
+		if (rinfo->dir_nr > 0) {
 			struct ceph_mds_reply_dir_entry *rde =
 					rinfo->dir_entries + (rinfo->dir_nr-1);
+			unsigned next_offset = req->r_reply_info.dir_end ?
+					2 : (fpos_off(rde->offset) + 1);
 			err = note_last_dentry(fi, rde->name, rde->name_len,
-					       fpos_off(rde->offset) + 1);
+					       next_offset);
 			if (err)
 				return err;
+		} else if (req->r_reply_info.dir_end) {
+			fi->next_offset = 2;
+			/* keep last name */
 		}
 	}
 
 	rinfo = &fi->last_readdir->r_reply_info;
 	dout("readdir frag %x num %d pos %llx chunk first %llx\n",
-	     frag, rinfo->dir_nr, ctx->pos,
+	     fi->frag, rinfo->dir_nr, ctx->pos,
 	     rinfo->dir_nr ? rinfo->dir_entries[0].offset : 0LL);
 
 	i = 0;
···
 		ctx->pos++;
 	}
 
-	if (fi->last_name) {
+	if (fi->next_offset > 2) {
 		ceph_mdsc_put_request(fi->last_readdir);
 		fi->last_readdir = NULL;
 		goto more;
 	}
 
 	/* more frags? */
-	if (!ceph_frag_is_rightmost(frag)) {
-		frag = ceph_frag_next(frag);
-		ctx->pos = ceph_make_fpos(frag, 2);
+	if (!ceph_frag_is_rightmost(fi->frag)) {
+		unsigned frag = ceph_frag_next(fi->frag);
+		if (is_hash_order(ctx->pos)) {
+			loff_t new_pos = ceph_make_fpos(ceph_frag_value(frag),
+							fi->next_offset, true);
+			if (new_pos > ctx->pos)
+				ctx->pos = new_pos;
+			/* keep last_name */
+		} else {
+			ctx->pos = ceph_make_fpos(frag, fi->next_offset, false);
+			kfree(fi->last_name);
+			fi->last_name = NULL;
+		}
 		dout("readdir next frag is %x\n", frag);
 		goto more;
 	}
···
 static bool need_reset_readdir(struct ceph_file_info *fi, loff_t new_pos)
 {
 	struct ceph_mds_reply_info_parsed *rinfo;
+	loff_t chunk_offset;
 	if (new_pos == 0)
 		return true;
-	if (fpos_frag(new_pos) != fi->frag)
+	if (is_hash_order(new_pos)) {
+		/* no need to reset last_name for a forward seek when
+		 * dentries are sotred in hash order */
+	} else if (fi->frag |= fpos_frag(new_pos)) {
 		return true;
+	}
 	rinfo = fi->last_readdir ? &fi->last_readdir->r_reply_info : NULL;
 	if (!rinfo || !rinfo->dir_nr)
 		return true;
-	return new_pos < rinfo->dir_entries[0].offset;;
+	chunk_offset = rinfo->dir_entries[0].offset;
+	return new_pos < chunk_offset ||
+	       is_hash_order(new_pos) != is_hash_order(chunk_offset);
 }
 
 static loff_t ceph_dir_llseek(struct file *file, loff_t offset, int whence)
···
 	}
 
 	if (offset >= 0) {
+		if (need_reset_readdir(fi, offset)) {
+			dout("dir_llseek dropping %p content\n", file);
+			reset_readdir(fi);
+		} else if (is_hash_order(offset) && offset > file->f_pos) {
+			/* for hash offset, we don't know if a forward seek
+			 * is within same frag */
+			fi->dir_release_count = 0;
+			fi->readdir_cache_idx = -1;
+		}
+
 		if (offset != file->f_pos) {
 			file->f_pos = offset;
 			file->f_version = 0;
 			fi->flags &= ~CEPH_F_ATEND;
 		}
 		retval = offset;
-
-		if (need_reset_readdir(fi, offset)) {
-			dout("dir_llseek dropping %p content\n", file);
-			reset_readdir(fi);
-		}
 	}
 out:
 	inode_unlock(inode);

fs/ceph/inode.c

···
 			     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;
···
 	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) {
···
 	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++) {
···
 
 		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);
···
 			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);

fs/ceph/mds_client.c

···
 		u16 flags = ceph_decode_16(p);
 		info->dir_end = !!(flags & CEPH_READDIR_FRAG_END);
 		info->dir_complete = !!(flags & CEPH_READDIR_FRAG_COMPLETE);
+		info->hash_order = !!(flags & CEPH_READDIR_HASH_ORDER);
 	}
 	if (num == 0)
 		goto done;

fs/ceph/mds_client.h

···
 			struct ceph_mds_reply_dirfrag *dir_dir;
 			size_t			      dir_buf_size;
 			int                           dir_nr;
-			bool			      dir_complete, dir_end;
+			bool			      dir_complete;
+			bool			      dir_end;
+			bool			      hash_order;
 			struct ceph_mds_reply_dir_entry  *dir_entries;
 		};
 

fs/ceph/super.h

···
 	return (struct ceph_dentry_info *)dentry->d_fsdata;
 }
 
-static inline loff_t ceph_make_fpos(unsigned frag, unsigned off)
-{
-	return ((loff_t)frag << 32) | (loff_t)off;
-}
-
 /*
  * caps helpers
  */
···
 extern const struct dentry_operations ceph_dentry_ops, ceph_snap_dentry_ops,
 	ceph_snapdir_dentry_ops;
 
+extern loff_t ceph_make_fpos(unsigned high, unsigned off, bool hash_order);
 extern int ceph_handle_notrace_create(struct inode *dir, struct dentry *dentry);
 extern int ceph_handle_snapdir(struct ceph_mds_request *req,
 			       struct dentry *dentry, int err);

include/linux/ceph/ceph_fs.h

···
  */
 #define CEPH_READDIR_FRAG_END		(1<<0)
 #define CEPH_READDIR_FRAG_COMPLETE	(1<<8)
+#define CEPH_READDIR_HASH_ORDER		(1<<9)
 
 union ceph_mds_request_args {
 	struct {