ceph: cache layout in parent dir on first sync create

If a create is done, then typically we'll end up writing to the file
soon afterward. We don't want to wait for the reply before doing that
when doing an async create, so that means we need the layout for the
new file before we've gotten the response from the MDS.

All files created in a directory will initially inherit the same layout,
so copy off the requisite info from the first synchronous create in the
directory, and save it in a new i_cached_layout field. Zero out the
layout when we lose Dc caps in the dir.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/file.c

@@ -430,6 +430,23 @@ out:
 	return err;
 }
 
+/* Clone the layout from a synchronous create, if the dir now has Dc caps */
+static void
+cache_file_layout(struct inode *dst, struct inode *src)
+{
+	struct ceph_inode_info *cdst = ceph_inode(dst);
+	struct ceph_inode_info *csrc = ceph_inode(src);
+
+	spin_lock(&cdst->i_ceph_lock);
+	if ((__ceph_caps_issued(cdst, NULL) & CEPH_CAP_DIR_CREATE) &&
+	    !ceph_file_layout_is_valid(&cdst->i_cached_layout)) {
+		memcpy(&cdst->i_cached_layout, &csrc->i_layout,
+			sizeof(cdst->i_cached_layout));
+		rcu_assign_pointer(cdst->i_cached_layout.pool_ns,
+				   ceph_try_get_string(csrc->i_layout.pool_ns));
+	}
+	spin_unlock(&cdst->i_ceph_lock);
+}
 
 /*
  * Do a lookup + open with a single request.  If we get a non-existent
@@ -518,7 +535,10 @@ int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
 	} else {
 		dout("atomic_open finish_open on dn %p\n", dn);
 		if (req->r_op == CEPH_MDS_OP_CREATE && req->r_reply_info.has_create_ino) {
-			ceph_init_inode_acls(d_inode(dentry), &as_ctx);
+			struct inode *newino = d_inode(dentry);
+
+			cache_file_layout(dir, newino);
+			ceph_init_inode_acls(newino, &as_ctx);
 			file->f_mode |= FMODE_CREATED;
 		}
 		err = finish_open(file, dentry, ceph_open);