ceph: only let auth caps update max_size

Only the auth MDS has a meaningful max_size value for us, so only update it
in fill_inode if we're being issued an auth cap.  Otherwise, a random
stat result from a non-auth MDS can clobber a meaningful max_size, get
the client<->mds cap state out of sync, and make writes hang.

Specifically, even if the client re-requests a larger max_size (which it
will), the MDS won't respond because as far as it knows we already have a
sufficiently large value.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/inode.c

@@ -606,7 +606,14 @@ static int fill_inode(struct inode *inode,
 			    le32_to_cpu(info->time_warp_seq),
 			    &ctime, &mtime, &atime);
 
-	ci->i_max_size = le64_to_cpu(info->max_size);
+	/* only update max_size on auth cap */
+	if ((info->cap.flags & CEPH_CAP_FLAG_AUTH) &&
+	    ci->i_max_size != le64_to_cpu(info->max_size)) {
+		dout("max_size %lld -> %llu\n", ci->i_max_size,
+		     le64_to_cpu(info->max_size));
+		ci->i_max_size = le64_to_cpu(info->max_size);
+	}
+
 	ci->i_layout = info->layout;
 	inode->i_blkbits = fls(le32_to_cpu(info->layout.fl_stripe_unit)) - 1;