[lustre-devel] [PATCH 16/49] lustre: lmv: striped directory as subdirectory mount

[James Simmons]

From: Lai Siyao <lai.siyao at whamcloud.com>

lmv_intent_lookup() will replace fid1 with stripe FID, but if striped
directory is mounted as subdirectory mount, it should be handled
differently. Because fid2 is directory master object, if stripe is
located on different MDT as master object, it will be treated as
remote object by server, thus server won't reply LOOKUP lock back,
therefore each file access needs to lookup "/".

And remote directory (either plain or striped) shouldn't be used for
subdirectory mount, because remote object can't get LOOKUP lock.
Add an option "mdt_enable_remote_subdir_mount" (1 by default for
backward compatibility), mdt_get_root() will return -EREMOTE if
user specified subdir is a remote directory and this option is
disabled.

WC-bug-id: https://jira.whamcloud.com/browse/LU-14490
Lustre-commit: 775f88ed6c8b623 ("LU-14490 lmv: striped directory as subdirectory mount")
Signed-off-by: Lai Siyao <lai.siyao at whamcloud.com>
Reviewed-on: https://review.whamcloud.com/41893
Reviewed-by: Andreas Dilger <adilger at whamcloud.com>
Reviewed-by: Yingjin Qian <qian at ddn.com>
Reviewed-by: Oleg Drokin <green at whamcloud.com>
Signed-off-by: James Simmons <jsimmons at infradead.org>
---
 fs/lustre/lmv/lmv_intent.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/lustre/lmv/lmv_intent.c b/fs/lustre/lmv/lmv_intent.c
index 38b8c75..2a15ec2 100644
--- a/fs/lustre/lmv/lmv_intent.c
+++ b/fs/lustre/lmv/lmv_intent.c
@@ -451,11 +451,20 @@ static int lmv_intent_lookup(struct obd_export *exp,
 
 retry:
 	if (op_data->op_flags & MF_GETATTR_BY_FID) {
-		/* getattr by FID, replace fid1 with stripe FID */
+		/* getattr by FID, replace fid1 with stripe FID,
+		 * NB, don't replace if name is "/", because it may be a subtree
+		 * mount, and if it's a striped directory, fid1 will be replaced
+		 * to stripe FID by hash, while fid2 is master object FID, which
+		 * will be treated as a remote object if the two FIDs are
+		 * located on different MDTs, and LOOKUP lock can't be fetched.
+		 */
 		LASSERT(op_data->op_name);
-		tgt = lmv_locate_tgt(lmv, op_data);
-		if (IS_ERR(tgt))
-			return PTR_ERR(tgt);
+		if (op_data->op_namelen != 1 ||
+		    strncmp(op_data->op_name, "/", 1) != 0) {
+			tgt = lmv_locate_tgt(lmv, op_data);
+			if (IS_ERR(tgt))
+				return PTR_ERR(tgt);
+		}
 
 		/* name is used to locate stripe target, clear it here
 		 * to avoid packing name in request, so that MDS knows
-- 
1.8.3.1