[PATCH 36/53] cephfs: remove d_alloc from CEPH_MDS_OP_LOOKUPNAME handling in ceph_fill_trace()

[NeilBrown]

From: NeilBrown <neil at brown.name>

When performing a get_name export_operation, ceph sends a LOOKUPNAME op
to the server.  When it gets a reply it tries to look up the name
locally and if the name exists in the dcache with the wrong inode, it
discards the result and tries again.

If it doesn't find the name in the dcache it will allocate a new dentry
and never make any use of it.  The dentry is never instantiated and is
assigned to ->r_dentry which is then freed by post-op cleanup.

As this is a waste, and as there is a plan to remove d_alloc(), this
code is discarded.

Also try_lookup_noperm() is used in place of full_name_hash() and
d_lookup(), and QSTR_LEN() is used to initialise dname.

Signed-off-by: NeilBrown <neil at brown.name>
---
 fs/ceph/inode.c | 29 +++++++----------------------
 1 file changed, 7 insertions(+), 22 deletions(-)

diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 59f9f6948bb2..0982fbda2a82 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -15,6 +15,7 @@
 #include <linux/sort.h>
 #include <linux/iversion.h>
 #include <linux/fscrypt.h>
+#include <linux/namei.h>
 
 #include "super.h"
 #include "mds_client.h"
@@ -1623,33 +1624,17 @@ int ceph_fill_trace(struct super_block *sb, struct ceph_mds_request *req)
 				ceph_fname_free_buffer(parent_dir, &oname);
 				goto done;
 			}
-			dname.name = oname.name;
-			dname.len = oname.len;
-			dname.hash = full_name_hash(parent, dname.name, dname.len);
+			dname = QSTR_LEN(oname.name, oname.len);
 			tvino.ino = le64_to_cpu(rinfo->targeti.in->ino);
 			tvino.snap = le64_to_cpu(rinfo->targeti.in->snapid);
 retry_lookup:
-			dn = d_lookup(parent, &dname);
+			dn = try_lookup_noperm(&dname, parent);
 			doutc(cl, "d_lookup on parent=%p name=%.*s got %p\n",
 			      parent, dname.len, dname.name, dn);
-
-			if (!dn) {
-				dn = d_alloc(parent, &dname);
-				doutc(cl, "d_alloc %p '%.*s' = %p\n", parent,
-				      dname.len, dname.name, dn);
-				if (!dn) {
-					dput(parent);
-					ceph_fname_free_buffer(parent_dir, &oname);
-					err = -ENOMEM;
-					goto done;
-				}
-				if (is_nokey) {
-					spin_lock(&dn->d_lock);
-					dn->d_flags |= DCACHE_NOKEY_NAME;
-					spin_unlock(&dn->d_lock);
-				}
-				err = 0;
-			} else if (d_really_is_positive(dn) &&
+			if (IS_ERR(dn))
+				/* should be impossible */
+				dn = NULL;
+			if (dn && d_really_is_positive(dn) &&
 				   (ceph_ino(d_inode(dn)) != tvino.ino ||
 				    ceph_snap(d_inode(dn)) != tvino.snap)) {
 				doutc(cl, " dn %p points to wrong inode %p\n",
-- 
2.50.0.107.gf914562f5916.dirty