[PATCH 33/53] ext4: use on-stack dentries in ext4_fc_replay_link_internal()

[NeilBrown <neilb@ownmail.net>]

From: NeilBrown <neil@brown.name>

ext4_fc_replay_link_internal() uses two dentries to simply code-reuse
when replaying a "link" operation.  It does not need to interact with
the dcache and removes the dentries shortly after adding them.

They are passed to __ext4_link() which only performs read accesses on
these dentries and only uses the name and parent of dentry_inode (plus
checking a flag is unset) and only uses the inode of the parent.

So instead of allocating dentries and adding them to the dcache, allocat
two dentries on the stack, set up the required fields, and pass these to
__ext4_link().

This substantially simplifies the code and removes on of the few uses of
d_alloc() - preparing for its removal.

Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/ext4/fast_commit.c | 40 ++++++++--------------------------------
 1 file changed, 8 insertions(+), 32 deletions(-)

diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 2a5daf1d9667..e3593bb90a62 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -1446,8 +1446,6 @@ static int ext4_fc_replay_link_internal(struct super_block *sb,
 				struct inode *inode)
 {
 	struct inode *dir = NULL;
-	struct dentry *dentry_dir = NULL, *dentry_inode = NULL;
-	struct qstr qstr_dname = QSTR_INIT(darg->dname, darg->dname_len);
 	int ret = 0;
 
 	dir = ext4_iget(sb, darg->parent_ino, EXT4_IGET_NORMAL);
@@ -1457,28 +1455,14 @@ static int ext4_fc_replay_link_internal(struct super_block *sb,
 		goto out;
 	}
 
-	dentry_dir = d_obtain_alias(dir);
-	if (IS_ERR(dentry_dir)) {
-		ext4_debug("Failed to obtain dentry");
-		dentry_dir = NULL;
-		goto out;
-	}
+	{
+		struct dentry dentry_dir = { .d_inode = dir };
+		const struct dentry dentry_inode = {
+			.d_parent = &dentry_dir,
+			.d_name = QSTR_LEN(darg->dname, darg->dname_len),
+		};
 
-	dentry_inode = d_alloc(dentry_dir, &qstr_dname);
-	if (!dentry_inode) {
-		ext4_debug("Inode dentry not created.");
-		ret = -ENOMEM;
-		goto out;
-	}
-
-	ihold(inode);
-	inc_nlink(inode);
-	ret = __ext4_link(dir, inode, dentry_inode);
-	if (ret) {
-		drop_nlink(inode);
-		iput(inode);
-	} else {
-		d_instantiate(dentry_inode, inode);
+		ret = __ext4_link(dir, inode, &dentry_inode);
 	}
 	/*
 	 * It's possible that link already existed since data blocks
@@ -1493,16 +1477,8 @@ static int ext4_fc_replay_link_internal(struct super_block *sb,
 
 	ret = 0;
 out:
-	if (dentry_dir) {
-		d_drop(dentry_dir);
-		dput(dentry_dir);
-	} else if (dir) {
+	if (dir)
 		iput(dir);
-	}
-	if (dentry_inode) {
-		d_drop(dentry_inode);
-		dput(dentry_inode);
-	}
 
 	return ret;
 }
-- 
2.50.0.107.gf914562f5916.dirty