[PATCH 32/53] ext4: move dcache modifying code out of __ext4_link()

[NeilBrown <neilb@ownmail.net>]

From: NeilBrown <neil@brown.name>

__ext4_link() is separate from ext4_link() so that it can be used for
replaying a "fast_commit" which records a link operation.
Replaying the fast_commit does not require any interaction with the
dcache - it is purely ext4-local - but it uses a dentry to simplify code
reuse.

An interface it uses - d_alloc() - is not generally useful and will soon
be removed.  This patch prepares ext4 for that removal.  Specifically it
removes all dcache-modification code from __ext4_link().  This will mean
that __ext4_link() treats the dentry as read-only so fast_commit reply
can simply provide an on-stack dentry.

Various "const" markers are sprinkled around to confirm that the dentry
is treated read-only.

This patch only rearranges code and slightly re-orders it, so those
changes can be reviewed separately.  The next patch will remove the use
of d_alloc().

Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/dcache.c                 |  2 +-
 fs/ext4/ext4.h              |  4 ++--
 fs/ext4/fast_commit.c       | 14 +++++++++++---
 fs/ext4/namei.c             | 23 +++++++++++++----------
 include/linux/dcache.h      |  2 +-
 include/trace/events/ext4.h |  4 ++--
 6 files changed, 30 insertions(+), 19 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index a1219b446b74..c48337d95f9a 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -358,7 +358,7 @@ static inline int dname_external(const struct dentry *dentry)
 	return dentry->d_name.name != dentry->d_shortname.string;
 }
 
-void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
+void take_dentry_name_snapshot(struct name_snapshot *name, const struct dentry *dentry)
 {
 	unsigned seq;
 	const unsigned char *s;
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 293f698b7042..1794407652ff 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2972,7 +2972,7 @@ void ext4_fc_track_range(handle_t *handle, struct inode *inode, ext4_lblk_t star
 void __ext4_fc_track_unlink(handle_t *handle, struct inode *inode,
 	struct dentry *dentry);
 void __ext4_fc_track_link(handle_t *handle, struct inode *inode,
-	struct dentry *dentry);
+	const struct dentry *dentry);
 void ext4_fc_track_unlink(handle_t *handle, struct dentry *dentry);
 void ext4_fc_track_link(handle_t *handle, struct dentry *dentry);
 void __ext4_fc_track_create(handle_t *handle, struct inode *inode,
@@ -3719,7 +3719,7 @@ extern int ext4_handle_dirty_dirblock(handle_t *handle, struct inode *inode,
 extern int __ext4_unlink(struct inode *dir, const struct qstr *d_name,
 			 struct inode *inode, struct dentry *dentry);
 extern int __ext4_link(struct inode *dir, struct inode *inode,
-		       struct dentry *dentry);
+		       const struct dentry *dentry);
 
 #define S_SHIFT 12
 static const unsigned char ext4_type_by_mode[(S_IFMT >> S_SHIFT) + 1] = {
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index f575751f1cae..2a5daf1d9667 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -388,7 +388,7 @@ static int ext4_fc_track_template(
 }
 
 struct __track_dentry_update_args {
-	struct dentry *dentry;
+	const struct dentry *dentry;
 	int op;
 };
 
@@ -400,7 +400,7 @@ static int __track_dentry_update(handle_t *handle, struct inode *inode,
 	struct ext4_inode_info *ei = EXT4_I(inode);
 	struct __track_dentry_update_args *dentry_update =
 		(struct __track_dentry_update_args *)arg;
-	struct dentry *dentry = dentry_update->dentry;
+	const struct dentry *dentry = dentry_update->dentry;
 	struct inode *dir = dentry->d_parent->d_inode;
 	struct super_block *sb = inode->i_sb;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -483,7 +483,7 @@ void ext4_fc_track_unlink(handle_t *handle, struct dentry *dentry)
 }
 
 void __ext4_fc_track_link(handle_t *handle,
-	struct inode *inode, struct dentry *dentry)
+	struct inode *inode, const struct dentry *dentry)
 {
 	struct __track_dentry_update_args args;
 	int ret;
@@ -1471,7 +1471,15 @@ static int ext4_fc_replay_link_internal(struct super_block *sb,
 		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);
+	}
 	/*
 	 * It's possible that link already existed since data blocks
 	 * for the dir in question got persisted before we crashed OR
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index c4b5e252af0e..80e1051cab44 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2353,7 +2353,7 @@ static int make_indexed_dir(handle_t *handle, struct ext4_filename *fname,
  * may not sleep between calling this and putting something into
  * the entry, as someone else might have used it while you slept.
  */
-static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
+static int ext4_add_entry(handle_t *handle, const struct dentry *dentry,
 			  struct inode *inode)
 {
 	struct inode *dir = d_inode(dentry->d_parent);
@@ -3445,7 +3445,7 @@ static int ext4_symlink(struct mnt_idmap *idmap, struct inode *dir,
 	return err;
 }
 
-int __ext4_link(struct inode *dir, struct inode *inode, struct dentry *dentry)
+int __ext4_link(struct inode *dir, struct inode *inode, const struct dentry *dentry)
 {
 	handle_t *handle;
 	int err, retries = 0;
@@ -3460,8 +3460,6 @@ int __ext4_link(struct inode *dir, struct inode *inode, struct dentry *dentry)
 		ext4_handle_sync(handle);
 
 	inode_set_ctime_current(inode);
-	ext4_inc_count(inode);
-	ihold(inode);
 
 	err = ext4_add_entry(handle, dentry, inode);
 	if (!err) {
@@ -3471,11 +3469,7 @@ int __ext4_link(struct inode *dir, struct inode *inode, struct dentry *dentry)
 		 */
 		if (inode->i_nlink == 1)
 			ext4_orphan_del(handle, inode);
-		d_instantiate(dentry, inode);
-		ext4_fc_track_link(handle, dentry);
-	} else {
-		drop_nlink(inode);
-		iput(inode);
+		__ext4_fc_track_link(handle, inode, dentry);
 	}
 	ext4_journal_stop(handle);
 	if (err == -ENOSPC && ext4_should_retry_alloc(dir->i_sb, &retries))
@@ -3504,7 +3498,16 @@ static int ext4_link(struct dentry *old_dentry,
 	err = dquot_initialize(dir);
 	if (err)
 		return err;
-	return __ext4_link(dir, inode, dentry);
+	ihold(inode);
+	ext4_inc_count(inode);
+	err = __ext4_link(dir, inode, dentry);
+	if (err) {
+		drop_nlink(inode);
+		iput(inode);
+	} else {
+		d_instantiate(dentry, inode);
+	}
+	return err;
 }
 
 /*
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index a97eb151d9db..3b12577ddfbb 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -600,7 +600,7 @@ struct name_snapshot {
 	struct qstr name;
 	union shortname_store inline_name;
 };
-void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
+void take_dentry_name_snapshot(struct name_snapshot *, const struct dentry *);
 void release_dentry_name_snapshot(struct name_snapshot *);
 
 static inline struct dentry *d_first_child(const struct dentry *dentry)
diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
index a3e8fe414df8..efcf1018c208 100644
--- a/include/trace/events/ext4.h
+++ b/include/trace/events/ext4.h
@@ -2870,7 +2870,7 @@ TRACE_EVENT(ext4_fc_stats,
 DECLARE_EVENT_CLASS(ext4_fc_track_dentry,
 
 	TP_PROTO(handle_t *handle, struct inode *inode,
-		 struct dentry *dentry, int ret),
+		 const struct dentry *dentry, int ret),
 
 	TP_ARGS(handle, inode, dentry, ret),
 
@@ -2902,7 +2902,7 @@ DECLARE_EVENT_CLASS(ext4_fc_track_dentry,
 #define DEFINE_EVENT_CLASS_DENTRY(__type)				\
 DEFINE_EVENT(ext4_fc_track_dentry, ext4_fc_track_##__type,		\
 	TP_PROTO(handle_t *handle, struct inode *inode,			\
-		 struct dentry *dentry, int ret),			\
+		 const struct dentry *dentry, int ret),			\
 	TP_ARGS(handle, inode, dentry, ret)				\
 )
 
-- 
2.50.0.107.gf914562f5916.dirty