for_each_alias(): helper macro for iterating through dentries of given inode

Most of the places using d_alias are loops iterating through all aliases for
given inode; introduce a helper macro (for_each_alias(dentry, inode))
and convert open-coded instances of such loop to it.

They are easier to read that way and it reduces the noise on the next steps.

You _must_ hold inode->i_lock over that thing.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Documentation/filesystems/porting.rst

@@ -1361,3 +1361,13 @@ to match what strlen() would return if it was ran on the string.
 
 However, if the string is freely accessible for the duration of inode's
 lifetime, consider using inode_set_cached_link() instead.
+
+---
+
+**recommended**
+
+If you really need to iterate through dentries for given inode, use
+for_each_alias(dentry, inode) instead of hlist_for_each_entry; better
+yet, see if any of the exported primitives could be used instead of
+the entire loop.  You still need to hold ->i_lock of the inode over
+either form of manual loop.

fs/affs/amigaffs.c

@@ -126,7 +126,7 @@ affs_fix_dcache(struct inode *inode, u32 entry_ino)
 {
 	struct dentry *dentry;
 	spin_lock(&inode->i_lock);
-	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(dentry, inode) {
 		if (entry_ino == (u32)(long)dentry->d_fsdata) {
 			dentry->d_fsdata = (void *)inode->i_ino;
 			break;

fs/ceph/mds_client.c

@@ -4614,7 +4614,7 @@ static struct dentry* d_find_primary(struct inode *inode)
 		goto out_unlock;
 	}
 
-	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(alias, inode) {
 		spin_lock(&alias->d_lock);
 		if (!d_unhashed(alias) &&
 		    (ceph_dentry(alias)->flags & CEPH_DENTRY_PRIMARY_LINK)) {

fs/dcache.c

@@ -790,7 +790,7 @@ void d_mark_dontcache(struct inode *inode)
 	struct dentry *de;
 
 	spin_lock(&inode->i_lock);
-	hlist_for_each_entry(de, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(de, inode) {
 		spin_lock(&de->d_lock);
 		de->d_flags |= DCACHE_DONTCACHE;
 		spin_unlock(&de->d_lock);
@@ -1040,7 +1040,7 @@ static struct dentry *__d_find_alias(struct inode *inode)
 	if (S_ISDIR(inode->i_mode))
 		return __d_find_any_alias(inode);
 
-	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(alias, inode) {
 		spin_lock(&alias->d_lock);
  		if (!d_unhashed(alias)) {
 			dget_dlock(alias);
@@ -1133,7 +1133,7 @@ void d_prune_aliases(struct inode *inode)
 	struct dentry *dentry;
 
 	spin_lock(&inode->i_lock);
-	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias)
+	for_each_alias(dentry, inode)
 		d_dispose_if_unused(dentry, &dispose);
 	spin_unlock(&inode->i_lock);
 	shrink_dentry_list(&dispose);

fs/exportfs/expfs.c

@@ -52,7 +52,7 @@ find_acceptable_alias(struct dentry *result,
 
 	inode = result->d_inode;
 	spin_lock(&inode->i_lock);
-	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(dentry, inode) {
 		dget(dentry);
 		spin_unlock(&inode->i_lock);
 		if (toput)

fs/nfs/dir.c

@@ -1471,7 +1471,7 @@ static void nfs_clear_verifier_file(struct inode *inode)
 	struct dentry *alias;
 	struct inode *dir;
 
-	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(alias, inode) {
 		spin_lock(&alias->d_lock);
 		dir = d_inode_rcu(alias->d_parent);
 		if (!dir ||

fs/notify/fsnotify.c

@@ -76,7 +76,7 @@ void fsnotify_set_children_dentry_flags(struct inode *inode)
 	spin_lock(&inode->i_lock);
 	/* run all of the dentries associated with this inode.  Since this is a
 	 * directory, there damn well better only be one item on this list */
-	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(alias, inode) {
 		struct dentry *child;
 
 		/* run all of the children of the original inode and fix their

fs/ocfs2/dcache.c

@@ -145,7 +145,7 @@ struct dentry *ocfs2_find_local_alias(struct inode *inode,
 	struct dentry *dentry;
 
 	spin_lock(&inode->i_lock);
-	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(dentry, inode) {
 		spin_lock(&dentry->d_lock);
 		if (ocfs2_match_dentry(dentry, parent_blkno, skip_unhashed)) {
 			trace_ocfs2_find_local_alias(dentry->d_name.len,

fs/overlayfs/dir.c

@@ -904,7 +904,7 @@ static void ovl_drop_nlink(struct dentry *dentry)
 
 	/* Try to find another, hashed alias */
 	spin_lock(&inode->i_lock);
-	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(alias, inode) {
 		if (alias != dentry && !d_unhashed(alias))
 			break;
 	}

fs/smb/client/inode.c

@@ -1595,7 +1595,7 @@ inode_has_hashed_dentries(struct inode *inode)
 	struct dentry *dentry;
 
 	spin_lock(&inode->i_lock);
-	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
+	for_each_alias(dentry, inode) {
 		if (!d_unhashed(dentry) || IS_ROOT(dentry)) {
 			spin_unlock(&inode->i_lock);
 			return true;

include/linux/dcache.h

@@ -615,4 +615,8 @@ void set_default_d_op(struct super_block *, const struct dentry_operations *);
 struct dentry *d_make_persistent(struct dentry *, struct inode *);
 void d_make_discardable(struct dentry *dentry);
 
+/* inode->i_lock must be held over that */
+#define for_each_alias(dentry, inode) \
+	hlist_for_each_entry(dentry, &(inode)->i_dentry, d_u.d_alias)
+
 #endif	/* __LINUX_DCACHE_H */