[PATCH] hfsplus: prevent negative dentries when casefolded

[Chung-Chiang Cheng <shepjeng@gmail.com>]

hfsplus uses the case-insensitive filenames by default, but VFS negative
dentries are incompatible with case-insensitive. For example, the
following instructions will get a cached filename 'aaa' which isn't
expected. There is no such problem in macOS.

  touch aaa
  rm aaa
  touch AAA

This patch just takes the same approach as ext4 and f2fs to prevent
negative dentries for this issue.

Signed-off-by: Chung-Chiang Cheng <cccheng@synology.com>
---
 fs/hfsplus/dir.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/hfsplus/dir.c b/fs/hfsplus/dir.c
index 03e6c046faf4..fcab8f09b6af 100644
--- a/fs/hfsplus/dir.c
+++ b/fs/hfsplus/dir.c
@@ -121,6 +121,9 @@ static struct dentry *hfsplus_lookup(struct inode *dir, struct dentry *dentry,
 	if (S_ISREG(inode->i_mode))
 		HFSPLUS_I(inode)->linkid = linkid;
 out:
+	/* Prevent the negative dentry in the casefolded form from being cached */
+	if (!inode && test_bit(HFSPLUS_SB_CASEFOLD, &HFSPLUS_SB(sb)->flags))
+		return NULL;
 	return d_splice_alias(inode, dentry);
 fail:
 	hfs_find_exit(&fd);
@@ -407,6 +410,12 @@ static int hfsplus_unlink(struct inode *dir, struct dentry *dentry)
 		sbi->file_count--;
 	inode->i_ctime = current_time(inode);
 	mark_inode_dirty(inode);
+
+	/* VFS negative dentries are incompatible with encoding and
+	 * case-insensitiveness
+	 */
+	if (test_bit(HFSPLUS_SB_CASEFOLD, &sbi->flags))
+		d_invalidate(dentry);
 out:
 	mutex_unlock(&sbi->vh_mutex);
 	return res;
@@ -429,6 +438,12 @@ static int hfsplus_rmdir(struct inode *dir, struct dentry *dentry)
 	inode->i_ctime = current_time(inode);
 	hfsplus_delete_inode(inode);
 	mark_inode_dirty(inode);
+
+	/* VFS negative dentries are incompatible with encoding and
+	 * case-insensitiveness
+	 */
+	if (test_bit(HFSPLUS_SB_CASEFOLD, &sbi->flags))
+		d_invalidate(dentry);
 out:
 	mutex_unlock(&sbi->vh_mutex);
 	return res;
-- 
2.25.1