[PATCH v1 04/54] fs: fat: don't duplicate dentries when resolving differently cased paths

[Ahmad Fatoum]

With case insensitive file systems, like FAT, we should avoid having
multiple dentry cache entries for the same file differing only in
capitalization. Allow case-insensitive file system to set a casefold
flag that barebox will honour when comparing dentries.

That this patch works can be verified using the debug_fs_dump command,
which will show a dentry for each differently cased path in a VFAT,
but only a single dentry once this patch is applied.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 fs/fat/fat.c       | 1 +
 fs/fs.c            | 3 +++
 include/linux/fs.h | 1 +
 3 files changed, 5 insertions(+)

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index cdca666566d2..93d1e08b8456 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -352,6 +352,7 @@ static int fat_probe(struct device *dev)
 		goto err_open;
 
 	priv->cdev = fsdev->cdev;
+	fsdev->sb.s_casefold = true;
 
 	priv->fat.userdata = priv;
 	ret = f_mount(&priv->fat);
diff --git a/fs/fs.c b/fs/fs.c
index cc6f0f7057c3..e997bd5f6a99 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -1562,6 +1562,9 @@ static bool d_same_name(const struct dentry *dentry,
 	if (dentry->d_name.len != name->len)
 		return false;
 
+	if (dentry->d_sb->s_casefold)
+		return strncasecmp(dentry->d_name.name, name->name, name->len) == 0;
+
 	return strncmp(dentry->d_name.name, name->name, name->len) == 0;
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e624b2ce7161..d3813ad9c543 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -160,6 +160,7 @@ struct super_block {
 	unsigned long		s_blocksize;
 	unsigned char		s_blocksize_bits;
 	unsigned char		s_dirt;
+	bool			s_casefold;
 	unsigned long long	s_maxbytes;	/* Max file size */
 	struct file_system_type	*s_type;
 	const struct super_operations	*s_op;
-- 
2.47.3