[PATCH 06/20] generic_ci_d_compare(): use shortname_storage

Al Viro
2025-01-10T02:43:05Z

... and check the "name might be unstable" predicate
the right way.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/libfs.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 748ac5923154..3ad1b1b7fed6 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1789,7 +1789,7 @@ int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
{
const struct dentry *parent;
const struct inode *dir;
- char strbuf[DNAME_INLINE_LEN];
+ union shortname_store strbuf;
struct qstr qstr;

/*
@@ -1809,22 +1809,23 @@ int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
if (!dir || !IS_CASEFOLDED(dir))
return 1;

+ qstr.len = len;
+ qstr.name = str;
/*
* If the dentry name is stored in-line, then it may be concurrently
* modified by a rename. If this happens, the VFS will eventually retry
* the lookup, so it doesn't matter what ->d_compare() returns.
* However, it's unsafe to call utf8_strncasecmp() with an unstable
* string. Therefore, we have to copy the name into a temporary buffer.
+ * As above, len is guaranteed to match str, so the shortname case
+ * is exactly when str points to ->d_shortname.
*/
- if (len <= DNAME_INLINE_LEN - 1) {
- memcpy(strbuf, str, len);
- strbuf[len] = 0;
- str = strbuf;
+ if (qstr.name == dentry->d_shortname.string) {
+ strbuf = dentry->d_shortname; // NUL is guaranteed to be in there
+ qstr.name = strbuf.string;
/* prevent compiler from optimizing out the temporary buffer */
barrier();
}
- qstr.len = len;
- qstr.name = str;

return utf8_strncasecmp(dentry->d_sb->s_encoding, name, &qstr);
}
--
2.39.5