Enable setting flag FS_CASEFOLD_FL for tmpfs directories, when tmpfs is
mounted with casefold support. A special check is need for this flag,
since it can't be set for non-empty directories.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
---
Changes from v2:
- Fixed bug when adding a non-casefold flag in a non-empty dir
---
 include/linux/shmem_fs.h |  6 ++---
 mm/shmem.c               | 70 +++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 67 insertions(+), 9 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 515a9a6a3c6f82c55952d821887514217a6a00d1..018da28c01e7d71b8fb00bfb23c000248c8a83f4 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -42,10 +42,10 @@ struct shmem_inode_info {
 	struct inode		vfs_inode;
 };
 
-#define SHMEM_FL_USER_VISIBLE		FS_FL_USER_VISIBLE
+#define SHMEM_FL_USER_VISIBLE		(FS_FL_USER_VISIBLE | FS_CASEFOLD_FL)
 #define SHMEM_FL_USER_MODIFIABLE \
-	(FS_IMMUTABLE_FL | FS_APPEND_FL | FS_NODUMP_FL | FS_NOATIME_FL)
-#define SHMEM_FL_INHERITED		(FS_NODUMP_FL | FS_NOATIME_FL)
+	(FS_IMMUTABLE_FL | FS_APPEND_FL | FS_NODUMP_FL | FS_NOATIME_FL | FS_CASEFOLD_FL)
+#define SHMEM_FL_INHERITED		(FS_NODUMP_FL | FS_NOATIME_FL | FS_CASEFOLD_FL)
 
 struct shmem_quota_limits {
 	qsize_t usrquota_bhardlimit; /* Default user quota block hard limit */
diff --git a/mm/shmem.c b/mm/shmem.c
index 935e824990799d927098fd88ebaba384a6284f42..1c130a7d58ff3a4f5f920374414f9e7a29347ed9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2760,13 +2760,62 @@ static int shmem_file_open(struct inode *inode, struct file *file)
 #ifdef CONFIG_TMPFS_XATTR
 static int shmem_initxattrs(struct inode *, const struct xattr *, void *);
 
+#if IS_ENABLED(CONFIG_UNICODE)
+/*
+ * shmem_inode_casefold_flags - Deal with casefold file attribute flag
+ *
+ * The casefold file attribute needs some special checks. I can just be added to
+ * an empty dir, and can't be removed from a non-empty dir.
+ */
+static int shmem_inode_casefold_flags(struct inode *inode, unsigned int fsflags,
+				      struct dentry *dentry, unsigned int *i_flags)
+{
+	unsigned int old = inode->i_flags;
+	struct super_block *sb = inode->i_sb;
+
+	if (fsflags & FS_CASEFOLD_FL) {
+		if (!(old & S_CASEFOLD)) {
+			if (!sb->s_encoding)
+				return -EOPNOTSUPP;
+
+			if (!S_ISDIR(inode->i_mode))
+				return -ENOTDIR;
+
+			if (dentry && !simple_empty(dentry))
+				return -ENOTEMPTY;
+		}
+
+		*i_flags = *i_flags | S_CASEFOLD;
+	} else if (old & S_CASEFOLD) {
+		if (dentry && !simple_empty(dentry))
+			return -ENOTEMPTY;
+	}
+
+	return 0;
+}
+#else
+static int shmem_inode_casefold_flags(struct inode *inode, unsigned int fsflags,
+				      struct dentry *dentry, unsigned int *i_flags)
+{
+	if (fsflags & FS_CASEFOLD_FL)
+		return -EOPNOTSUPP;
+
+	return 0;
+}
+#endif
+
 /*
  * chattr's fsflags are unrelated to extended attributes,
  * but tmpfs has chosen to enable them under the same config option.
  */
-static void shmem_set_inode_flags(struct inode *inode, unsigned int fsflags)
+static int shmem_set_inode_flags(struct inode *inode, unsigned int fsflags, struct dentry *dentry)
 {
 	unsigned int i_flags = 0;
+	int ret;
+
+	ret = shmem_inode_casefold_flags(inode, fsflags, dentry, &i_flags);
+	if (ret)
+		return ret;
 
 	if (fsflags & FS_NOATIME_FL)
 		i_flags |= S_NOATIME;
@@ -2777,10 +2826,12 @@ static void shmem_set_inode_flags(struct inode *inode, unsigned int fsflags)
 	/*
 	 * But FS_NODUMP_FL does not require any action in i_flags.
 	 */
-	inode_set_flags(inode, i_flags, S_NOATIME | S_APPEND | S_IMMUTABLE);
+	inode_set_flags(inode, i_flags, S_NOATIME | S_APPEND | S_IMMUTABLE | S_CASEFOLD);
+
+	return 0;
 }
 #else
-static void shmem_set_inode_flags(struct inode *inode, unsigned int fsflags)
+static void shmem_set_inode_flags(struct inode *inode, unsigned int fsflags, struct dentry *dentry)
 {
 }
 #define shmem_initxattrs NULL
@@ -2827,7 +2878,7 @@ static struct inode *__shmem_get_inode(struct mnt_idmap *idmap,
 	info->fsflags = (dir == NULL) ? 0 :
 		SHMEM_I(dir)->fsflags & SHMEM_FL_INHERITED;
 	if (info->fsflags)
-		shmem_set_inode_flags(inode, info->fsflags);
+		shmem_set_inode_flags(inode, info->fsflags, NULL);
 	INIT_LIST_HEAD(&info->shrinklist);
 	INIT_LIST_HEAD(&info->swaplist);
 	simple_xattrs_init(&info->xattrs);
@@ -3934,16 +3985,23 @@ static int shmem_fileattr_set(struct mnt_idmap *idmap,
 {
 	struct inode *inode = d_inode(dentry);
 	struct shmem_inode_info *info = SHMEM_I(inode);
+	int ret, flags;
 
 	if (fileattr_has_fsx(fa))
 		return -EOPNOTSUPP;
 	if (fa->flags & ~SHMEM_FL_USER_MODIFIABLE)
 		return -EOPNOTSUPP;
 
-	info->fsflags = (info->fsflags & ~SHMEM_FL_USER_MODIFIABLE) |
+	flags = (info->fsflags & ~SHMEM_FL_USER_MODIFIABLE) |
 		(fa->flags & SHMEM_FL_USER_MODIFIABLE);
 
-	shmem_set_inode_flags(inode, info->fsflags);
+	ret = shmem_set_inode_flags(inode, flags, dentry);
+
+	if (ret)
+		return ret;
+
+	info->fsflags = flags;
+
 	inode_set_ctime_current(inode);
 	inode_inc_iversion(inode);
 	return 0;

-- 
2.47.0