f2fs: introduce F2FS_FEATURE_LOST_FOUND feature

This patch introduces a new feature, F2FS_FEATURE_LOST_FOUND, which
is set by mkfs. mkfs creates a directory named lost+found, which saves
unreachable files. If fsck finds a file which has no parent, or its
parent is removed by fsck, the file will be placed under lost+found
directory by fsck.

lost+found directory could not be encrypted. As a result, the root
directory cannot be encrypted too. So if LOST_FOUND feature is enabled,
let's avoid to encrypt root directory.

Signed-off-by: Sheng Yong <[e-mail]>
Reviewed-by: Chao Yu <[e-mail]>
Signed-off-by: Jaegeuk Kim <[e-mail]>

fs/f2fs/f2fs.h

···
 #define F2FS_FEATURE_FLEXIBLE_INLINE_XATTR	0x0040
 #define F2FS_FEATURE_QUOTA_INO		0x0080
 #define F2FS_FEATURE_INODE_CRTIME	0x0100
+#define F2FS_FEATURE_LOST_FOUND		0x0200
 
 #define F2FS_HAS_FEATURE(sb, mask)					\
 	((F2FS_SB(sb)->raw_super->feature & cpu_to_le32(mask)) != 0)
···
 F2FS_FEATURE_FUNCS(flexible_inline_xattr, FLEXIBLE_INLINE_XATTR);
 F2FS_FEATURE_FUNCS(quota_ino, QUOTA_INO);
 F2FS_FEATURE_FUNCS(inode_crtime, INODE_CRTIME);
+F2FS_FEATURE_FUNCS(lost_found, LOST_FOUND);
 
 #ifdef CONFIG_BLK_DEV_ZONED
 static inline int get_blkz_type(struct f2fs_sb_info *sbi,

fs/f2fs/super.c

···
 static int f2fs_set_context(struct inode *inode, const void *ctx, size_t len,
 							void *fs_data)
 {
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+
+	/*
+	 * Encrypting the root directory is not allowed because fsck
+	 * expects lost+found directory to exist and remain unencrypted
+	 * if LOST_FOUND feature is enabled.
+	 *
+	 */
+	if (f2fs_sb_has_lost_found(sbi->sb) &&
+			inode->i_ino == F2FS_ROOT_INO(sbi))
+		return -EPERM;
+
 	return f2fs_setxattr(inode, F2FS_XATTR_INDEX_ENCRYPTION,
 				F2FS_XATTR_NAME_ENCRYPTION_CONTEXT,
 				ctx, len, fs_data, XATTR_CREATE);

fs/f2fs/sysfs.c

···
 	if (f2fs_sb_has_inode_crtime(sb))
 		len += snprintf(buf + len, PAGE_SIZE - len, "%s%s",
 				len ? ", " : "", "inode_crtime");
+	if (f2fs_sb_has_lost_found(sb))
+		len += snprintf(buf + len, PAGE_SIZE - len, "%s%s",
+				len ? ", " : "", "lost_found");
 	len += snprintf(buf + len, PAGE_SIZE - len, "\n");
 	return len;
 }
···
 	FEAT_FLEXIBLE_INLINE_XATTR,
 	FEAT_QUOTA_INO,
 	FEAT_INODE_CRTIME,
+	FEAT_LOST_FOUND,
 };
 
 static ssize_t f2fs_feature_show(struct f2fs_attr *a,
···
 	case FEAT_FLEXIBLE_INLINE_XATTR:
 	case FEAT_QUOTA_INO:
 	case FEAT_INODE_CRTIME:
+	case FEAT_LOST_FOUND:
 		return snprintf(buf, PAGE_SIZE, "supported\n");
 	}
 	return 0;
···
 F2FS_FEATURE_RO_ATTR(flexible_inline_xattr, FEAT_FLEXIBLE_INLINE_XATTR);
 F2FS_FEATURE_RO_ATTR(quota_ino, FEAT_QUOTA_INO);
 F2FS_FEATURE_RO_ATTR(inode_crtime, FEAT_INODE_CRTIME);
+F2FS_FEATURE_RO_ATTR(lost_found, FEAT_LOST_FOUND);
 
 #define ATTR_LIST(name) (&f2fs_attr_##name.attr)
 static struct attribute *f2fs_attrs[] = {
···
 	ATTR_LIST(flexible_inline_xattr),
 	ATTR_LIST(quota_ino),
 	ATTR_LIST(inode_crtime),
+	ATTR_LIST(lost_found),
 	NULL,
 };