staging: erofs: complete POSIX ACL support

Let's add .get_acl() to read the file's acl from its xattrs
to make POSIX ACL usable.

Here is the on-disk detail,
fullname: system.posix_acl_access
struct erofs_xattr_entry:
        .e_name_len = 0
        .e_name_index = EROFS_XATTR_INDEX_POSIX_ACL_ACCESS (2)

fullname: system.posix_acl_default
struct erofs_xattr_entry:
	.e_name_len = 0
	.e_name_index = EROFS_XATTR_INDEX_POSIX_ACL_DEFAULT (3)
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/erofs/Documentation/filesystems/erofs.txt

@@ -36,6 +36,8 @@ Here is the main features of EROFS:
 
  - Support xattr inline and tail-end data inline for all files;
 
+ - Support POSIX.1e ACLs by using xattrs;
+
  - Support transparent file compression as an option:
    LZ4 algorithm with 4 KB fixed-output compression for high performance;
 

drivers/staging/erofs/inode.c

@@ -287,6 +287,7 @@ const struct inode_operations erofs_generic_iops = {
 #ifdef CONFIG_EROFS_FS_XATTR
 	.listxattr = erofs_listxattr,
 #endif
+	.get_acl = erofs_get_acl,
 };
 
 const struct inode_operations erofs_symlink_iops = {
@@ -294,6 +295,7 @@ const struct inode_operations erofs_symlink_iops = {
 #ifdef CONFIG_EROFS_FS_XATTR
 	.listxattr = erofs_listxattr,
 #endif
+	.get_acl = erofs_get_acl,
 };
 
 const struct inode_operations erofs_fast_symlink_iops = {
@@ -301,5 +303,6 @@ const struct inode_operations erofs_fast_symlink_iops = {
 #ifdef CONFIG_EROFS_FS_XATTR
 	.listxattr = erofs_listxattr,
 #endif
+	.get_acl = erofs_get_acl,
 };
 

drivers/staging/erofs/namei.c

@@ -238,5 +238,6 @@ const struct inode_operations erofs_dir_iops = {
 #ifdef CONFIG_EROFS_FS_XATTR
 	.listxattr = erofs_listxattr,
 #endif
+	.get_acl = erofs_get_acl,
 };
 

drivers/staging/erofs/super.c

@@ -398,6 +398,11 @@ static int erofs_read_super(struct super_block *sb,
 	if (!silent)
 		infoln("root inode @ nid %llu", ROOT_NID(sbi));
 
+	if (test_opt(sbi, POSIX_ACL))
+		sb->s_flags |= SB_POSIXACL;
+	else
+		sb->s_flags &= ~SB_POSIXACL;
+
 #ifdef CONFIG_EROFS_FS_ZIP
 	INIT_RADIX_TREE(&sbi->workstn_tree, GFP_ATOMIC);
 #endif
@@ -646,6 +651,11 @@ static int erofs_remount(struct super_block *sb, int *flags, char *data)
 	if (err)
 		goto out;
 
+	if (test_opt(sbi, POSIX_ACL))
+		sb->s_flags |= SB_POSIXACL;
+	else
+		sb->s_flags &= ~SB_POSIXACL;
+
 	*flags |= SB_RDONLY;
 	return 0;
 out:

drivers/staging/erofs/xattr.c

@@ -643,3 +643,40 @@ ssize_t erofs_listxattr(struct dentry *dentry,
 	return shared_listxattr(&it);
 }
 
+#ifdef CONFIG_EROFS_FS_POSIX_ACL
+struct posix_acl *erofs_get_acl(struct inode *inode, int type)
+{
+	struct posix_acl *acl;
+	int prefix, rc;
+	char *value = NULL;
+
+	switch (type) {
+	case ACL_TYPE_ACCESS:
+		prefix = EROFS_XATTR_INDEX_POSIX_ACL_ACCESS;
+		break;
+	case ACL_TYPE_DEFAULT:
+		prefix = EROFS_XATTR_INDEX_POSIX_ACL_DEFAULT;
+		break;
+	default:
+		return ERR_PTR(-EINVAL);
+	}
+
+	rc = erofs_getxattr(inode, prefix, "", NULL, 0);
+	if (rc > 0) {
+		value = kmalloc(rc, GFP_KERNEL);
+		if (!value)
+			return ERR_PTR(-ENOMEM);
+		rc = erofs_getxattr(inode, prefix, "", value, rc);
+	}
+
+	if (rc == -ENOATTR)
+		acl = NULL;
+	else if (rc < 0)
+		acl = ERR_PTR(rc);
+	else
+		acl = posix_acl_from_xattr(&init_user_ns, value, rc);
+	kfree(value);
+	return acl;
+}
+#endif
+

drivers/staging/erofs/xattr.h

@@ -87,5 +87,11 @@ static ssize_t __maybe_unused erofs_listxattr(struct dentry *dentry,
 }
 #endif
 
+#ifdef CONFIG_EROFS_FS_POSIX_ACL
+struct posix_acl *erofs_get_acl(struct inode *inode, int type);
+#else
+#define erofs_get_acl	(NULL)
+#endif
+
 #endif