fs: add generic xattr_acl handlers

With the ->set_acl inode operation we can implement the Posix ACL
xattr handlers in generic code instead of duplicating them all
over the tree.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

fs/posix_acl.c

···
 #include <linux/sched.h>
 #include <linux/posix_acl.h>
 #include <linux/posix_acl_xattr.h>
+#include <linux/xattr.h>
 #include <linux/export.h>
 #include <linux/user_namespace.h>
 
···
 	return real_size;
 }
 EXPORT_SYMBOL (posix_acl_to_xattr);
+
+static int
+posix_acl_xattr_get(struct dentry *dentry, const char *name,
+		void *value, size_t size, int type)
+{
+	struct posix_acl *acl;
+	int error;
+
+	if (!IS_POSIXACL(dentry->d_inode))
+		return -EOPNOTSUPP;
+	if (S_ISLNK(dentry->d_inode->i_mode))
+		return -EOPNOTSUPP;
+
+	acl = get_acl(dentry->d_inode, type);
+	if (IS_ERR(acl))
+		return PTR_ERR(acl);
+	if (acl == NULL)
+		return -ENODATA;
+
+	error = posix_acl_to_xattr(&init_user_ns, acl, value, size);
+	posix_acl_release(acl);
+
+	return error;
+}
+
+static int
+posix_acl_xattr_set(struct dentry *dentry, const char *name,
+		const void *value, size_t size, int flags, int type)
+{
+	struct inode *inode = dentry->d_inode;
+	struct posix_acl *acl = NULL;
+	int ret;
+
+	if (!IS_POSIXACL(inode))
+		return -EOPNOTSUPP;
+	if (!inode->i_op->set_acl)
+		return -EOPNOTSUPP;
+
+	if (type == ACL_TYPE_DEFAULT && !S_ISDIR(inode->i_mode))
+		return value ? -EACCES : 0;
+	if (!inode_owner_or_capable(inode))
+		return -EPERM;
+
+	if (value) {
+		acl = posix_acl_from_xattr(&init_user_ns, value, size);
+		if (IS_ERR(acl))
+			return PTR_ERR(acl);
+
+		if (acl) {
+			ret = posix_acl_valid(acl);
+			if (ret)
+				goto out;
+		}
+	}
+
+	ret = inode->i_op->set_acl(inode, acl, type);
+out:
+	posix_acl_release(acl);
+	return ret;
+}
+
+static size_t
+posix_acl_xattr_list(struct dentry *dentry, char *list, size_t list_size,
+		const char *name, size_t name_len, int type)
+{
+	const char *xname;
+	size_t size;
+
+	if (!IS_POSIXACL(dentry->d_inode))
+		return -EOPNOTSUPP;
+	if (S_ISLNK(dentry->d_inode->i_mode))
+		return -EOPNOTSUPP;
+
+	if (type == ACL_TYPE_ACCESS)
+		xname = POSIX_ACL_XATTR_ACCESS;
+	else
+		xname = POSIX_ACL_XATTR_DEFAULT;
+
+	size = strlen(xname) + 1;
+	if (list && size <= list_size)
+		memcpy(list, xname, size);
+	return size;
+}
+
+const struct xattr_handler posix_acl_access_xattr_handler = {
+	.prefix = POSIX_ACL_XATTR_ACCESS,
+	.flags = ACL_TYPE_ACCESS,
+	.list = posix_acl_xattr_list,
+	.get = posix_acl_xattr_get,
+	.set = posix_acl_xattr_set,
+};
+EXPORT_SYMBOL_GPL(posix_acl_access_xattr_handler);
+
+const struct xattr_handler posix_acl_default_xattr_handler = {
+	.prefix = POSIX_ACL_XATTR_DEFAULT,
+	.flags = ACL_TYPE_DEFAULT,
+	.list = posix_acl_xattr_list,
+	.get = posix_acl_xattr_get,
+	.set = posix_acl_xattr_set,
+};
+EXPORT_SYMBOL_GPL(posix_acl_default_xattr_handler);

include/linux/posix_acl_xattr.h

···
 int posix_acl_to_xattr(struct user_namespace *user_ns,
 		       const struct posix_acl *acl, void *buffer, size_t size);
 
+extern const struct xattr_handler posix_acl_access_xattr_handler;
+extern const struct xattr_handler posix_acl_default_xattr_handler;
+
 #endif	/* _POSIX_ACL_XATTR_H */