exportfs: add permission method

This allows filesystems such as pidfs to provide their custom permission
checks.

Link: https://lore.kernel.org/r/20241129-work-pidfs-file_handle-v1-5-87d803a42495@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 16 insertions, 1 deletions

diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index c69b79b64466..a087606ace19 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -3,6 +3,7 @@
 #define LINUX_EXPORTFS_H 1
 
 #include <linux/types.h>
+#include <linux/path.h>
 
 struct dentry;
 struct iattr;
@@ -10,7 +11,6 @@ struct inode;
 struct iomap;
 struct super_block;
 struct vfsmount;
-struct path;
 
 /* limit the handle size to NFSv4 handle size now */
 #define MAX_HANDLE_SZ 128
@@ -157,6 +157,17 @@ struct fid {
 	};
 };
 
+enum handle_to_path_flags {
+	HANDLE_CHECK_PERMS   = (1 << 0),
+	HANDLE_CHECK_SUBTREE = (1 << 1),
+};
+
+struct handle_to_path_ctx {
+	struct path root;
+	enum handle_to_path_flags flags;
+	unsigned int fh_flags;
+};
+
 #define EXPORT_FH_CONNECTABLE	0x1 /* Encode file handle with parent */
 #define EXPORT_FH_FID		0x2 /* File handle may be non-decodeable */
 #define EXPORT_FH_DIR_ONLY	0x4 /* Only decode file handle for a directory */
@@ -226,6 +237,9 @@ struct fid {
  *    is also a directory.  In the event that it cannot be found, or storage
  *    space cannot be allocated, a %ERR_PTR should be returned.
  *
+ * permission:
+ *    Allow filesystems to specify a custom permission function.
+ *
  * open:
  *    Allow filesystems to specify a custom open function.
  *
@@ -255,6 +269,7 @@ struct export_operations {
 			  bool write, u32 *device_generation);
 	int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
 			     int nr_iomaps, struct iattr *iattr);
+	int (*permission)(struct handle_to_path_ctx *ctx, unsigned int oflags);
 	struct file * (*open)(struct path *path, unsigned int oflags);
 #define	EXPORT_OP_NOWCC			(0x1) /* don't collect v3 wcc data */
 #define	EXPORT_OP_NOSUBTREECHK		(0x2) /* no subtree checking */