Merge patch series "pidfs: implement file handle support"

Christian Brauner <brauner@kernel.org> says:

Now that we have the preliminaries to lookup struct pid based on its
inode number alone we can implement file handle support.

This is based on custom export operation methods which allows pidfs to
implement permission checking and opening of pidfs file handles cleanly
without hacking around in the core file handle code too much.

* patches from https://lore.kernel.org/r/20241129-work-pidfs-file_handle-v1-0-87d803a42495@kernel.org:
  pidfs: implement file handle support
  exportfs: add permission method
  fhandle: pull CAP_DAC_READ_SEARCH check into may_decode_fh()
  exportfs: add open method
  fhandle: simplify error handling
  pseudofs: add support for export_ops

Link: https://lore.kernel.org/r/20241129-work-pidfs-file_handle-v1-0-87d803a42495@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index 4cc8801e50e3..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;
@@ -156,6 +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 */
@@ -225,6 +237,12 @@ 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.
+ *
  * commit_metadata:
  *    @commit_metadata should commit metadata changes to stable storage.
  *
@@ -251,6 +269,8 @@ 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 */
 #define	EXPORT_OP_CLOSE_BEFORE_UNLINK	(0x4) /* close files before unlink */
diff --git a/include/linux/pseudo_fs.h b/include/linux/pseudo_fs.h
index 730f77381d55..2503f7625d65 100644
--- a/include/linux/pseudo_fs.h
+++ b/include/linux/pseudo_fs.h
@@ -5,6 +5,7 @@
 
 struct pseudo_fs_context {
 	const struct super_operations *ops;
+	const struct export_operations *eops;
 	const struct xattr_handler * const *xattr;
 	const struct dentry_operations *dops;
 	unsigned long magic;