[PATCH 1/6] fhandle: create helper for name_to_handle_at(2)

[Thomas Bertschinger <tahbertschinger@gmail.com>]

Create a helper do_name_to_handle_at() that takes an additional argument,
lookup_flags, beyond the syscall arguments.

Because name_to_handle_at(2) doesn't take any lookup flags, it always
passes 0 for this argument.

Future callers like io_uring may pass LOOKUP_CACHED in order to request
a non-blocking lookup.

This helper's name is confusingly similar to do_sys_name_to_handle()
which takes care of returning the file handle, once the filename has
been turned into a struct path. To distinguish the names more clearly,
rename the latter to do_path_to_handle().

Signed-off-by: Thomas Bertschinger <tahbertschinger@gmail.com>
---
 fs/fhandle.c  | 61 ++++++++++++++++++++++++++++-----------------------
 fs/internal.h |  7 ++++++
 2 files changed, 41 insertions(+), 27 deletions(-)

diff --git a/fs/fhandle.c b/fs/fhandle.c
index 7c236f64cdea..57da648ca866 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -14,10 +14,10 @@
 #include "internal.h"
 #include "mount.h"
 
-static long do_sys_name_to_handle(const struct path *path,
-				  struct file_handle __user *ufh,
-				  void __user *mnt_id, bool unique_mntid,
-				  int fh_flags)
+static long do_path_to_handle(const struct path *path,
+			      struct file_handle __user *ufh,
+			      void __user *mnt_id, bool unique_mntid,
+			      int fh_flags)
 {
 	long retval;
 	struct file_handle f_handle;
@@ -111,27 +111,11 @@ static long do_sys_name_to_handle(const struct path *path,
 	return retval;
 }
 
-/**
- * sys_name_to_handle_at: convert name to handle
- * @dfd: directory relative to which name is interpreted if not absolute
- * @name: name that should be converted to handle.
- * @handle: resulting file handle
- * @mnt_id: mount id of the file system containing the file
- *          (u64 if AT_HANDLE_MNT_ID_UNIQUE, otherwise int)
- * @flag: flag value to indicate whether to follow symlink or not
- *        and whether a decodable file handle is required.
- *
- * @handle->handle_size indicate the space available to store the
- * variable part of the file handle in bytes. If there is not
- * enough space, the field is updated to return the minimum
- * value required.
- */
-SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
-		struct file_handle __user *, handle, void __user *, mnt_id,
-		int, flag)
+long do_name_to_handle_at(int dfd, const char __user *name,
+			  struct file_handle __user *handle, void __user *mnt_id,
+			  int flag, int lookup_flags)
 {
 	struct path path;
-	int lookup_flags;
 	int fh_flags = 0;
 	int err;
 
@@ -155,19 +139,42 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
 	else if (flag & AT_HANDLE_CONNECTABLE)
 		fh_flags |= EXPORT_FH_CONNECTABLE;
 
-	lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
+	if (flag & AT_SYMLINK_FOLLOW)
+		lookup_flags |= LOOKUP_FOLLOW;
 	if (flag & AT_EMPTY_PATH)
 		lookup_flags |= LOOKUP_EMPTY;
 	err = user_path_at(dfd, name, lookup_flags, &path);
 	if (!err) {
-		err = do_sys_name_to_handle(&path, handle, mnt_id,
-					    flag & AT_HANDLE_MNT_ID_UNIQUE,
-					    fh_flags);
+		err = do_path_to_handle(&path, handle, mnt_id,
+					flag & AT_HANDLE_MNT_ID_UNIQUE,
+					fh_flags);
 		path_put(&path);
 	}
 	return err;
 }
 
+/**
+ * sys_name_to_handle_at: convert name to handle
+ * @dfd: directory relative to which name is interpreted if not absolute
+ * @name: name that should be converted to handle.
+ * @handle: resulting file handle
+ * @mnt_id: mount id of the file system containing the file
+ *          (u64 if AT_HANDLE_MNT_ID_UNIQUE, otherwise int)
+ * @flag: flag value to indicate whether to follow symlink or not
+ *        and whether a decodable file handle is required.
+ *
+ * @handle->handle_size indicate the space available to store the
+ * variable part of the file handle in bytes. If there is not
+ * enough space, the field is updated to return the minimum
+ * value required.
+ */
+SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
+		struct file_handle __user *, handle, void __user *, mnt_id,
+		int, flag)
+{
+	return do_name_to_handle_at(dfd, name, handle, mnt_id, flag, 0);
+}
+
 static int get_path_anchor(int fd, struct path *root)
 {
 	if (fd >= 0) {
diff --git a/fs/internal.h b/fs/internal.h
index 38e8aab27bbd..af7e0810a90d 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -355,3 +355,10 @@ int anon_inode_getattr(struct mnt_idmap *idmap, const struct path *path,
 int anon_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 		       struct iattr *attr);
 void pidfs_get_root(struct path *path);
+
+/*
+ * fs/fhandle.c
+ */
+long do_name_to_handle_at(int dfd, const char __user *name,
+			  struct file_handle __user *handle,
+			  void __user *mnt_id, int flag, int lookup_flags);
-- 
2.50.1