[PATCH 4/6] fhandle: create __do_handle_open() helper

[Thomas Bertschinger <tahbertschinger@xxxxxxxxx>]

do_handle_open() takes care of both opening a file via its file handle,
and associating it with a file descriptor.

For io_uring, it is useful to do just the opening part separately,
because io_uring might not want to install it into the main open files
table when using fixed descriptors.

This creates a helper which will enable io_uring to do that.

Signed-off-by: Thomas Bertschinger <tahbertschinger@xxxxxxxxx>
---
 fs/fhandle.c  | 24 +++++++++++++++++-------
 fs/internal.h |  2 ++
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/fs/fhandle.c b/fs/fhandle.c
index dbb273a26214..b14884a93867 100644
--- a/fs/fhandle.c
+++ b/fs/fhandle.c
@@ -397,8 +397,8 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
 	return retval;
 }
 
-static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
-			   int open_flag)
+struct file *__do_handle_open(int mountdirfd, struct file_handle __user *ufh,
+			      int open_flag)
 {
 	long retval = 0;
 	struct path path __free(path_put) = {};
@@ -407,17 +407,27 @@ static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
 
 	retval = handle_to_path(mountdirfd, ufh, &path, open_flag);
 	if (retval)
-		return retval;
-
-	CLASS(get_unused_fd, fd)(open_flag);
-	if (fd < 0)
-		return fd;
+		return ERR_PTR(retval);
 
 	eops = path.mnt->mnt_sb->s_export_op;
 	if (eops->open)
 		file = eops->open(&path, open_flag);
 	else
 		file = file_open_root(&path, "", open_flag, 0);
+
+	return file;
+}
+
+static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
+			   int open_flag)
+{
+	struct file *file;
+
+	CLASS(get_unused_fd, fd)(open_flag);
+	if (fd < 0)
+		return fd;
+
+	file = __do_handle_open(mountdirfd, ufh, open_flag);
 	if (IS_ERR(file))
 		return PTR_ERR(file);
 
diff --git a/fs/internal.h b/fs/internal.h
index af7e0810a90d..26ac6f356313 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -362,3 +362,5 @@ void pidfs_get_root(struct path *path);
 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 file *__do_handle_open(int mountdirfd, struct file_handle __user *ufh,
+			      int open_flag);
-- 
2.50.1