fs: create helper file_user_path() for user displayed mapped file path

Overlayfs uses backing files with "fake" overlayfs f_path and "real"
underlying f_inode, in order to use underlying inode aops for mapped
files and to display the overlayfs path in /proc/<pid>/maps.

In preparation for storing the overlayfs "fake" path instead of the
underlying "real" path in struct backing_file, define a noop helper
file_user_path() that returns f_path for now.

Use the new helper in procfs and kernel logs whenever a path of a
mapped file is displayed to users.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20231009153712.1566422-3-amir73il@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
index d5b3ed2c58f5..c380d8c30704 100644
--- a/arch/arc/kernel/troubleshoot.c
+++ b/arch/arc/kernel/troubleshoot.c
@@ -90,10 +90,12 @@ static void show_faulting_vma(unsigned long address)
 	 */
 	if (vma) {
 		char buf[ARC_PATH_MAX];
-		char *nm = "?";
+		char *nm = "anon";
 
 		if (vma->vm_file) {
-			nm = file_path(vma->vm_file, buf, ARC_PATH_MAX-1);
+			/* XXX: can we use %pD below and get rid of buf? */
+			nm = d_path(file_user_path(vma->vm_file), buf,
+				    ARC_PATH_MAX-1);
 			if (IS_ERR(nm))
 				nm = "?";
 		}