From c1fb95a3d859a2bbccbdf333363d518ba9b798d7 Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Tue, 19 Mar 2024 11:20:22 -0500
Subject: [PATCH] Teach mount to show file= option when displaying loopback
 mounts.

---
 toys/lsb/mount.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/toys/lsb/mount.c b/toys/lsb/mount.c
index 9fbd432c..2b397f34 100644
--- a/toys/lsb/mount.c
+++ b/toys/lsb/mount.c
@@ -373,13 +373,28 @@ void mount_main(void)
   // show mounts from /proc/mounts
   } else if (!dev) {
     for (mtl = xgetmountlist(0); mtl && (mm = dlist_pop(&mtl)); free(mm)) {
-      char *s = 0;
+      char *s = mm->device, *ss = "";
+      struct stat st;
 
       if (TT.t && strcmp(TT.t, mm->type)) continue;
-      if (*mm->device == '/') s = xabspath(mm->device, 0);
-      xprintf("%s on %s type %s (%s)\n",
-              s ? s : mm->device, mm->dir, mm->type, mm->opts);
-      free(s);
+      if (*s == '/') {
+        s = xabspath(mm->device, 0);
+        if (!stat(s, &st) && S_ISBLK(st.st_mode) &&dev_major(st.st_rdev)==7) {
+          char *temp = xmprintf("/sys/block/loop%d/loop/backing_file",
+            dev_minor(st.st_rdev));
+
+          ss = chomp(readfile(temp, 0, 0));
+          free(temp);
+          if (ss) {
+            temp = xmprintf(",file=%s"+!*mm->opts, ss);
+            free(ss);
+            ss = temp;
+          }
+        }
+      }
+      xprintf("%s on %s type %s (%s%s)\n", s, mm->dir, mm->type, mm->opts, ss);
+      if (s != mm->device) free(s);
+      if (*ss) free(ss);
     }
 
   // two arguments
-- 
2.39.2