From db3b5b76a783ddcd247e9cf3299781167e75f9f9 Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@redhat.com>
Date: Wed, 1 Dec 2010 23:02:17 +0100
Subject: [PATCH] mount: read /sys for loopdev backing file

On systems without /etc/mtab (or everywhere if kernel >= 2.6.37)
we use loop autoclear flag and then the backing file name is not
stored in /etc/mtab. mount(8) uses sysfs to get the filename (or
LOOP_GET_STATU* ioctls on old kernels).

Signed-off-by: Karel Zak <kzak@redhat.com>
---
 mount/lomount.c | 27 +++++++++++++++++++++++++++
 mount/lomount.h |  7 +++++++
 mount/mount.c   | 30 +++++++++++++++++++++++++++---
 3 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/mount/lomount.c b/mount/lomount.c
index 90149536..4d99d9f6 100644
--- a/mount/lomount.c
+++ b/mount/lomount.c
@@ -109,6 +109,33 @@ static char *loopfile_from_sysfs(const char *device)
 	return res;
 }
 
+char *loopdev_get_loopfile(const char *device)
+{
+	char *res = loopfile_from_sysfs(device);
+
+	if (!res) {
+		struct loop_info lo;
+		struct loop_info64 lo64;
+		int fd;
+
+		if ((fd = open(device, O_RDONLY)) < 0)
+			return NULL;
+
+		if (ioctl(fd, LOOP_GET_STATUS64, &lo64) == 0) {
+			lo64.lo_file_name[LO_NAME_SIZE-2] = '*';
+			lo64.lo_file_name[LO_NAME_SIZE-1] = 0;
+			res = xstrdup((char *) lo64.lo_file_name);
+
+		} else if (ioctl(fd, LOOP_GET_STATUS, &lo) == 0) {
+			lo.lo_name[LO_NAME_SIZE-2] = '*';
+			lo.lo_name[LO_NAME_SIZE-1] = 0;
+			res = xstrdup((char *) lo.lo_name);
+		}
+		close(fd);
+	}
+	return res;
+}
+
 int
 is_loop_device (const char *device) {
 	struct stat st;
diff --git a/mount/lomount.h b/mount/lomount.h
index 59108d40..de8b76bf 100644
--- a/mount/lomount.h
+++ b/mount/lomount.h
@@ -1,3 +1,6 @@
+#ifndef UTIL_LINUX_LOMOUNT_H
+#define UTIL_LINUX_LOMOUNT_H
+
 extern int set_loop(const char *, const char *, unsigned long long, unsigned long long,
 		    const char *, int, int *);
 extern int del_loop(const char *);
@@ -7,6 +10,10 @@ extern char * find_unused_loop_device(void);
 
 extern int loopfile_used_with(char *devname, const char *filename, unsigned long long offset);
 extern char *loopfile_used (const char *filename, unsigned long long offset);
+extern char *loopdev_get_loopfile(const char *device);
+
 
 #define SETLOOP_RDONLY     (1<<0)  /* Open loop read-only */
 #define SETLOOP_AUTOCLEAR  (1<<1)  /* Automatically detach loop on close (2.6.25?) */
+
+#endif /* !UTIL_LINUX_LOMOUNT_H */
diff --git a/mount/mount.c b/mount/mount.c
index 9faa6a5b..8c30263c 100644
--- a/mount/mount.c
+++ b/mount/mount.c
@@ -249,9 +249,23 @@ parse_string_opt(char *s) {
 /* Report on a single mount.  */
 static void
 print_one (const struct my_mntent *me) {
+
+	char *fsname = NULL;
+
 	if (mount_quiet)
 		return;
-	printf ("%s on %s", me->mnt_fsname, me->mnt_dir);
+
+	/* users assume backing file name rather than /dev/loopN in
+	 * mount(8) output if the device has been initialized by mount(8).
+	 */
+	if (strncmp(me->mnt_fsname, "/dev/loop", 9) == 0 &&
+	    is_loop_autoclear(me->mnt_fsname))
+		fsname = loopdev_get_loopfile(me->mnt_fsname);
+
+	if (!fsname)
+		fsname = (char *) me->mnt_fsname;
+
+	printf ("%s on %s", fsname, me->mnt_dir);
 	if (me->mnt_type != NULL && *(me->mnt_type) != '\0')
 		printf (" type %s", me->mnt_type);
 	if (me->mnt_opts != NULL)
@@ -1206,10 +1220,20 @@ loop_check(const char **spec, const char **type, int *flags,
       if (verbose)
 	printf(_("mount: skipping the setup of a loop device\n"));
     } else {
-      /* use autoclear loopdev on system without regular mtab only */
-      int loop_opts = mtab_is_writable() ? 0 : SETLOOP_AUTOCLEAR;
+      int loop_opts;
       int res;
 
+      /* since 2.6.37 we don't have to store backing filename to mtab
+       * because kernel provides the name in /sys
+       */
+      if (get_linux_version() >= KERNEL_VERSION(2, 6, 37) ||
+	  mtab_is_writable() == 0) {
+
+	if (verbose)
+	  printf(_("mount: enabling autoclear loopdev flag\n"));
+	loop_opts = SETLOOP_AUTOCLEAR;
+      }
+
       if (*flags & MS_RDONLY)
         loop_opts |= SETLOOP_RDONLY;
 
-- 
2.39.5