On Fri, Sep 07, 2007 at 12:40:24PM +0200, Matthias Koenig wrote:
> Karel Zak <kzak@xxxxxxxxxx> writes:
>
> >> # mount -oloop /tmp/volume /mnt/
> >> # mount -oloop /tmp/volume /mnt/
> >> # mount
> >> /tmp/volume on /mnt type ext2 (rw,loop=/dev/loop0)
> >> /tmp/volume on /mnt type ext2 (rw,loop=/dev/loop1)
> >
> > I know about this problem and it's "fixed" in Fedora util-linux
> > package (almost for two years)...
>
> Ah thanks, I did not realize this patch.
I'm not proud of this old patch. See below... There is not support
for offsets (and lo_node of course).
> > Doesn't have kernel all information? Why this is not disabled by
> > kernel? Why this issues should be resolved by an userspace util when
> > kernel supports it? Is it real problem for all filesystems? Doesn't
> > exist same issue with multipath devices (SANs)?
>
> Good point. I am really not sure if setting up two loop devices with
> identical parameters should be forbidden by the kernel. There might
> be reasons these are valid use cases?
People are crazy... :-)
BTW, "duplicate" loops (by mount(8)) are disabled in Fedora
4,5,6,7,8 and RHEL5 and I've never seen any bug report.
> Thats why I wanted to apply the check only for mount -oloop to
> avoid two identical mounts as given in the example above.
> The problem here is that the mount is a two step process:
> 1. Setting up loop device, 2. mount, but appears transparently as
> one step to the user. However, the behaviour is different for normal block
> devices and loop devices. I think from a users POV mount should
> behave consistently.
Yes, I agree.
> > Maybe we can add a warning message to losetup only. The losetup
> > shouldn't be more "smart" than kernel or end-user -- I'd like to
> > follow kernel in this case.
> Yes, I agree. losetup as a low level tool shouldn't be smarter
> than the user and only be restricted by the kernel itself.
> I haven't been thinking about losetup itself, but the mount -oloop
> case.
OK. I look forward to your patches.
Karel
--- util-linux-ng-2.13-rc3/mount/fstab.c.kzak 2007-07-31 12:39:42.000000000 +0200
+++ util-linux-ng-2.13-rc3/mount/fstab.c 2007-08-13 12:24:40.000000000 +0200
@@ -264,6 +264,27 @@
return (ct == 1);
}
+/*
+ * Given the loop file LOOPFILE, and the mount point DIR, check that
+ * same file is already mounted on same directory
+ *
+ * Don't forget there's
+ * /path/loopfile /path/dir loop=/dev/loop0
+ * in mtab for loop devices.
+ */
+int
+is_mounted_same_loopfile(const char *loopfile, const char *dir) {
+ struct mntentchn *mc, *mc0;
+ int ct = 0;
+
+ mc0 = mtab_head();
+ for (mc = mc0->prev; mc && mc != mc0; mc = mc->prev)
+ if (streq(mc->m.mnt_fsname, loopfile) &&
+ streq(mc->m.mnt_dir, dir))
+ ct++;
+ return (ct == 1);
+}
+
/* Given the name FILE, try to find the option "loop=FILE" in mtab. */
struct mntentchn *
getmntoptfile (const char *file) {
--- util-linux-ng-2.13-rc3/mount/fstab.h.kzak 2007-05-30 10:18:12.000000000 +0200
+++ util-linux-ng-2.13-rc3/mount/fstab.h 2007-08-13 12:24:40.000000000 +0200
@@ -5,6 +5,7 @@
int mtab_is_writable(void);
int mtab_does_not_exist(void);
int is_mounted_once(const char *name);
+int is_mounted_same_loopfile(const char *loopfile, const char *dir);
struct mntentchn {
struct mntentchn *nxt, *prev;
--- util-linux-ng-2.13-rc3/mount/mount.c.kzak 2007-08-13 12:23:13.000000000 +0200
+++ util-linux-ng-2.13-rc3/mount/mount.c 2007-08-13 12:29:01.000000000 +0200
@@ -853,7 +853,7 @@
static int
loop_check(const char **spec, const char **type, int *flags,
- int *loop, const char **loopdev, const char **loopfile) {
+ int *loop, const char **loopdev, const char **loopfile, const char *dir) {
int looptype;
unsigned long long offset;
@@ -894,6 +894,10 @@
offset = opt_offset ? strtoull(opt_offset, NULL, 0) : 0;
+ if (is_mounted_same_loopfile(*loopfile, dir)) {
+ error(_("mount: %s already mounted on %s"), *loopfile, dir);
+ return EX_FAIL;
+ }
do {
if (!*loopdev || !**loopdev)
*loopdev = find_unused_loop_device();
@@ -1079,7 +1083,7 @@
* stale assignments of files to loop devices. Nasty when used for
* encryption.
*/
- res = loop_check(&spec, &types, &flags, &loop, &loopdev, &loopfile);
+ res = loop_check(&spec, &types, &flags, &loop, &loopdev, &loopfile, node);
if (res)
goto out;
}
-
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