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Re: [linux-lvm] blkid_wiping breaks snapshots

Dne 10.2.2014 10:30, Christian Hesse napsal(a):
Zdenek Kabelac <zkabelac redhat com> on Mon, 2014/02/10 09:33:
Dne 8.2.2014 00:55, Christian Hesse napsal(a):
Christian Hesse <list eworm de> on Sat, 2014/02/08 00:36:
Hello everybody,

I think I nailed it down with git bisect. My first bad commit is:

configure: enable blkid_wiping by default if the blkid library is present

Looks like this wipes data that is still needed... Building a package
with '--disable-blkid_wipe' now to verify on another system.

Uh, this only helps part of...

I changed my test setup and used writable snapshots. After that I got:

WARNING: DM_snapshot_cow signature detected on /dev/cvg/snap-home at
offset 0. Wipe it? [y/n]

(see https://bbs.archlinux.org/viewtopic.php?id=176504 for another report)

Looks like disabling blkid_wiping fixes this. My snapshot corruption still
occurs though. :-/
Bad thing about it is that the corruption does not occur reliable when
doing simple tests in 'git bisect'... Out of ideas for now - Will go to
bed now.

Now this was helpful, I guess I think what is going on.

Great! Waiting for patches then. :D

I could provide some more information when needed:

* This happens with read only snapshots only.
* I could reproduce with commit eaa23d32732c9bc3dd4f948781b5764cf21d84ba
   (wiping: add support for blkid wiping), so it was introduced there or

Should I investigate further or wait for something to test from you?

Is the patch bellow fixing your problem ?
(It's still not final - but should help)


diff --git a/tools/lvcreate.c b/tools/lvcreate.c
index 638a868..e8b1a7f 100644
--- a/tools/lvcreate.c
+++ b/tools/lvcreate.c
@@ -772,7 +772,7 @@ static int _read_activation_params(struct lvcreate_params *lp,
                                        LVM_READ | LVM_WRITE);

        /* Must not zero/wipe read only volume */
-       if (!(lp->permission & LVM_WRITE)) {
+       if (!lp->snapshot && !(lp->permission & LVM_WRITE)) {
                lp->zero = 0;
                lp->wipe_signatures = 0;

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