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Re: kern/53616: dom0 crashes when dumping domU images with vnd+fss
The following reply was made to PR kern/53616; it has been noted by GNATS.
From: Robert Elz <kre%munnari.OZ.AU@localhost>
To: =?UTF-8?Q?Fr=C3=A9d=C3=A9ric_Fauberteau?= <triaxx%NetBSD.org@localhost>
Subject: Re: kern/53616: dom0 crashes when dumping domU images with vnd+fss
Date: Wed, 19 Sep 2018 13:37:18 +0700
Date: Wed, 19 Sep 2018 07:03:28 +0200
From: =3D?UTF-8?Q?Fr=3DC3=3DA9d=3DC3=3DA9ric_Fauberteau?=3D <t=
=7C Yes they run. But my idea was to not modify the mounted fs and to d=
As Manuel indicated, the issue is that making the snapshot itself modifie=
the filesystem - I have no idea how linux might cope otherwise, but the
filesystem (and the OS that is actually using it) needs to act differentl=
there'=5Bs a snapshot, as it needs to preserve the previous data, rather =
simply overwriting it. Hence, it has to know that the snapshot has been=
made, and making one while a system is running cannot possibly work.
It is possible that snapshotting an LVM might work, though I have no idea=
if we support that - thyat would basically modify the block map undernea=
the filesystem, and should be possible (if implemented...) Bit not the
=7C I will test again by explicitly mounting my fs in read-only mode.
If you mean mounting the fs via a vnd read only, no, that won't help.
It might let you access the filesystem without causing the rest of the
system to fail, but that system would not remain consistent, and your
backup would likely be nonsense. If you meant moounting the snapshot
read only, I don't think there's a choice - whether you give the read
only option or not, that's what happens anyway (and that would not
=7C Maybe I misunderstand and one of the commands I used does syscalls =
=7C modify fs.
Yes, the ones that make the snapshot.
Manuel's idea of snapshotting the filesystem that contains the images of =
files that are the backing store (if you are using file based storage) is=
probably the best that you can currently expect to worl. If your system=
mapping partitions though, that won't work.
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