Re: [PATCH 0/4] Allow xml-configured coredump format on VM crash
On Fri, Mar 28, 2025 at 05:45:12PM +0100, Denis V. Lunev via Devel wrote:
On 3/27/25 11:14, Nikolai Barybin wrote:
> When libvirt processes VM crash event it always dumps core in raw
> format.
>
> This series makes it possible to configure dump format via domain xml.
> This would be especcialy helpful for Windows guests, because it requires
> a lot effort to convert raw dump into wingdb.
>
> Nikolai Barybin (4):
> conf: schemas: add coredump_format element to events section
> src: conf: add parsing/formatting for 'coredump_format' value
> qemu: use configurable dump format in doCoreDumpToAutoDumpPath()
> docs: formatdomain: document 'coredump_format' element
>
> docs/formatdomain.rst | 9 +++++
> src/conf/domain_conf.c | 64 +++++++++++++++++++++++++++++++
> src/conf/domain_conf.h | 2 +
> src/conf/schemas/domaincommon.rng | 19 +++++++++
> src/libvirt_private.syms | 2 +
> src/qemu/qemu_driver.c | 2 +-
> 6 files changed, 97 insertions(+), 1 deletion(-)
>
The idea is that correct Windows dump could be collected
only at the moment of the dump collection as dump
collector code in QEMU uses some information from
Windows drivers. Later conversion using external tools
proven to be complex.
That is why we either should specify the type of the
dump inside the configuration file or autoguess the
format. I though that latter could be implemented as
the next step using f.e. presence of HyperV feature or
checking OS type in metadata.
I think that this thing would be useful.
Effectively QEMU has three dump formats - WinDump, KDump and ELF,
with the KDump format being overloaded to express 6 different
sub-variants.
The global qemu.conf setting is effectively useless as far as
the 'win-dmp' format goes, because it is highly unlikely to
have a single host running exclusively windows guests.
Anyone know if the KDump format is only interesting for Linux
guests, or can it be useful for dumping any guest OS types ?
Looking at the QEMU impl, IIUC the WinDump format can only be requested
if the guest OS has exposed the Win Dump note in fw_cfg via the vmcoreinfo
device, otherwise we'll hit a hard error on the check
if (s->guest_note_size != VMCOREINFO_WIN_DUMP_NOTE_SIZE32 &&
s->guest_note_size != VMCOREINFO_WIN_DUMP_NOTE_SIZE64) {
error_setg(errp, "win-dump: invalid vmcoreinfo note size");
return;
}
This in turn depends on whether the KVM guest drivers are installed in
the guest. IOW, we can't auto-choose WinDump merely based on presence
of the HyperV fature, nor even libosinfo OS type in metadata.
QEMU itself should always knows whether or not it can use WinDump format,
as it can see the fw_cfg data, but I can't see any way this is exposed
to the mgmt app, but potentially that could be expressed via a new qmp
command if needed ?
Essentially I'm wondering whether there's any pratical way we can
"do the right thing" without manual configuration of each guest ?
If it is just a choice between using win-dmp vs the qemu.conf setting
it might be doable, assuming the various kdump,elf formats are viable
for /all/ guest types. If we needed to auto-detct kdump vs elf it gets
harder
With regards,
Daniel
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