Re: [PATCH v2 qemu 0/3] Allow dump-guest-memory to output standard kdump format

[Daniel P . Berrangé]

On Wed, Sep 13, 2023 at 06:03:12PM -0700, Stephen Brennan wrote:
> Hello all,
> 
> This is the second version of my patch series about the kdump format,
> you can see the first version here [1].
> 
> The current output format for dump-guest-memory's kdump compressed
> format is actually the "makedumpfile flattened" format. It was done
> intentionally to allow the flexibility to write to non-seekable file
> descriptors, like pipes [2], without using temporary files. Currently
> libvirt uses this ability when VIR_DUMP_BYPASS_CACHE flag is set, to
> avoid the dump process using page cache. The standard kdump output
> format needs the page cache so that it can seek back and forth as part
> of writing the dump file.
> 
> So the default kdump dump format cannot be changed to the standard
> format. This patch series adds the ability to use the standard format,
> and adds a QMP / HMP argument to enable it.
> 
> An open question for Daniel et al.:
> 
> Would it be possible to make flattened the default only for libvirt? I
> totally agree that this would be a bad backward incompatible change
> there. But for QMP / HMP commands, I think using the standard, broadly
> compatible format as the default is important for user friendliness. If
> a user needs to know the difference between flavors of kdump formats
> like the flattened format, in order to set the correct option, then
> we've already lost.

The default is 'elf' - any use of kdump formats is already an opt-in,
and with the new kdump variants represented as enums, the user can
just specify which they want explicitly.


With regards,
Daniel
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