[PATCH v2] pstore: add a KHO backend

[Michał Cłapiński]

On Fri, Jun 12, 2026 at 7:21 PM Pasha Tatashin
<pasha.tatashin at soleen.com> wrote:
>
> On 06-12 17:42, Mike Rapoport wrote:
> > Hi,
> >
> > On Fri, Jun 05, 2026 at 02:10:40PM +0200, Michal Clapinski wrote:
> > > Up to this point to preserve late shutdown logs in memory, users had to
> > > predefine a memory region using ramoops. This commit changes this by
> > > preserving a buffer using kexec-handover.
> > >
> > > pstore_kho supports preserving only 1 dmesg buffer.
> > > It gets replaced with the new buffer on every kexec, so the user has to
> > > copy the file out of pstore after every kexec.
> > > There is no erase() support.
> >
> > Sorry I didn't jump at v1.
> >
> > pstore does not really need a KHO backend. It can use ram backend with
> > reserve_mem and reserve_mem can be preserved with KHO already.
>
> I just tested it, and it works well, I think it would be fine for
> Google's requirements:
>
> CONFIG_PSTORE=y
> CONFIG_PSTORE_RAM=y
> CONFIG_PSTORE_CONSOLE=y

Is it common to write to this console? I think what I typically see in
the console are error logs that are also in dmesg, so if I preserve
console logs and dmesg I just have 2 files where one is a subset of
lines from the other.

> With the following parameters:
> 'reserve_mem=2M:2M:dmesg_buffer ramoops.mem_name=dmesg_buffer ramoops.max_reason=5 ramoops.console_size=2097152 ramoops.record_size=0 ramoops.ftrace_size=0 ramoops.pmsg_size=0'
>
> KHO preserves pstore properly. However, we need one patch that would
> allow for ramoops console to capture the output even when quiet is
> provided.
>
> Pasha