On Fri, Mar 24, 2023, at 18:26, Bjorn Andersson wrote:
> On Wed, Feb 15, 2023 at 04:05:36PM +0100, Arnd Bergmann wrote:
>> On Mon, Jan 30, 2023, at 23:24, Bjorn Andersson wrote:
>
> Iiuc pstore provides a place to store system state for analysis after a
> reboot, but DCC provides essentially register dumps on demand - with the
> system reset being a special case trigger.
>
> So I think it would look neat to expose the DCC data alongside other
> pstore data (except for the mentioned issues with ramoops not working on
> most Qualcomm devices), but when the reboot happens DCC captures data in
> the DCC SRAM, not in the pstore (whatever backing might be used). So
> post boot, something would need to get the DCC data into the pstore.
>
> To me this sounds in conflict with the pstore design.
Sorry for the late reply.
The case I was thinking of is making the DCC SRAM a pstore backend
that might be shared with other pstore users, in place of the
other targets like PSTORE_RAM, PSTORE_BLK, EFI_VARS_PSTORE and
the powerpc64 nvram. This might be a bad idea for other reasons of
course, e.g. if it's impossible to have more than one pstore
backend active and the SRAM is too small to contain the data
that would otherwise be store here, or if it's not persistent
enough.
> Further more, with the reboot trigger being the special case, we'd need
> to amend the pstore state in runtime to capture the case where the user
> requested the DCC to capture the state.
>
>
> One idea that I was looking at was to trigger a devcoredump as a way to
> get the data out of the kernel, instead of a new device node. But it
> doesn't seem to fit very well with existing use cases, and I haven't
> used DCC sufficiently - given that it doesn't exist upstream...
You are probably right, but I'm curious about DEV_COREDUMP, as I
haven't actually seen that before, and I can't seem to find any
documentation about what its intention is, though I can see a number
of in-kernel users.
> We made significant changes to the control interface through the review
> process, I think we have something that looks reasonable now, but I
> picked the patches under the premise that it's unstable and in debugfs,
> and exposing the tool to users could lead to more interest in
> polishing it.
Ok
Arnd
