Re: [PATCH 7/8] pstore: Remove needless lock during console writes

[Joel Fernandes]

On Fri, Nov 02, 2018 at 01:40:06PM -0700, Kees Cook wrote:
> On Fri, Nov 2, 2018 at 11:32 AM, Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote:
> > On Thu, Nov 01, 2018 at 04:51:59PM -0700, Kees Cook wrote:
> >> Since commit 70ad35db3321 ("pstore: Convert console write to use
> >> ->write_buf"), the console writer does not use the preallocated crash
> >> dump buffer any more, so there is no reason to perform locking around it.
> >
> > Out of curiosity, what was the reason for having this preallocated crash
> > buffer in the first place? I thought the 'console' type only did regular
> > kernel console logging, not crash dumps.
> 
> The primary reason is that the dumper needs to write to somewhere and
> we don't know the state of the system (memory allocation may not work
> for example).
> 
> The other frontends tend to run at "sane" locations in the kernel. The
> dumper, however, is quite fragile.

Makes sense. thanks.

> > Also I wonder if Namhyung is still poking around that virtio pstore driver he
> > mentioned in the commit mentioned above. :)
> 
> Did that never land? I thought it mostly had to happen at the qemu end?
> 
> With nvdimm emulation, we can just use ramoops. :)
> 

Yes it seems like it never landed: https://lwn.net/Articles/694742/

One of the nice thing about his virtio set though, vs the nvdimm way is that
he actually gets a directory on the host instead of a backing memory file.
Then he can just list this directory and see all the pstore files as he shows
in his example.

I guess it should not be too hard to write a tool to post-process the nvdimm
images and convert it to files anyway :)

thanks,

 - Joel