Re: [PATCH 1/3] virtio: Basic implementation of virtio pstore driver

From: Namhyung Kim
Date: Mon Jul 18 2016 - 04:31:03 EST


Hello,

On Mon, Jul 18, 2016 at 09:54:39AM +0200, Cornelia Huck wrote:
> On Mon, 18 Jul 2016 13:37:39 +0900
> Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> > The virtio pstore driver provides interface to the pstore subsystem so
> > that the guest kernel's log/dump message can be saved on the host
> > machine. Users can access the log file directly on the host, or on the
> > guest at the next boot using pstore filesystem. It currently deals with
> > kernel log (printk) buffer only, but we can extend it to have other
> > information (like ftrace dump) later.
>
> Like the idea.

Thanks!

>
> >
> > It supports legacy PCI device using single order-2 page buffer. As all
>
> There should not be anything in there that limits this to pci, no?

Yep, there's no restriction AFAIK. I just choose it to implement the poc
code quickly.

>
> > operation of pstore is synchronous, it would be fine IMHO. However I
> > don't know how to make write operation synchronous since it's called
> > with a spinlock held (from any context including NMI).
> >
> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Cc: Radim Kr??m???? <rkrcmar@xxxxxxxxxx>
> > Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> > Cc: Anthony Liguori <aliguori@xxxxxxxxxx>
> > Cc: Anton Vorontsov <anton@xxxxxxxxxx>
> > Cc: Colin Cross <ccross@xxxxxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: Tony Luck <tony.luck@xxxxxxxxx>
> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Minchan Kim <minchan@xxxxxxxxxx>
> > Cc: kvm@xxxxxxxxxxxxxxx
> > Cc: qemu-devel@xxxxxxxxxx
> > Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> > ---
> > drivers/virtio/Kconfig | 10 ++
> > drivers/virtio/Makefile | 1 +
> > drivers/virtio/virtio_pstore.c | 317 +++++++++++++++++++++++++++++++++++++
> > include/uapi/linux/Kbuild | 1 +
> > include/uapi/linux/virtio_ids.h | 1 +
> > include/uapi/linux/virtio_pstore.h | 53 +++++++
> > 6 files changed, 383 insertions(+)
> > create mode 100644 drivers/virtio/virtio_pstore.c
> > create mode 100644 include/uapi/linux/virtio_pstore.h
> >
>
> (...)
>
> > diff --git a/drivers/virtio/virtio_pstore.c b/drivers/virtio/virtio_pstore.c
> > new file mode 100644
> > index 000000000000..6fe62c0f1508
> > --- /dev/null
> > +++ b/drivers/virtio/virtio_pstore.c
> > @@ -0,0 +1,317 @@
> > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/pstore.h>
> > +#include <linux/virtio.h>
> > +#include <linux/virtio_config.h>
> > +#include <uapi/linux/virtio_ids.h>
> > +#include <uapi/linux/virtio_pstore.h>
> > +
> > +#define VIRT_PSTORE_ORDER 2
> > +#define VIRT_PSTORE_BUFSIZE (4096 << VIRT_PSTORE_ORDER)
>
> It may make sense to make the size of the buffer configurable through
> the config space.

Right. I'm considering it too, but it needs a buffer larger than
kmsg_bytes (= 10K) to work properly in the current implementation. As
this version is just to verify the idea is sane and useful, I used a
fixed size buffer. Will change in the next version.

>
> (...)
>
> > diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> > index 77925f587b15..cba63225d85a 100644
> > --- a/include/uapi/linux/virtio_ids.h
> > +++ b/include/uapi/linux/virtio_ids.h
> > @@ -41,5 +41,6 @@
> > #define VIRTIO_ID_CAIF 12 /* Virtio caif */
> > #define VIRTIO_ID_GPU 16 /* virtio GPU */
> > #define VIRTIO_ID_INPUT 18 /* virtio input */
> > +#define VIRTIO_ID_PSTORE 19 /* virtio pstore */
>
> This id is already used by one of the new device types queued but not
> yet in the standard. IIRC, 22 is the next free one.

Ok, will update.

>
> Speaking of the standard: I think it makes sense to at least reserve a
> device id for pstore, as the idea is sound. Maybe prepare a patch to
> the standard as well if you have time?

I'd love to. As I mentioned earlier, I don't have enough knowledge in
this area. Could you please provide some links about how can I do that?

Thanks,
Namhyung