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

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Date:   Thu, 1 Sep 2016 09:03:06 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     <virtio-dev@...ts.oasis-open.org>,
        <virtualization@...ts.linux-foundation.org>, <kvm@...r.kernel.org>,
        <qemu-devel@...gnu.org>, LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Anthony Liguori <aliguori@...zon.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Kees Cook <keescook@...omium.org>,
        Tony Luck <tony.luck@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Minchan Kim <minchan@...nel.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 1/3] virtio: Basic implementation of virtio pstore driver

Hi Michael,

On Wed, Aug 31, 2016 at 05:54:04PM +0300, Michael S. Tsirkin wrote:
> On Wed, Aug 31, 2016 at 05:08:00PM +0900, Namhyung Kim 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.
> > 
> > It supports legacy PCI device using single order-2 page buffer.  It uses
> > two virtqueues - one for (sync) read and another for (async) write.
> > Since it cannot wait for write finished, it supports up to 128
> > concurrent IO.  The buffer size is configurable now.
> > 
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: Radim Krčmář <rkrcmar@...hat.com>
> > Cc: "Michael S. Tsirkin" <mst@...hat.com>
> > Cc: Anthony Liguori <aliguori@...zon.com>
> > Cc: Anton Vorontsov <anton@...msg.org>
> > Cc: Colin Cross <ccross@...roid.com>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Tony Luck <tony.luck@...el.com>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Minchan Kim <minchan@...nel.org>
> > Cc: Will Deacon <will.deacon@....com>
> > Cc: kvm@...r.kernel.org
> > Cc: qemu-devel@...gnu.org
> > Cc: virtualization@...ts.linux-foundation.org
> > Cc: virtio-dev@...ts.oasis-open.org
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > ---

[SNIP]
> > +#define TYPE_TABLE_ENTRY(_entry)				\
> > +	{ PSTORE_TYPE_##_entry, VIRTIO_PSTORE_TYPE_##_entry }
> > +
> > +struct type_table {
> > +	int pstore;
> > +	u16 virtio;
> > +} type_table[] = {
> > +	TYPE_TABLE_ENTRY(DMESG),
> > +};
> > +
> > +#undef TYPE_TABLE_ENTRY
> > +
> > +
> > +static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
> > +{
> > +	unsigned int i;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(type_table); i++) {
> > +		if (type == type_table[i].pstore)
> > +			return cpu_to_virtio16(vps->vdev, type_table[i].virtio);
> 
> Does this pass sparse checks? If yes I'm surprised - this clearly
> returns a virtio16 type.

Ah, didn't run sparse.  Will change it to return a __le16 type
(according to your comment below).

> 
> 
> > +	}
> > +
> > +	return cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
> > +}
> > +
> > +static enum pstore_type_id from_virtio_type(struct virtio_pstore *vps, u16 type)

This one should be '__le16 type' as well.


> > +{
> > +	unsigned int i;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(type_table); i++) {
> > +		if (virtio16_to_cpu(vps->vdev, type) == type_table[i].virtio)
> > +			return type_table[i].pstore;
> > +	}
> > +
> > +	return PSTORE_TYPE_UNKNOWN;
> > +}
> > +

[SNIP]
> > +
> > +struct virtio_pstore_req {
> > +	__virtio16		cmd;
> > +	__virtio16		type;
> > +	__virtio32		flags;
> > +	__virtio64		id;
> > +	__virtio32		count;
> > +	__virtio32		reserved;
> > +};
> > +
> > +struct virtio_pstore_res {
> > +	__virtio16		cmd;
> > +	__virtio16		type;
> > +	__virtio32		ret;
> > +};
> 
> Is there a reason to support legacy endian-ness?
> If not, you can just use __le formats.

I just didn't know what's the preferred type.  Will change!

Thanks,
Namhyung

> 
> 
> > +struct virtio_pstore_fileinfo {
> > +	__virtio64		id;
> > +	__virtio32		count;
> > +	__virtio16		type;
> > +	__virtio16		unused;
> > +	__virtio32		flags;
> > +	__virtio32		len;
> > +	__virtio64		time_sec;
> > +	__virtio32		time_nsec;
> > +	__virtio32		reserved;
> > +};
> > +
> > +struct virtio_pstore_config {
> > +	__virtio32		bufsize;
> > +};
> > +
> > +#endif /* _LINUX_VIRTIO_PSTORE_H */
> > -- 
> > 2.9.3