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Re: [Qemu-devel] [PATCH 1/3] virtio: Basic implementation of virtio psto


From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH 1/3] virtio: Basic implementation of virtio pstore driver
Date: Tue, 13 Sep 2016 18:19:41 +0300

On Sat, Aug 20, 2016 at 05:07:42PM +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 <address@hidden>
> Cc: Radim Krčmář <address@hidden>
> Cc: "Michael S. Tsirkin" <address@hidden>
> Cc: Anthony Liguori <address@hidden>
> Cc: Anton Vorontsov <address@hidden>
> Cc: Colin Cross <address@hidden>
> Cc: Kees Cook <address@hidden>
> Cc: Tony Luck <address@hidden>
> Cc: Steven Rostedt <address@hidden>
> Cc: Ingo Molnar <address@hidden>
> Cc: Minchan Kim <address@hidden>
> Cc: address@hidden
> Cc: address@hidden
> Cc: address@hidden
> Signed-off-by: Namhyung Kim <address@hidden>
> ---
>  drivers/virtio/Kconfig             |  10 +
>  drivers/virtio/Makefile            |   1 +
>  drivers/virtio/virtio_pstore.c     | 417 
> +++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/Kbuild          |   1 +
>  include/uapi/linux/virtio_ids.h    |   1 +
>  include/uapi/linux/virtio_pstore.h |  74 +++++++
>  6 files changed, 504 insertions(+)
>  create mode 100644 drivers/virtio/virtio_pstore.c
>  create mode 100644 include/uapi/linux/virtio_pstore.h
> 
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 77590320d44c..8f0e6c796c12 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -58,6 +58,16 @@ config VIRTIO_INPUT
>  
>        If unsure, say M.
>  
> +config VIRTIO_PSTORE
> +     tristate "Virtio pstore driver"
> +     depends on VIRTIO
> +     depends on PSTORE
> +     ---help---
> +      This driver supports virtio pstore devices to save/restore
> +      panic and oops messages on the host.
> +
> +      If unsure, say M.
> +
>   config VIRTIO_MMIO
>       tristate "Platform bus driver for memory mapped virtio devices"
>       depends on HAS_IOMEM && HAS_DMA
> diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> index 41e30e3dc842..bee68cb26d48 100644
> --- a/drivers/virtio/Makefile
> +++ b/drivers/virtio/Makefile
> @@ -5,3 +5,4 @@ virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
>  virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
>  obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
>  obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
> +obj-$(CONFIG_VIRTIO_PSTORE) += virtio_pstore.o
> diff --git a/drivers/virtio/virtio_pstore.c b/drivers/virtio/virtio_pstore.c
> new file mode 100644
> index 000000000000..0a63c7db4278
> --- /dev/null
> +++ b/drivers/virtio/virtio_pstore.c
> @@ -0,0 +1,417 @@
> +#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)
> +#define VIRT_PSTORE_NR_REQ   128

where are these numbers from?


> +
> +struct virtio_pstore {
> +     struct virtio_device    *vdev;
> +     struct virtqueue        *vq[2];
> +     struct pstore_info       pstore;
> +     struct virtio_pstore_req req[VIRT_PSTORE_NR_REQ];
> +     struct virtio_pstore_res res[VIRT_PSTORE_NR_REQ];
> +     unsigned int             req_id;
> +
> +     /* Waiting for host to ack */
> +     wait_queue_head_t       acked;
> +     int                     failed;
> +};
> +
> +#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

Let's not play preprocessor games until this becomes
a big issue. Simple
{ PSTORE_TYPE_DMESG, VIRTIO_PSTORE_TYPE_DMESG}
does the trick just as well for now.
Also see below.



> +
> +

single empty line pls.

> +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);
> +     }

Rather complex for something that always returns a single value.
why do we need a table at all?
How about a switch statement?

static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
{
    switch (type) {
    case PSTORE_TYPE_DMESG:
        return VIRTIO_PSTORE_TYPE_DMESG;
    default:
        return VIRTIO_PSTORE_TYPE_UNKNOWN;
    }
}


> +
> +     return cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
> +}

This returns an incorrect type.


> +
> +static enum pstore_type_id from_virtio_type(struct virtio_pstore *vps, u16 
> type)
> +{
> +     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;
> +}
> +
> +static void virtpstore_ack(struct virtqueue *vq)
> +{
> +     struct virtio_pstore *vps = vq->vdev->priv;
> +
> +     wake_up(&vps->acked);
> +}
> +
> +static void virtpstore_check(struct virtqueue *vq)
> +{
> +     struct virtio_pstore *vps = vq->vdev->priv;
> +     struct virtio_pstore_res *res;
> +     unsigned int len;
> +
> +     res = virtqueue_get_buf(vq, &len);
> +     if (res == NULL)
> +             return;
> +
> +     if (virtio32_to_cpu(vq->vdev, res->ret) < 0)
> +             vps->failed = 1;
> +}
> +
> +static void virt_pstore_get_reqs(struct virtio_pstore *vps,
> +                              struct virtio_pstore_req **preq,
> +                              struct virtio_pstore_res **pres)
> +{
> +     unsigned int idx = vps->req_id++ % VIRT_PSTORE_NR_REQ;
> +
> +     *preq = &vps->req[idx];
> +     *pres = &vps->res[idx];
> +
> +     memset(*preq, 0, sizeof(**preq));
> +     memset(*pres, 0, sizeof(**pres));
> +}
> +
> +static int virt_pstore_open(struct pstore_info *psi)
> +{
> +     struct virtio_pstore *vps = psi->data;
> +     struct virtio_pstore_req *req;
> +     struct virtio_pstore_res *res;
> +     struct scatterlist sgo[1], sgi[1];
> +     struct scatterlist *sgs[2] = { sgo, sgi };
> +     unsigned int len;
> +
> +     virt_pstore_get_reqs(vps, &req, &res);
> +
> +     req->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_OPEN);
> +
> +     sg_init_one(sgo, req, sizeof(*req));
> +     sg_init_one(sgi, res, sizeof(*res));
> +     virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
> +     virtqueue_kick(vps->vq[0]);
> +
> +     wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
> +     return virtio32_to_cpu(vps->vdev, res->ret);
> +}
> +
> +static int virt_pstore_close(struct pstore_info *psi)
> +{
> +     struct virtio_pstore *vps = psi->data;
> +     struct virtio_pstore_req *req = &vps->req[vps->req_id];
> +     struct virtio_pstore_res *res = &vps->res[vps->req_id];
> +     struct scatterlist sgo[1], sgi[1];
> +     struct scatterlist *sgs[2] = { sgo, sgi };
> +     unsigned int len;
> +
> +     virt_pstore_get_reqs(vps, &req, &res);
> +
> +     req->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_CLOSE);
> +
> +     sg_init_one(sgo, req, sizeof(*req));
> +     sg_init_one(sgi, res, sizeof(*res));
> +     virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
> +     virtqueue_kick(vps->vq[0]);
> +
> +     wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
> +     return virtio32_to_cpu(vps->vdev, res->ret);
> +}
> +
> +static ssize_t virt_pstore_read(u64 *id, enum pstore_type_id *type,
> +                             int *count, struct timespec *time,
> +                             char **buf, bool *compressed,
> +                             ssize_t *ecc_notice_size,
> +                             struct pstore_info *psi)
> +{
> +     struct virtio_pstore *vps = psi->data;
> +     struct virtio_pstore_req *req;
> +     struct virtio_pstore_res *res;
> +     struct virtio_pstore_fileinfo info;
> +     struct scatterlist sgo[1], sgi[3];
> +     struct scatterlist *sgs[2] = { sgo, sgi };
> +     unsigned int len;
> +     unsigned int flags;
> +     int ret;
> +     void *bf;
> +
> +     virt_pstore_get_reqs(vps, &req, &res);
> +
> +     req->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_READ);
> +
> +     sg_init_one(sgo, req, sizeof(*req));
> +     sg_init_table(sgi, 3);
> +     sg_set_buf(&sgi[0], res, sizeof(*res));
> +     sg_set_buf(&sgi[1], &info, sizeof(info));
> +     sg_set_buf(&sgi[2], psi->buf, psi->bufsize);
> +     virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
> +     virtqueue_kick(vps->vq[0]);
> +
> +     wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
> +     if (len < sizeof(*res) + sizeof(info))
> +             return -1;
> +
> +     ret = virtio32_to_cpu(vps->vdev, res->ret);
> +     if (ret < 0)
> +             return ret;
> +
> +     len = virtio32_to_cpu(vps->vdev, info.len);
> +
> +     bf = kmalloc(len, GFP_KERNEL);
> +     if (bf == NULL)
> +             return -ENOMEM;
> +
> +     *id    = virtio64_to_cpu(vps->vdev, info.id);
> +     *type  = from_virtio_type(vps, info.type);
> +     *count = virtio32_to_cpu(vps->vdev, info.count);
> +
> +     flags = virtio32_to_cpu(vps->vdev, info.flags);
> +     *compressed = flags & VIRTIO_PSTORE_FL_COMPRESSED;
> +
> +     time->tv_sec  = virtio64_to_cpu(vps->vdev, info.time_sec);
> +     time->tv_nsec = virtio32_to_cpu(vps->vdev, info.time_nsec);
> +
> +     memcpy(bf, psi->buf, len);
> +     *buf = bf;
> +
> +     return len;
> +}
> +
> +static int notrace virt_pstore_write(enum pstore_type_id type,
> +                                  enum kmsg_dump_reason reason,
> +                                  u64 *id, unsigned int part, int count,
> +                                  bool compressed, size_t size,
> +                                  struct pstore_info *psi)
> +{
> +     struct virtio_pstore *vps = psi->data;
> +     struct virtio_pstore_req *req;
> +     struct virtio_pstore_res *res;
> +     struct scatterlist sgo[2], sgi[1];
> +     struct scatterlist *sgs[2] = { sgo, sgi };
> +     unsigned int flags = compressed ? VIRTIO_PSTORE_FL_COMPRESSED : 0;
> +
> +     if (vps->failed)
> +             return -1;
> +
> +     *id = vps->req_id;
> +     virt_pstore_get_reqs(vps, &req, &res);
> +
> +     req->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_WRITE);
> +     req->type  = to_virtio_type(vps, type);
> +     req->flags = cpu_to_virtio32(vps->vdev, flags);
> +
> +     sg_init_table(sgo, 2);
> +     sg_set_buf(&sgo[0], req, sizeof(*req));
> +     sg_set_buf(&sgo[1], pstore_get_buf(psi), size);
> +     sg_init_one(sgi, res, sizeof(*res));
> +     virtqueue_add_sgs(vps->vq[1], sgs, 1, 1, vps, GFP_ATOMIC);
> +     virtqueue_kick(vps->vq[1]);
> +
> +     return 0;
> +}
> +
> +static int virt_pstore_erase(enum pstore_type_id type, u64 id, int count,
> +                          struct timespec time, struct pstore_info *psi)
> +{
> +     struct virtio_pstore *vps = psi->data;
> +     struct virtio_pstore_req *req;
> +     struct virtio_pstore_res *res;
> +     struct scatterlist sgo[1], sgi[1];
> +     struct scatterlist *sgs[2] = { sgo, sgi };
> +     unsigned int len;
> +
> +     virt_pstore_get_reqs(vps, &req, &res);
> +
> +     req->cmd   = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_ERASE);
> +     req->type  = to_virtio_type(vps, type);
> +     req->id    = cpu_to_virtio64(vps->vdev, id);
> +     req->count = cpu_to_virtio32(vps->vdev, count);
> +
> +     sg_init_one(sgo, req, sizeof(*req));
> +     sg_init_one(sgi, res, sizeof(*res));
> +     virtqueue_add_sgs(vps->vq[0], sgs, 1, 1, vps, GFP_KERNEL);
> +     virtqueue_kick(vps->vq[0]);
> +
> +     wait_event(vps->acked, virtqueue_get_buf(vps->vq[0], &len));
> +     return virtio32_to_cpu(vps->vdev, res->ret);
> +}
> +
> +static int virt_pstore_init(struct virtio_pstore *vps)
> +{
> +     struct pstore_info *psinfo = &vps->pstore;
> +     int err;
> +
> +     if (!psinfo->bufsize)
> +             psinfo->bufsize = VIRT_PSTORE_BUFSIZE;
> +
> +     psinfo->buf = alloc_pages_exact(psinfo->bufsize, GFP_KERNEL);
> +     if (!psinfo->buf) {
> +             pr_err("cannot allocate pstore buffer\n");
> +             return -ENOMEM;
> +     }
> +
> +     psinfo->owner = THIS_MODULE;
> +     psinfo->name  = "virtio";
> +     psinfo->open  = virt_pstore_open;
> +     psinfo->close = virt_pstore_close;
> +     psinfo->read  = virt_pstore_read;
> +     psinfo->erase = virt_pstore_erase;
> +     psinfo->write = virt_pstore_write;
> +     psinfo->flags = PSTORE_FLAGS_DMESG;
> +
> +     psinfo->data  = vps;
> +     spin_lock_init(&psinfo->buf_lock);
> +
> +     err = pstore_register(psinfo);
> +     if (err)
> +             kfree(psinfo->buf);
> +
> +     return err;
> +}
> +
> +static int virt_pstore_exit(struct virtio_pstore *vps)
> +{
> +     struct pstore_info *psinfo = &vps->pstore;
> +
> +     pstore_unregister(psinfo);

I don't know enough about pstore - does this
actually ensure that
1. all existing users close the device
2. no new users can open it
somehow?

> +
> +     free_pages_exact(psinfo->buf, psinfo->bufsize);
> +     psinfo->buf = NULL;
> +     psinfo->bufsize = 0;
> +
> +     return 0;
> +}
> +
> +static int virtpstore_init_vqs(struct virtio_pstore *vps)
> +{
> +     vq_callback_t *callbacks[] = { virtpstore_ack, virtpstore_check };
> +     const char *names[] = { "pstore_read", "pstore_write" };
> +
> +     return vps->vdev->config->find_vqs(vps->vdev, 2, vps->vq,
> +                                        callbacks, names);
> +}
> +
> +static void virtpstore_init_config(struct virtio_pstore *vps)
> +{
> +     u32 bufsize;
> +
> +     virtio_cread(vps->vdev, struct virtio_pstore_config, bufsize, &bufsize);
> +
> +     vps->pstore.bufsize = PAGE_ALIGN(bufsize);
> +}
> +
> +static void virtpstore_confirm_config(struct virtio_pstore *vps)
> +{
> +     u32 bufsize = vps->pstore.bufsize;
> +
> +     virtio_cwrite(vps->vdev, struct virtio_pstore_config, bufsize,
> +                  &bufsize);
> +}
> +
> +static int virtpstore_probe(struct virtio_device *vdev)
> +{
> +     struct virtio_pstore *vps;
> +     int err;
> +
> +     if (!vdev->config->get) {
> +             dev_err(&vdev->dev, "driver init: config access disabled\n");
> +             return -EINVAL;
> +     }
> +
> +     vdev->priv = vps = kzalloc(sizeof(*vps), GFP_KERNEL);
> +     if (!vps) {
> +             err = -ENOMEM;
> +             goto out;
> +     }
> +     vps->vdev = vdev;
> +
> +     err = virtpstore_init_vqs(vps);
> +     if (err < 0)
> +             goto out_free;
> +
> +     virtpstore_init_config(vps);
> +
> +     err = virt_pstore_init(vps);
> +     if (err)
> +             goto out_del_vq;
> +
> +     virtpstore_confirm_config(vps);
> +
> +     init_waitqueue_head(&vps->acked);
> +
> +     virtio_device_ready(vdev);
> +
> +     dev_info(&vdev->dev, "driver init: ok (bufsize = %luK, flags = %x)\n",
> +              vps->pstore.bufsize >> 10, vps->pstore.flags);
> +
> +     return 0;
> +
> +out_del_vq:
> +     vdev->config->del_vqs(vdev);
> +out_free:
> +     kfree(vps);
> +out:
> +     dev_err(&vdev->dev, "driver init: failed with %d\n", err);
> +     return err;
> +}
> +
> +static void virtpstore_remove(struct virtio_device *vdev)
> +{
> +     struct virtio_pstore *vps = vdev->priv;
> +
> +     virt_pstore_exit(vps);
> +
> +     /* Now we reset the device so we can clean up the queues. */
> +     vdev->config->reset(vdev);
> +
> +     vdev->config->del_vqs(vdev);
> +
> +     kfree(vps);
> +}
> +
> +static unsigned int features[] = {
> +};
> +
> +static struct virtio_device_id id_table[] = {
> +     { VIRTIO_ID_PSTORE, VIRTIO_DEV_ANY_ID },
> +     { 0 },
> +};
> +
> +static struct virtio_driver virtio_pstore_driver = {

We need some way to avoid trying to load this
as a legacy device. There isn't a way to do it yet
so I won't block your patch on this but pls try to
come up with something, and I'll do, too.


> +     .driver.name         = KBUILD_MODNAME,
> +     .driver.owner        = THIS_MODULE,
> +     .feature_table       = features,
> +     .feature_table_size  = ARRAY_SIZE(features),
> +     .id_table            = id_table,
> +     .probe               = virtpstore_probe,
> +     .remove              = virtpstore_remove,

Won't this need freeze/restore callbacks?

> +};
> +
> +module_virtio_driver(virtio_pstore_driver);
> +MODULE_DEVICE_TABLE(virtio, id_table);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Namhyung Kim <address@hidden>");
> +MODULE_DESCRIPTION("Virtio pstore driver");
> diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
> index 6d4e92ccdc91..9bbb1554d8b2 100644
> --- a/include/uapi/linux/Kbuild
> +++ b/include/uapi/linux/Kbuild
> @@ -449,6 +449,7 @@ header-y += virtio_ids.h
>  header-y += virtio_input.h
>  header-y += virtio_net.h
>  header-y += virtio_pci.h
> +header-y += virtio_pstore.h
>  header-y += virtio_ring.h
>  header-y += virtio_rng.h
>  header-y += virtio_scsi.h
> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> index 77925f587b15..c72a9ab588c0 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       22 /* virtio pstore */
>  
>  #endif /* _LINUX_VIRTIO_IDS_H */
> diff --git a/include/uapi/linux/virtio_pstore.h 
> b/include/uapi/linux/virtio_pstore.h
> new file mode 100644
> index 000000000000..f4b0d204d8ae
> --- /dev/null
> +++ b/include/uapi/linux/virtio_pstore.h
> @@ -0,0 +1,74 @@
> +#ifndef _LINUX_VIRTIO_PSTORE_H
> +#define _LINUX_VIRTIO_PSTORE_H
> +/* This header is BSD licensed so anyone can use the definitions to implement
> + * compatible drivers/servers.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + * 1. Redistributions of source code must retain the above copyright
> + *    notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + *    notice, this list of conditions and the following disclaimer in the
> + *    documentation and/or other materials provided with the distribution.
> + * 3. Neither the name of IBM nor the names of its contributors
> + *    may be used to endorse or promote products derived from this software
> + *    without specific prior written permission.
> + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS 
> IS'' AND
> + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
> + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
> + * ARE DISCLAIMED.  IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
> + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
> + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
> + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
> + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
> + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
> + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
> + * SUCH DAMAGE. */
> +#include <linux/types.h>
> +#include <linux/virtio_types.h>
> +
> +#define VIRTIO_PSTORE_CMD_NULL   0
> +#define VIRTIO_PSTORE_CMD_OPEN   1
> +#define VIRTIO_PSTORE_CMD_READ   2
> +#define VIRTIO_PSTORE_CMD_WRITE  3
> +#define VIRTIO_PSTORE_CMD_ERASE  4
> +#define VIRTIO_PSTORE_CMD_CLOSE  5
> +
> +#define VIRTIO_PSTORE_TYPE_UNKNOWN  0
> +#define VIRTIO_PSTORE_TYPE_DMESG    1
> +
> +#define VIRTIO_PSTORE_FL_COMPRESSED  1

Most other headers use _F_ and not _FL_
Also, we specify bit number and not the
bitmask. So:

#define VIRTIO_PSTORE_F_COMPRESSED  0

and

(0x1 << VIRTIO_PSTORE_F_COMPRESSED)


> +
> +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;
> +};
> +
> +struct virtio_pstore_fileinfo {
> +     __virtio64              id;
> +     __virtio32              count;
> +     __virtio16              type;
> +     __virtio16              unused;
> +     __virtio32              flags;
> +     __virtio32              len;
> +     __virtio64              time_sec;
> +     __virtio32              time_nsec;
> +     __virtio32              reserved;

Any reason one is reserved the other is unused?
If not just calls them pad1, pad2?

> +};
> +
> +struct virtio_pstore_config {
> +     __virtio32              bufsize;
> +};
> +

__virtio things are for compatibility things.
New devices should just use __le everywhere.

Let me post a patch that adds config space accessors
so you can do this.


> +#endif /* _LINUX_VIRTIO_PSTORE_H */
> -- 
> 2.9.3



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