Re: [Qemu-devel] [PATCH v2] virtio-blk: set correct config size for the host driver
> -Original Message-
> From: Michael S. Tsirkin [mailto:m...@redhat.com]
> Sent: Tuesday, February 12, 2019 9:49 PM
> To: Liu, Changpeng
> Cc: qemu-devel@nongnu.org; stefa...@redhat.com; sgarz...@redhat.com;
> dgilb...@redhat.com; ldok...@redhat.com
> Subject: Re: [PATCH v2] virtio-blk: set correct config size for the host
> driver
>
> On Tue, Feb 12, 2019 at 02:01:44PM +0800, Changpeng Liu wrote:
> > Commit caa1ee43 "vhost-user-blk: add discard/write zeroes features support"
> > introduced extra fields to existing struct virtio_blk_config, when
> > migration was executed from older QEMU version to current head, it
> > will break the migration. While here, set the correct config size
> > when initializing the host driver, for now, discard/write zeroes
> > are not supported by virtio-blk host driver, so set the config
> > size as before, users can change config size when adding the new
> > feature bits support.
> >
> > Signed-off-by: Changpeng Liu
>
>
> Pls rewrite commit log as suggested in this thread
> and repost.
Thanks, repost a v3 patch to address the commit message and your following
comments.
>
> > ---
> > hw/block/virtio-blk.c | 10 ++
> > 1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> > index 9a87b3b..846b7b9 100644
> > --- a/hw/block/virtio-blk.c
> > +++ b/hw/block/virtio-blk.c
> > @@ -28,6 +28,9 @@
> > #include "hw/virtio/virtio-bus.h"
> > #include "hw/virtio/virtio-access.h"
> >
> > +#define VIRTIO_BLK_CFG_SIZE (offsetof(struct virtio_blk_config, num_queues)
> + \
> > + sizeof_field(struct virtio_blk_config,
> > num_queues))
> > +
>
> I would just do offsetof(max_discard_sectors)
> with a comment "we don't support discard yet, hide associated config
> fields".
>
> > static void virtio_blk_init_request(VirtIOBlock *s, VirtQueue *vq,
> > VirtIOBlockReq *req)
> > {
> > @@ -761,7 +764,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev,
> uint8_t *config)
> > blkcfg.alignment_offset = 0;
> > blkcfg.wce = blk_enable_write_cache(s->blk);
> > virtio_stw_p(vdev, _queues, s->conf.num_queues);
> > -memcpy(config, , sizeof(struct virtio_blk_config));
> > +memcpy(config, , VIRTIO_BLK_CFG_SIZE);
>
>
> Let's add QEMU_BUILD_BUG_ON(VIRTIO_BLK_CFG_SIZE <= sizeof(struct
> virtio_blk_config)) just for documentation purposes.
>
> > }
> >
> > static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t
> > *config)
> > @@ -769,7 +772,7 @@ static void virtio_blk_set_config(VirtIODevice *vdev,
> const uint8_t *config)
> > VirtIOBlock *s = VIRTIO_BLK(vdev);
> > struct virtio_blk_config blkcfg;
> >
> > -memcpy(, config, sizeof(blkcfg));
> > +memcpy(, config, VIRTIO_BLK_CFG_SIZE);
>
>
> Here too, QEMU_BUILD_BUG_ON(VIRTIO_BLK_CFG_SIZE <= sizeof(blkcfg))
>
> >
> > aio_context_acquire(blk_get_aio_context(s->blk));
> > blk_set_enable_write_cache(s->blk, blkcfg.wce != 0);
> > @@ -952,8 +955,7 @@ static void virtio_blk_device_realize(DeviceState *dev,
> Error **errp)
> > return;
> > }
> >
> > -virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK,
> > -sizeof(struct virtio_blk_config));
> > +virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK, VIRTIO_BLK_CFG_SIZE);
> >
> > s->blk = conf->conf.blk;
> > s->rq = NULL;
> > --
> > 1.9.3
Re: [Qemu-devel] [PATCH v2] virtio-blk: set correct config size for the host driver
On Tue, Feb 12, 2019 at 02:01:44PM +0800, Changpeng Liu wrote:
> Commit caa1ee43 "vhost-user-blk: add discard/write zeroes features support"
> introduced extra fields to existing struct virtio_blk_config, when
> migration was executed from older QEMU version to current head, it
> will break the migration. While here, set the correct config size
> when initializing the host driver, for now, discard/write zeroes
> are not supported by virtio-blk host driver, so set the config
> size as before, users can change config size when adding the new
> feature bits support.
>
> Signed-off-by: Changpeng Liu
Pls rewrite commit log as suggested in this thread
and repost.
> ---
> hw/block/virtio-blk.c | 10 ++
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 9a87b3b..846b7b9 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -28,6 +28,9 @@
> #include "hw/virtio/virtio-bus.h"
> #include "hw/virtio/virtio-access.h"
>
> +#define VIRTIO_BLK_CFG_SIZE (offsetof(struct virtio_blk_config, num_queues)
> + \
> + sizeof_field(struct virtio_blk_config,
> num_queues))
> +
I would just do offsetof(max_discard_sectors)
with a comment "we don't support discard yet, hide associated config
fields".
> static void virtio_blk_init_request(VirtIOBlock *s, VirtQueue *vq,
> VirtIOBlockReq *req)
> {
> @@ -761,7 +764,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev,
> uint8_t *config)
> blkcfg.alignment_offset = 0;
> blkcfg.wce = blk_enable_write_cache(s->blk);
> virtio_stw_p(vdev, _queues, s->conf.num_queues);
> -memcpy(config, , sizeof(struct virtio_blk_config));
> +memcpy(config, , VIRTIO_BLK_CFG_SIZE);
Let's add QEMU_BUILD_BUG_ON(VIRTIO_BLK_CFG_SIZE <= sizeof(struct
virtio_blk_config)) just for documentation purposes.
> }
>
> static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
> @@ -769,7 +772,7 @@ static void virtio_blk_set_config(VirtIODevice *vdev,
> const uint8_t *config)
> VirtIOBlock *s = VIRTIO_BLK(vdev);
> struct virtio_blk_config blkcfg;
>
> -memcpy(, config, sizeof(blkcfg));
> +memcpy(, config, VIRTIO_BLK_CFG_SIZE);
Here too, QEMU_BUILD_BUG_ON(VIRTIO_BLK_CFG_SIZE <= sizeof(blkcfg))
>
> aio_context_acquire(blk_get_aio_context(s->blk));
> blk_set_enable_write_cache(s->blk, blkcfg.wce != 0);
> @@ -952,8 +955,7 @@ static void virtio_blk_device_realize(DeviceState *dev,
> Error **errp)
> return;
> }
>
> -virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK,
> -sizeof(struct virtio_blk_config));
> +virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK, VIRTIO_BLK_CFG_SIZE);
>
> s->blk = conf->conf.blk;
> s->rq = NULL;
> --
> 1.9.3
Re: [Qemu-devel] [PATCH v2] virtio-blk: set correct config size for the host driver
On Tue, 12 Feb 2019 14:01:44 +0800
Changpeng Liu wrote:
> Commit caa1ee43 "vhost-user-blk: add discard/write zeroes features support"
> introduced extra fields to existing struct virtio_blk_config, when
> migration was executed from older QEMU version to current head, it
A hint about the breakage is often a good practice, as it helps
people to find the fix if they hit the issue.
> will break the migration. While here, set the correct config size
"While here" usually means that the corresponding change isn't strictly
needed. I don't believe this is the case here since fixing the config
size is precisely the goal of this patch.
> when initializing the host driver, for now, discard/write zeroes
> are not supported by virtio-blk host driver, so set the config
As mentioned by Michael, there's no such thing as a "host driver".
Just say virtio-blk.
> size as before, users can change config size when adding the new
> feature bits support.
>
What about ?
Commit caa1ee43 "vhost-user-blk: add discard/write zeroes features
support" added fields to struct virtio_blk_config. This changes
the size of the config space and breaks migration from QEMU 3.1
and older:
qemu-system-ppc64: get_pci_config_device: Bad config data: i=0x10 read: 41
device: 1 cmask: ff wmask: 80 w1cmask:0
qemu-system-ppc64: Failed to load PCIDevice:config
qemu-system-ppc64: Failed to load virtio-blk:virtio
qemu-system-ppc64: error while loading state for instance 0x0 of device
'pci@8002000:01.0/virtio-blk'
qemu-system-ppc64: load of migration failed: Invalid argument
Since virtio-blk doesn't support the "discard" and "write zeroes"
features, it shouldn't even expose the associated fields in the
config space actually. Just include all fields up to num_queues to
match QEMU 3.1 and older.
> Signed-off-by: Changpeng Liu
> ---
LGTM
Reviewed-by: Greg Kurz
Tested-by: Greg Kurz
> hw/block/virtio-blk.c | 10 ++
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 9a87b3b..846b7b9 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -28,6 +28,9 @@
> #include "hw/virtio/virtio-bus.h"
> #include "hw/virtio/virtio-access.h"
>
> +#define VIRTIO_BLK_CFG_SIZE (offsetof(struct virtio_blk_config, num_queues)
> + \
> + sizeof_field(struct virtio_blk_config,
> num_queues))
> +
> static void virtio_blk_init_request(VirtIOBlock *s, VirtQueue *vq,
> VirtIOBlockReq *req)
> {
> @@ -761,7 +764,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev,
> uint8_t *config)
> blkcfg.alignment_offset = 0;
> blkcfg.wce = blk_enable_write_cache(s->blk);
> virtio_stw_p(vdev, _queues, s->conf.num_queues);
> -memcpy(config, , sizeof(struct virtio_blk_config));
> +memcpy(config, , VIRTIO_BLK_CFG_SIZE);
> }
>
> static void virtio_blk_set_config(VirtIODevice *vdev, const uint8_t *config)
> @@ -769,7 +772,7 @@ static void virtio_blk_set_config(VirtIODevice *vdev,
> const uint8_t *config)
> VirtIOBlock *s = VIRTIO_BLK(vdev);
> struct virtio_blk_config blkcfg;
>
> -memcpy(, config, sizeof(blkcfg));
> +memcpy(, config, VIRTIO_BLK_CFG_SIZE);
>
> aio_context_acquire(blk_get_aio_context(s->blk));
> blk_set_enable_write_cache(s->blk, blkcfg.wce != 0);
> @@ -952,8 +955,7 @@ static void virtio_blk_device_realize(DeviceState *dev,
> Error **errp)
> return;
> }
>
> -virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK,
> -sizeof(struct virtio_blk_config));
> +virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK, VIRTIO_BLK_CFG_SIZE);
>
> s->blk = conf->conf.blk;
> s->rq = NULL;
