[Qemu-devel] [PATCH v3] block: document semanatics of bdrv_co_preadv|pwritev

[Qemu-devel] [PATCH v3] block: document semanatics of bdrv_co_preadv|pwritev

[Daniel P. Berrange]

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---

 - Clarify that @bytes matches @qiov total size (Kevin)

 include/block/block_int.h | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index d4f4ea7584..4f7f20e56b 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -147,12 +147,43 @@ struct BlockDriver {
 
     int coroutine_fn (*bdrv_co_readv)(BlockDriverState *bs,
         int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
+
+    /**
+     * @offset: position in bytes to read at
+     * @bytes: number of bytes to read
+     * @qiov: the buffers to fill with read data
+     * @flags: currently unused, always 0
+     *
+     * @offset and @bytes will be a multiple of 'request_alignment',
+     * but the length of individual @qiov elements does not have to
+     * be a multiple.
+     *
+     * @bytes will always equal the total size of @qiov, and will be
+     * no larger than 'max_transfer'.
+     *
+     * The buffer in @qiov may point directly to guest memory.
+     */
     int coroutine_fn (*bdrv_co_preadv)(BlockDriverState *bs,
         uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags);
     int coroutine_fn (*bdrv_co_writev)(BlockDriverState *bs,
         int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
     int coroutine_fn (*bdrv_co_writev_flags)(BlockDriverState *bs,
         int64_t sector_num, int nb_sectors, QEMUIOVector *qiov, int flags);
+    /**
+     * @offset: position in bytes to write at
+     * @bytes: number of bytes to write
+     * @qiov: the buffers containing data to write
+     * @flags: zero or more of bits allowed by 'supported_write_flags'
+     *
+     * @offset and @bytes will be a multiple of 'request_alignment',
+     * but the length of individual @qiov elements does not have to
+     * be a multiple.
+     *
+     * @bytes will always equal the total size of @qiov, and will be
+     * no larger than 'max_transfer'.
+     *
+     * The buffer in @qiov may point directly to guest memory.
+     */
     int coroutine_fn (*bdrv_co_pwritev)(BlockDriverState *bs,
         uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags);
 
-- 
2.13.3

Re: [Qemu-devel] [PATCH v3] block: document semanatics of bdrv_co_preadv|pwritev

[Eric Blake]

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On 08/04/2017 09:08 AM, Daniel P. Berrange wrote:
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
> 
>  - Clarify that @bytes matches @qiov total size (Kevin)
> 
>  include/block/block_int.h | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)

[looks like the nongnu.org infrastructure is having heavy load today, so
mails are getting through more slowly than usual - leads to lots of
crossed emails, where I'm seeing replies or direct sends sooner than
list copies]

> +    /**
> +     * @offset: position in bytes to write at
> +     * @bytes: number of bytes to write
> +     * @qiov: the buffers containing data to write
> +     * @flags: zero or more of bits allowed by 'supported_write_flags'

maybe s/of //

> +     *
> +     * @offset and @bytes will be a multiple of 'request_alignment',
> +     * but the length of individual @qiov elements does not have to
> +     * be a multiple.
> +     *
> +     * @bytes will always equal the total size of @qiov, and will be
> +     * no larger than 'max_transfer'.
> +     *
> +     * The buffer in @qiov may point directly to guest memory.
> +     */
>      int coroutine_fn (*bdrv_co_pwritev)(BlockDriverState *bs,
>          uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags);

Do we make guarantees that the driver callback is never reached if the
image is currently read-only?  If so, is that a guarantee worth documenting?

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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Re: [Qemu-devel] [PATCH v3] block: document semanatics of bdrv_co_preadv|pwritev

[Daniel P. Berrange]

On Fri, Aug 04, 2017 at 09:28:54AM -0500, Eric Blake wrote:
> On 08/04/2017 09:08 AM, Daniel P. Berrange wrote:
> > Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> > ---
> > 
> >  - Clarify that @bytes matches @qiov total size (Kevin)
> > 
> >  include/block/block_int.h | 31 +++++++++++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> 
> [looks like the nongnu.org infrastructure is having heavy load today, so
> mails are getting through more slowly than usual - leads to lots of
> crossed emails, where I'm seeing replies or direct sends sooner than
> list copies]
> 
> > +    /**
> > +     * @offset: position in bytes to write at
> > +     * @bytes: number of bytes to write
> > +     * @qiov: the buffers containing data to write
> > +     * @flags: zero or more of bits allowed by 'supported_write_flags'
> 
> maybe s/of //
> 
> > +     *
> > +     * @offset and @bytes will be a multiple of 'request_alignment',
> > +     * but the length of individual @qiov elements does not have to
> > +     * be a multiple.
> > +     *
> > +     * @bytes will always equal the total size of @qiov, and will be
> > +     * no larger than 'max_transfer'.
> > +     *
> > +     * The buffer in @qiov may point directly to guest memory.
> > +     */
> >      int coroutine_fn (*bdrv_co_pwritev)(BlockDriverState *bs,
> >          uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags);
> 
> Do we make guarantees that the driver callback is never reached if the
> image is currently read-only?  If so, is that a guarantee worth documenting?

bdrv_co_pwritev() returns EPERM if bs->read_only, so it looks like you
are right we have a guarantee we can document

> Reviewed-by: Eric Blake <eblake@redhat.com>


Regards,
Daniel
-- 
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Re: [Qemu-devel] [Qemu-block] [PATCH v3] block: document semanatics of bdrv_co_preadv|pwritev

[Stefan Hajnoczi]

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On Fri, Aug 04, 2017 at 03:08:26PM +0100, Daniel P. Berrange wrote:
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
> 
>  - Clarify that @bytes matches @qiov total size (Kevin)
> 
>  include/block/block_int.h | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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