Re: [Qemu-devel] [PATCH 3/3] dataplane: handle misaligned virtio-blk requests

[Paolo Bonzini]

Il 11/01/2013 13:39, Kevin Wolf ha scritto:
> Am 10.01.2013 17:48, schrieb Stefan Hajnoczi:
>> O_DIRECT on Linux has alignment requirements on I/O buffers and
>> misaligned requests result in -EINVAL.  The Linux virtio_blk guest
>> driver usually submits aligned requests so I forgot to handle misaligned
>> requests.
>>
>> It turns out that virtio-win guest drivers submit misaligned requests.
>> Handle them using a bounce buffer that meets alignment requirements.
>>
>> Signed-off-by: Stefan Hajnoczi <address@hidden>
>> ---
>>  hw/dataplane/virtio-blk.c | 36 ++++++++++++++++++++++++++++++++++++
>>  1 file changed, 36 insertions(+)
>>
>> diff --git a/hw/dataplane/virtio-blk.c b/hw/dataplane/virtio-blk.c
>> index a6696b8..991ab5f 100644
>> --- a/hw/dataplane/virtio-blk.c
>> +++ b/hw/dataplane/virtio-blk.c
>> @@ -34,6 +34,8 @@ typedef struct {
>>      struct iocb iocb;               /* Linux AIO control block */
>>      QEMUIOVector *inhdr;            /* iovecs for virtio_blk_inhdr */
>>      unsigned int head;              /* vring descriptor index */
>> +    void *bounce_buffer;            /* used if guest buffers are unaligned 
>> */
>> +    QEMUIOVector *read_qiov;        /* for read completion /w bounce buffer 
>> */
>>  } VirtIOBlockRequest;
>>  
>>  struct VirtIOBlockDataPlane {
>> @@ -89,6 +91,15 @@ static void complete_request(struct iocb *iocb, ssize_t 
>> ret, void *opaque)
>>  
>>      trace_virtio_blk_data_plane_complete_request(s, req->head, ret);
>>  
>> +    if (req->read_qiov) {
>> +        assert(req->bounce_buffer);
>> +        qemu_iovec_to_buf(req->read_qiov, 0, req->bounce_buffer, len);
> 
> Shouldn't it be qemu_iovec_from_buf()?

Yes.

> Makes me wonder if qtest cases might be doable...

Anthony, what's going on with libqos? :)

In the meanwhile...

>> +        qemu_iovec_destroy(req->read_qiov);
>> +        g_slice_free(QEMUIOVector, req->read_qiov);
>> +    }
>> +
>> +    qemu_vfree(req->bounce_buffer);
>> +
>>      qemu_iovec_from_buf(req->inhdr, 0, &hdr, sizeof(hdr));
>>      qemu_iovec_destroy(req->inhdr);
>>      g_slice_free(QEMUIOVector, req->inhdr);
>> @@ -136,6 +147,29 @@ static int do_rdwr_cmd(VirtIOBlockDataPlane *s, bool 
>> read,
>>                         QEMUIOVector *inhdr)
>>  {
>>      struct iocb *iocb;
>> +    QEMUIOVector qiov;
>> +    struct iovec bounce_iov;
>> +    void *bounce_buffer = NULL;
>> +    QEMUIOVector *read_qiov = NULL;
>> +
>> +    qemu_iovec_init_external(&qiov, iov, iov_cnt);
>> +    if (!bdrv_qiov_is_aligned(s->blk->conf.bs, &qiov)) {

... changing this to "if (1)" would be enough for testing with Linux guests.

Paolo

>> +        /* Redirect I/O to aligned bounce buffer */
>> +        bounce_buffer = qemu_blockalign(s->blk->conf.bs, qiov.size);
>> +        bounce_iov.iov_base = bounce_buffer;
>> +        bounce_iov.iov_len = qiov.size;
>> +        iov = &bounce_iov;
>> +        iov_cnt = 1;
>> +
>> +        if (read) {
>> +            /* Need to copy back from bounce buffer on completion */
>> +            read_qiov = g_slice_new(QEMUIOVector);
>> +            qemu_iovec_init(read_qiov, iov_cnt);
>> +            qemu_iovec_concat_iov(read_qiov, iov, iov_cnt, 0, qiov.size);
> 
> This would have to be the original iov and iov_cnt, but they are already
> overwritten here.
> 
>> +        } else {
>> +            qemu_iovec_to_buf(&qiov, 0, bounce_buffer, qiov.size);
>> +        }
>> +    }
>>  
>>      iocb = ioq_rdwr(&s->ioqueue, read, iov, iov_cnt, offset);
>>  
>> @@ -143,6 +177,8 @@ static int do_rdwr_cmd(VirtIOBlockDataPlane *s, bool 
>> read,
>>      VirtIOBlockRequest *req = container_of(iocb, VirtIOBlockRequest, iocb);
>>      req->head = head;
>>      req->inhdr = inhdr;
>> +    req->bounce_buffer = bounce_buffer;
>> +    req->read_qiov = read_qiov;
>>      return 0;
>>  }
> 
> Kevin
> 
>