Re: [Qemu-devel] [STABLE][PATCH 4/4] Fix DMA API when handling an immediate error from block layer

[Mark McLoughlin <markmc@redhat.com>]

On Thu, 2009-05-14 at 11:56 +0100, Mark McLoughlin wrote:
> From: Avi Kivity <avi@redhat.com>
> 
> The block layer may signal an immediate error on an asynchronous request
> by returning NULL.  The DMA API did not handle this correctly, returning
> an AIO request which would never complete (and which would crash if
> cancelled).
> 
> Fix by detecting the failure and propagating it.
> 
> Signed-off-by: Avi Kivity <avi@redhat.com>

Signed-off-by: Mark McLoughlin <markmc@redhat.com>

> ---
>  dma-helpers.c |   27 +++++++++++++++++++++------
>  1 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/dma-helpers.c b/dma-helpers.c
> index 96a120c..1469e34 100644
> --- a/dma-helpers.c
> +++ b/dma-helpers.c
> @@ -70,20 +70,26 @@ static void continue_after_map_failure(void *opaque)
>      qemu_bh_schedule(dbs->bh);
>  }
>  
> -static void dma_bdrv_cb(void *opaque, int ret)
> +static void dma_bdrv_unmap(DMAAIOCB *dbs)
>  {
> -    DMAAIOCB *dbs = (DMAAIOCB *)opaque;
> -    target_phys_addr_t cur_addr, cur_len;
> -    void *mem;
>      int i;
>  
> -    dbs->acb = NULL;
> -    dbs->sector_num += dbs->iov.size / 512;
>      for (i = 0; i < dbs->iov.niov; ++i) {
>          cpu_physical_memory_unmap(dbs->iov.iov[i].iov_base,
>                                    dbs->iov.iov[i].iov_len, !dbs->is_write,
>                                    dbs->iov.iov[i].iov_len);
>      }
> +}
> +
> +void dma_bdrv_cb(void *opaque, int ret)
> +{
> +    DMAAIOCB *dbs = (DMAAIOCB *)opaque;
> +    target_phys_addr_t cur_addr, cur_len;
> +    void *mem;
> +
> +    dbs->acb = NULL;
> +    dbs->sector_num += dbs->iov.size / 512;
> +    dma_bdrv_unmap(dbs);
>      qemu_iovec_reset(&dbs->iov);
>  
>      if (dbs->sg_cur_index == dbs->sg->nsg || ret < 0) {
> @@ -119,6 +125,11 @@ static void dma_bdrv_cb(void *opaque, int ret)
>          dbs->acb = bdrv_aio_readv(dbs->bs, dbs->sector_num, &dbs->iov,
>                                    dbs->iov.size / 512, dma_bdrv_cb, dbs);
>      }
> +    if (!dbs->acb) {
> +        dma_bdrv_unmap(dbs);
> +        qemu_iovec_destroy(&dbs->iov);
> +        return;
> +    }
>  }
>  
>  static BlockDriverAIOCB *dma_bdrv_io(
> @@ -138,6 +149,10 @@ static BlockDriverAIOCB *dma_bdrv_io(
>      dbs->bh = NULL;
>      qemu_iovec_init(&dbs->iov, sg->nsg);
>      dma_bdrv_cb(dbs, 0);
> +    if (!dbs->acb) {
> +        qemu_aio_release(dbs);
> +        return NULL;
> +    }
>      return &dbs->common;
>  }
>