Re: [Qemu-devel] [PATCH 09/10] posix-aio-compat: Allow read after EOF

[Frediano Ziglio]

2011/7/26 Kevin Wolf <address@hidden>:
> In order to be able to transparently replace bdrv_read calls by bdrv_co_read,
> reading beyond EOF must produce zeros instead of short reads for AIO, too.
>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  posix-aio-compat.c |   19 +++++++++++++++++++
>  1 files changed, 19 insertions(+), 0 deletions(-)
>
> diff --git a/posix-aio-compat.c b/posix-aio-compat.c
> index 788d113..8dc00cb 100644
> --- a/posix-aio-compat.c
> +++ b/posix-aio-compat.c
> @@ -198,6 +198,12 @@ static ssize_t handle_aiocb_rw_vector(struct qemu_paiocb 
> *aiocb)
>     return len;
>  }
>
> +/*
> + * Read/writes the data to/from a given linear buffer.
> + *
> + * Returns the number of bytes handles or -errno in case of an error. Short
> + * reads are only returned if the end of the file is reached.
> + */
>  static ssize_t handle_aiocb_rw_linear(struct qemu_paiocb *aiocb, char *buf)
>  {
>     ssize_t offset = 0;
> @@ -334,6 +340,19 @@ static void *aio_thread(void *unused)
>
>         switch (aiocb->aio_type & QEMU_AIO_TYPE_MASK) {
>         case QEMU_AIO_READ:
> +            ret = handle_aiocb_rw(aiocb);
> +            if (ret >= 0 && ret < aiocb->aio_nbytes && 
> aiocb->common.bs->growable) {
> +                /* A short read means that we have reached EOF. Pad the 
> buffer
> +                 * with zeros for bytes after EOF. */
> +                QEMUIOVector qiov;
> +
> +                qemu_iovec_init_external(&qiov, aiocb->aio_iov,
> +                                         aiocb->aio_niov);
> +                qemu_iovec_memset_skip(&qiov, 0, aiocb->aio_nbytes - ret, 
> ret);
> +
> +                ret = aiocb->aio_nbytes;
> +            }
> +            break;
>         case QEMU_AIO_WRITE:
>             ret = handle_aiocb_rw(aiocb);
>             break;
> --
> 1.7.6
>

Still not tested but I think to know what does it solve :)

I think Linux AIO require same attention.

Frediano