Re: [Qemu-devel] [PATCH 1/2] qemu-img: async write to block device when converting image

[Sage Weil <sage@newdream.net>]

On Wed, 7 Sep 2011, Yehuda Sadeh wrote:
> In order to improve image conversion process, instead of synchronously
> writing the destingation image, we keep a window of async writes.
> 
> Signed-off-by: Yehuda Sadeh <yehuda@hq.newdream.net>

Small fix below:

> ---
>  qemu-img.c |   28 +++++++++++++++++++++++-----
>  1 files changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/qemu-img.c b/qemu-img.c
> index b205e98..0552746 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -622,6 +622,17 @@ static int compare_sectors(const uint8_t *buf1, const uint8_t *buf2, int n,
>  }
>  
>  #define IO_BUF_SIZE (2 * 1024 * 1024)
> +#define IO_WRITE_WINDOW_THRESHOLD (32 * 1024 * 1024)
> +
> +static int write_window = 0;
> +
> +static void img_write_cb(void *opaque, int ret)
> +{
> +    QEMUIOVector *qiov = (QEMUIOVector *)opaque;
> +    write_window -=  qiov->iov->iov_len / 512;
> +    qemu_iovec_destroy(qiov);    
> +    qemu_free(qiov);
> +}
>  
>  static int img_convert(int argc, char **argv)
>  {
> @@ -980,6 +991,9 @@ static int img_convert(int argc, char **argv)
>                 should add a specific call to have the info to go faster */
>              buf1 = buf;
>              while (n > 0) {
> +                while (write_window > IO_WRITE_WINDOW_THRESHOLD / 512) {
> +                    qemu_aio_wait();
> +                }
>                  /* If the output image is being created as a copy on write image,
>                     copy all sectors even the ones containing only NUL bytes,
>                     because they may differ from the sectors in the base image.
> @@ -989,11 +1003,11 @@ static int img_convert(int argc, char **argv)
>                     already there is garbage, not 0s. */
>                  if (!has_zero_init || out_baseimg ||
>                      is_allocated_sectors(buf1, n, &n1)) {
> -                    ret = bdrv_write(out_bs, sector_num, buf1, n1);
> -                    if (ret < 0) {
> -                        error_report("error while writing");
> -                        goto out;
> -                    }
> +                    QEMUIOVector *qiov = qemu_mallocz(sizeof(QEMUIOVector));
> +		    qemu_iovec_init(qiov, 1);
> +		    qemu_iovec_add(qiov, (void *)buf1, n1 * 512);
> +                    bdrv_aio_writev(out_bs, sector_num, qiov, n1, img_write_cb, qiov);
> +                    write_window += n1;
>                  }
>                  sector_num += n1;
>                  n -= n1;
> @@ -1001,11 +1015,15 @@ static int img_convert(int argc, char **argv)
>              }
>              qemu_progress_print(local_progress, 100);
>          }
> +        while (write_window > 0) {
> +            qemu_aio_wait();
> +        }
>      }
>  out:
>      qemu_progress_end();
>      free_option_parameters(create_options);
>      free_option_parameters(param);
> +    bdrv_flush(out_bs);
>      qemu_free(buf);
>      if (out_bs) {
>          bdrv_delete(out_bs);

The bdrv_flush() needs to go inside the if or else we get a null 
dereference on error (e.g. from a bad image name).

sage


> -- 
> 1.7.5.1
> 
> 
>