Re: [Qemu-devel] [PATCH v2] block: avoid creating too large iovecs in multiwrite_merge

[Anthony Liguori <anthony@codemonkey.ws>]

On 01/26/2010 07:49 AM, Christoph Hellwig wrote:
> If we go over the maximum number of iovecs support by syscall we get
> back EINVAL from the kernel which translate to I/O errors for the guest.
>
> Add a MAX_IOV defintion for platforms that don't have it.  For now we use
> the same 1024 define that's used on Linux and various other platforms,
> but until the windows block backend implements some kind of vectored I/O
> it doesn't matter.
>
> Signed-off-by: Christoph Hellwig<hch@lst.de>
>    

Applied.  Thanks.

Regards,

Anthony Liguori
> Index: qemu/block.c
> ===================================================================
> --- qemu.orig/block.c	2010-01-26 10:59:39.757004445 +0100
> +++ qemu/block.c	2010-01-26 11:01:38.056023231 +0100
> @@ -1689,6 +1689,10 @@ static int multiwrite_merge(BlockDriverS
>               merge = bs->drv->bdrv_merge_requests(bs,&reqs[outidx],&reqs[i]);
>           }
>
> +        if (reqs[outidx].qiov->niov + reqs[i].qiov->niov + 1>  IOV_MAX) {
> +            merge = 0;
> +        }
> +
>           if (merge) {
>               size_t size;
>               QEMUIOVector *qiov = qemu_mallocz(sizeof(*qiov));
> Index: qemu/qemu-common.h
> ===================================================================
> --- qemu.orig/qemu-common.h	2010-01-26 14:41:40.894254285 +0100
> +++ qemu/qemu-common.h	2010-01-26 14:42:27.267275698 +0100
> @@ -54,6 +54,10 @@ struct iovec {
>       void *iov_base;
>       size_t iov_len;
>   };
> +/*
> + * Use the same value as Linux for now.
> + */
> +#define IOV_MAX		1024
>   #else
>   #include<sys/uio.h>
>   #endif
>
>
>
>