Re: [Qemu-devel] [PATCH] block: fix big write

[Max Reitz <mreitz@redhat.com>]

On 2014-12-05 at 17:15, Ming Lei wrote:
> From: Ming Lei <ming.lei@caonical.com>
>
> QEMU block should have supported to read/write at most
> 0x7fffff * 512 bytes, unfortunately INT_MAX is used to check
> bytes in both bdrv_co_do_writev() and bdrv_check_byte_request(),
> so cause write failure if nr_sectors is equal or more
> than 0x400000.
>
> There are still other INT_MAX usages in block.c, and they might
> need to change to UINT_MAX too in future, but at least
> this patch's change can make SCSI WRITE SAME 16 workable.
>
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Ming Lei <ming.lei@caonical.com>
> ---
>   block.c |    4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/block.c b/block.c
> index a612594..ddc18c2 100644
> --- a/block.c
> +++ b/block.c
> @@ -2607,7 +2607,7 @@ static int bdrv_check_byte_request(BlockDriverState *bs, int64_t offset,
>   {
>       int64_t len;
>   
> -    if (size > INT_MAX) {
> +    if (size > UINT_MAX) {
>           return -EIO;
>       }
>   
> @@ -3420,7 +3420,7 @@ static int coroutine_fn bdrv_co_do_writev(BlockDriverState *bs,
>       int64_t sector_num, int nb_sectors, QEMUIOVector *qiov,
>       BdrvRequestFlags flags)
>   {
> -    if (nb_sectors < 0 || nb_sectors > (INT_MAX >> BDRV_SECTOR_BITS)) {
> +    if (nb_sectors < 0 || nb_sectors > (UINT_MAX >> BDRV_SECTOR_BITS)) {
>           return -EINVAL;
>       }
>   

This is intentional so a byte length can be stored in an integer. This 
is a pretty bad design decision, but we have to live with it until we 
really fix the block layer regarding the type lengths are stored in.

Max