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

[Paolo Bonzini <pbonzini@redhat.com>]

On 05/12/2014 18:03, Max Reitz wrote:
> 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.

No problem, let's fix SCSI (the correct way, which is not the patch
posted so far :)).

Paolo