Re: [Qemu-devel] [PATCH] block: introduce BDRV_REQUEST_MAX_SECTORS

[Peter Lieven <pl@kamp.de>]

Am 03.02.2015 um 14:29 schrieb Denis V. Lunev:
> On 03/02/15 15:12, Peter Lieven wrote:
>> we check and adjust request sizes at several places with
>> sometimes inconsistent checks or default values:
>>   INT_MAX
>>   INT_MAX >> BDRV_SECTOR_BITS
>>   UINT_MAX >> BDRV_SECTOR_BITS
>>   SIZE_MAX >> BDRV_SECTOR_BITS
>>
>> This patches introdocues a macro for the maximal allowed sectors
>> per request and uses it at several places.
>>
>> Signed-off-by: Peter Lieven <pl@kamp.de>
>> ---
>>   block.c               | 19 ++++++++-----------
>>   hw/block/virtio-blk.c |  4 ++--
>>   include/block/block.h |  3 +++
>>   3 files changed, 13 insertions(+), 13 deletions(-)
>>
>> diff --git a/block.c b/block.c
>> index 8272ef9..4e58b35 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -2671,7 +2671,7 @@ static int bdrv_check_byte_request(BlockDriverState *bs, int64_t offset,
>>   static int bdrv_check_request(BlockDriverState *bs, int64_t sector_num,
>>                                 int nb_sectors)
>>   {
>> -    if (nb_sectors < 0 || nb_sectors > INT_MAX / BDRV_SECTOR_SIZE) {
>> +    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
>>           return -EIO;
>>       }
>>   @@ -2758,7 +2758,7 @@ static int bdrv_rw_co(BlockDriverState *bs, int64_t sector_num, uint8_t *buf,
>>           .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
>>       };
>>   -    if (nb_sectors < 0 || nb_sectors > INT_MAX / BDRV_SECTOR_SIZE) {
>> +    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
>>           return -EINVAL;
>>       }
>>   @@ -2826,13 +2826,10 @@ int bdrv_make_zero(BlockDriverState *bs, BdrvRequestFlags flags)
>>       }
>>         for (;;) {
>> -        nb_sectors = target_sectors - sector_num;
>> +        nb_sectors = MIN(target_sectors - sector_num, BDRV_REQUEST_MAX_SECTORS);
>>           if (nb_sectors <= 0) {
>>               return 0;
>>           }
>> -        if (nb_sectors > INT_MAX / BDRV_SECTOR_SIZE) {
>> -            nb_sectors = INT_MAX / BDRV_SECTOR_SIZE;
>> -        }
>>           ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &n);
>>           if (ret < 0) {
>>               error_report("error getting block status at sector %" PRId64 ": %s",
>> @@ -3167,7 +3164,7 @@ static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
>>       int64_t sector_num, int nb_sectors, QEMUIOVector *qiov,
>>       BdrvRequestFlags flags)
>>   {
>> -    if (nb_sectors < 0 || nb_sectors > (UINT_MAX >> BDRV_SECTOR_BITS)) {
>> +    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
>>           return -EINVAL;
>>       }
>>   @@ -3202,8 +3199,8 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
>>       struct iovec iov = {0};
>>       int ret = 0;
>>   -    int max_write_zeroes = bs->bl.max_write_zeroes ?
>> -                           bs->bl.max_write_zeroes : INT_MAX;
>> +    int max_write_zeroes = MIN_NON_ZERO(bs->bl.max_write_zeroes,
>> + BDRV_REQUEST_MAX_SECTORS);
>>         while (nb_sectors > 0 && !ret) {
>>           int num = nb_sectors;
>> @@ -3458,7 +3455,7 @@ 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 > BDRV_REQUEST_MAX_SECTORS) {
>>           return -EINVAL;
>>       }
>>   @@ -5120,7 +5117,7 @@ int coroutine_fn bdrv_co_discard(BlockDriverState *bs, int64_t sector_num,
>>           return 0;
>>       }
>>   -    max_discard = bs->bl.max_discard ? bs->bl.max_discard : INT_MAX;
>> +    max_discard = MIN_NON_ZERO(bs->bl.max_discard, BDRV_REQUEST_MAX_SECTORS);
>>       while (nb_sectors > 0) {
>>           int ret;
>>           int num = nb_sectors;
>> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
>> index 8c51a29..1a8a176 100644
>> --- a/hw/block/virtio-blk.c
>> +++ b/hw/block/virtio-blk.c
>> @@ -381,7 +381,7 @@ void virtio_blk_submit_multireq(BlockBackend *blk, MultiReqBuffer *mrb)
>>       }
>>         max_xfer_len = blk_get_max_transfer_length(mrb->reqs[0]->dev->blk);
>> -    max_xfer_len = MIN_NON_ZERO(max_xfer_len, INT_MAX);
>> +    max_xfer_len = MIN_NON_ZERO(max_xfer_len, BDRV_REQUEST_MAX_SECTORS);
>>         qsort(mrb->reqs, mrb->num_reqs, sizeof(*mrb->reqs),
>>             &multireq_compare);
>> @@ -447,7 +447,7 @@ static bool virtio_blk_sect_range_ok(VirtIOBlock *dev,
>>       uint64_t nb_sectors = size >> BDRV_SECTOR_BITS;
>>       uint64_t total_sectors;
>>   -    if (nb_sectors > INT_MAX) {
>> +    if (nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
>>           return false;
>>       }
>>       if (sector & dev->sector_mask) {
>> diff --git a/include/block/block.h b/include/block/block.h
>> index 3082d2b..25a6d62 100644
>> --- a/include/block/block.h
>> +++ b/include/block/block.h
>> @@ -83,6 +83,9 @@ typedef enum {
>>   #define BDRV_SECTOR_SIZE   (1ULL << BDRV_SECTOR_BITS)
>>   #define BDRV_SECTOR_MASK   ~(BDRV_SECTOR_SIZE - 1)
>>   +#define BDRV_REQUEST_MAX_SECTORS MIN(SIZE_MAX >> BDRV_SECTOR_BITS, \
>> +                                     INT_MAX >> BDRV_SECTOR_BITS)
>> +
>>   /*
>>    * Allocation status flags
>>    * BDRV_BLOCK_DATA: data is read from bs->file or another file
> Reviewed-by: Denis V. Lunev <den@openvz.org>
>
> On the other hand the limitation to INT_MAX for a request size
> (in bytes) is here.
>
> bdrv_check_byte_request
>     if (size > INT_MAX) {
>         return -EIO;
>     }
>
> which means that all my patches from series
>   [PATCH v3 0/2] fix max_discard for NBD/gluster block drivers
> becomes unnecessary but this was not that obvious before this
> clarification :)

No, not completely. If we run into the check above the request fails.
If you set max_write_zeroes the request is appropiately trimmed.
So if the driver allows less than BDRV_REQUEST_MAX_SECTORS sectors
you still have to set it in the BlockLimits.

Peter