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

[Peter Lieven <pl@kamp.de>]

Am 03.02.2015 um 16:33 schrieb Denis V. Lunev:
> On 03/02/15 17:30, Peter Lieven wrote:
>> 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
>>
> your point will be correct after the following patch applied
>
> diff --git a/block.c b/block.c
> index 4e58b35..49e0073 100644
> --- a/block.c
> +++ b/block.c
> @@ -2647,7 +2647,7 @@ static int bdrv_check_byte_request(BlockDriverState *bs, i
>  {
>      int64_t len;
>
> -    if (size > INT_MAX) {
> +    if (size > BDRV_REQUEST_MAX_SECTORS << BDRV_SECTOR_BITS) {
>          return -EIO;
>      }

You are right, this will still fail if SIZE_MAX < INT_MAX. I would send a v2 of my
patch and add the above. Then Kevin can remove your 2 patches, right?

Peter

>
> without we will fail at entry point inside bdrv_check_byte_request().
> My patch applies the limit of UINT32_MAX over the value which
> is not greater than INT_MAX in the current codebase.
> bdrv_check_byte_request() is performed at the very-very beginning
> of the processing, f.e
>
> bdrv_co_discard
>   bdrv_check_request
>       bdrv_check_byte_request <-- (INT_MAX limit applied)
>   max_discard = MIN_NON_ZERO(bs->bl.max_discard, BDRV_REQUEST_MAX_SECTORS);
>
> Den