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

["Denis V. Lunev" <den@parallels.com>]

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;
      }

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