[Devel] [PATCH RH9 v4 01/10] drivers/vhost: vhost-blk accelerator for virtio-blk guests

[Pavel Tikhomirov]

On 04.11.2022 15:28, Andrey Zhadchenko wrote:
> 
> 
> On 11/4/22 14:31, Pavel Tikhomirov wrote:
>>
>>
>> On 01.11.2022 10:25, Andrey Zhadchenko wrote:
>>> +/* It is forbidden to call more than one vhost_blk_flush() 
>>> simultaneously */
>>> +static void vhost_blk_flush(struct vhost_blk *blk)
>>> +{
>>> +    int flush_bin;
>>> +
>>> +    spin_lock(&blk->flush_lock);
>>> +    blk->during_flush = 1;
>>> +    flush_bin = blk->new_req_bin;
>>> +    blk->new_req_bin = (blk->new_req_bin) ? 0 : 1;
>>
>> We can use shorter and simpler expression for this:
>>
>> blk->new_req_bin = !blk->new_req_bin;
> 
> Are you sure C standard actually defines it this way and we are not 
> relying on unspecified behavior?
> I thought ! operator only defined for logical expressions

C99 6.5.3.3.5 says:
"The result of the logical negation operator ! is 0 if the value of its 
operand compares
unequal to 0, 1 if the value of its operand compares equal to 0. The 
result has type int.
The expression !E is equivalent to (0==E)"
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf

So I don't see any problem comparing new_req_bin of type int to 0.

> 
>>
>>> +    spin_unlock(&blk->flush_lock);
>>

-- 
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.