Re: [RFC 0/3] 64bit block-layer part I

[Eric Blake <eblake@redhat.com>]

On 4/22/20 9:29 AM, Vladimir Sementsov-Ogievskiy wrote:
> Any thoughts here? I need to resend to update some more functions as 
> patchew said.
> 
> Is it OK in general? Or should we instead convert everything to uint64_t ?

I definitely prefer int64_t as our base (off_t is signed as well, making 
63 bits an effective limit everywhere).

> 
> 30.03.2020 17:18, Vladimir Sementsov-Ogievskiy wrote:
>> Hi all!
>>
>> There is an idea to make NBD protocol extension to support 64bit
>> write-zero/discard/block-status commands (commands, which doesn't
>> transfer user data). It's needed to increase performance of zeroing
>> large ranges (up to the whole image). Zeroing of the whole image is used
>> as first step of mirror job, qemu-img convert, it should be also used at
>> start of backup actually..
>>
>> We need to support it in block-layer, so we want 64bit write_zeros.
>> Currently driver handler now have int bytes parameter.
>>
>> write_zeros path goes through normal pwritev, so we need 64bit write,
>> and then we need 64bit read for symmetry, and better, let's make all io
>> path work with 64bit bytes parameter.
>>
>> Actually most of block-layer already have 64bit parameters: offset is
>> sometimes int64_t and sometimes uint64_t. bytes parameter is one of
>> int64_t, uint64_t, int, unsigned int...
>>
>> I think we need one type for all of this, and this one type is int64_t.
>> Signed int64_t is a bit better than uint64_t: you can use same variable
>> to get some result (including error < 0) and than reuse it as an
>> argument without any type conversion.
>>
>> So, I propose, as a first step, convert all uint64_t parameters to
>> int64_t.

Makes sense.  I haven't looked at the series closely in part because it 
was 5.1 material while we were still focused on getting 5.0 out the 
door, but it is now raising in my review queue again.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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