Re: [PATCH 0/5] io_uring: add opcodes for current working directory

From: Usama Arif <usama.arif@bytedance.com>
To: Jens Axboe <axboe@kernel.dk>,
	io-uring@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: fam.zheng@bytedance.com
Subject: Re: [PATCH 0/5] io_uring: add opcodes for current working directory
Date: Tue, 31 May 2022 22:35:46 +0100	[thread overview]
Message-ID: <f7a4cdf2-78f2-fead-5a10-713e3dc9ea34@bytedance.com> (raw)
In-Reply-To: <d466213e-81e0-4b0e-c1a4-824bcbe42f74@kernel.dk>

On 31/05/2022 20:22, Jens Axboe wrote:
> On 5/31/22 1:18 PM, Usama Arif wrote:
>>
>>
>> On 31/05/2022 19:58, Jens Axboe wrote:
>>> On 5/31/22 12:41 PM, Usama Arif wrote:
>>>> This provides consistency between io_uring and the respective I/O syscall
>>>> and avoids having the user of liburing specify the cwd in sqe when working
>>>> with current working directory, for e.g. the user can directly call with
>>>> IORING_OP_RENAME instead of IORING_OP_RENAMEAT and providing AT_FDCWD in
>>>> sqe->fd and sqe->len, similar to syscall interface.
>>>>
>>>> This is done for rename, unlink, mkdir, symlink and link in this
>>>> patch-series.
>>>>
>>>> The tests for these opcodes in liburing are present at
>>>> https://github.com/uarif1/liburing/tree/cwd_opcodes. If the patches are
>>>> acceptable, I am happy to create a PR in above for the tests.
>>>
>>> Can't we just provide prep helpers for them in liburing?
>>>
>>
>> We could add a io_uring_prep_unlink with IORING_OP_UNLINKAT and
>> AT_FDCWD in liburing. But i guess adding in kernel adds a more
>> consistent interface? and allows to make calls bypassing liburing
>> (although i guess people probably don't bypass liburing that much :))
> 
> I'm not really aware of much that doesn't use the library, and even
> those would most likely use the liburing man pages as that's all we
> have. The kernel API is raw. If you use that, I would expect you to know
> that you can just use AT_FDCWD!
> 
>> Making the changes in both kernel and liburing provides more of a
>> standard interface in my opinion so maybe it looks better. But happy
>> to just create a PR in liburing only with prep helpers as you
>> suggested if you think that is better?
> 
> I don't disagree with that, but it seems silly to waste 5 opcodes on
> something that is a strict subset of something that is already there.
> Hence my suggestion would be to just add io_uring_prep_link() etc
> helpers to make it simpler to use, without having to add 5 extra
> opcodes.
> 

Thanks, I have created a PR for it on 
https://github.com/axboe/liburing/pull/588. We can review it there if it 
makes sense!