linux-kernel - Re: [PATCH] Modify the return value ret to EOPNOTSUPP when initialized to reduce repeated assignment of errno

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Date:   Thu, 11 Aug 2022 20:42:22 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Zhang chunchao <chunchao@...china.com>
Cc:     Zhang chunchao <chunchao@...china.com>, asml.silence@...il.com,
        io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...china.com
Subject: Re: [PATCH] Modify the return value ret to EOPNOTSUPP when
 initialized to reduce repeated assignment of errno

On Thu, Aug 11, 2022 at 09:41:38AM -0600, Jens Axboe wrote:
>On 8/11/22 9:02 AM, Stefano Garzarella wrote:
>> On Thu, Aug 11, 2022 at 03:56:38PM +0800, Zhang chunchao wrote:
>>> Remove unnecessary initialization assignments.
>>>
>>> Signed-off-by: Zhang chunchao <chunchao@...china.com>
>>> ---
>>> io_uring/io_uring.c | 3 +--
>>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
>>> index b54218da075c..8c267af06401 100644
>>> --- a/io_uring/io_uring.c
>>> +++ b/io_uring/io_uring.c
>>> @@ -3859,14 +3859,13 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
>>>         void __user *, arg, unsigned int, nr_args)
>>> {
>>>     struct io_ring_ctx *ctx;
>>> -    long ret = -EBADF;
>>> +    long ret = -EOPNOTSUPP;
>>>     struct fd f;
>>>
>>>     f = fdget(fd);
>>>     if (!f.file)
>>>         return -EBADF;
>>>
>>> -    ret = -EOPNOTSUPP;
>>>     if (!io_is_uring_fops(f.file))
>>>         goto out_fput;
>>>
>>
>> What about remove the initialization and assign it in the if branch?
>> I find it a bit easier to read.
>>
>> I mean something like this:
>>
>> --- a/io_uring/io_uring.c
>> +++ b/io_uring/io_uring.c
>> @@ -3859,16 +3859,17 @@ SYSCALL_DEFINE4(io_uring_register, unsigned int, fd, unsigned int, opcode,
>>                 void __user *, arg, unsigned int, nr_args)
>>  {
>>         struct io_ring_ctx *ctx;
>> -       long ret = -EBADF;
>> +       long ret;
>>         struct fd f;
>>
>>         f = fdget(fd);
>>         if (!f.file)
>>                 return -EBADF;
>>
>> -       ret = -EOPNOTSUPP;
>> -       if (!io_is_uring_fops(f.file))
>> +       if (!io_is_uring_fops(f.file)) {
>> +               ret = -EOPNOTSUPP;
>>                 goto out_fput;
>> +       }
>>
>>         ctx = f.file->private_data;
>>
>>
>> Otherwise remove the initialization, but leave the assignment as it is now.
>
>Generally the kernel likes to do:
>
>err = -EFOO;
>if (something)
>	goto err_out;
>
>rather than put it inside the if clause. I guess the rationale is it
>makes it harder to forget to init the error value. I don't feel too

ah, thanks for pointing this out! Make sense to me, but I hope recent 
compilers can spot that kind of issue :-)

>strongly, I'm fine with your patch too. Can you send it as a real patch?

@Zhang: if you want, feel free to change your patch following the 
suggestions and send a new version, otherwise I can send mine of course.

Thanks,
Stefano