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

[Stefano Garzarella]

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@xxxxxxxxxxxx>
> > > ---
> > > 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