Re: [PATCH 1/4] fs: make do_loop_readv_writev() deal with ITER_UBUF

[Jens Axboe <axboe@kernel.dk>]

On 3/27/23 1:03?PM, Linus Torvalds wrote:
> On Mon, Mar 27, 2023 at 11:04?AM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> --- a/fs/read_write.c
>> +++ b/fs/read_write.c
>> @@ -748,10 +748,21 @@ static ssize_t do_loop_readv_writev(struct file *filp, struct iov_iter *iter,
>>         if (flags & ~RWF_HIPRI)
>>                 return -EOPNOTSUPP;
>>
>> +       if (WARN_ON_ONCE(iter->iter_type != ITER_IOVEC &&
>> +                        iter->iter_type != ITER_UBUF))
>> +               return -EINVAL;
> 
> Hmm. I think it might actually be nicer for the "iter_is_ubuf(iter)"
> case to be outside the loop entirely, and be done before this
> WARN_ON_ONCE().
> 
> If it's a single ITER_UBUF, that code really shouldn't loop at all -
> it's literally just the old case of "call ->read/write with a single
> buffer".
> 
> So i think I'd prefer this patch to be something along the lines of
> this instead:

See Al's suggestion in the other thread, I like that a lot better as it
avoids any potential wack-a-mole with potentially similar cases. There
are not a lot of hits for iov_iter_iovec() in the three and I spotted
two, which lead to these two prep patches. But if we do:

https://git.kernel.dk/cgit/linux-block/commit/?h=iter-ubuf&id=8a825a6f52e8fab74e936f15eea6c34ac67272f6

then we don't really have to worry about those.

-- 
Jens Axboe