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Subject: Re: [PATCH v7 06/15] iomap: Return error code from iomap_write_iter()
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To: Matthew Wilcox <willy@infradead.org>
Cc: io-uring@vger.kernel.org, kernel-team@fb.com, linux-mm@kvack.org,
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<20220601210141.3773402-7-shr@fb.com> <YpivQhqhZxwvdDUm@casper.infradead.org>
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On 6/2/22 5:38 AM, Matthew Wilcox wrote:
> On Wed, Jun 01, 2022 at 02:01:32PM -0700, Stefan Roesch wrote:
>> Change the signature of iomap_write_iter() to return an error code. In
>> case we cannot allocate a page in iomap_write_begin(), we will not retry
>> the memory alloction in iomap_write_begin().
>
> loff_t can already represent an error code. And it's already used like
> that.
>
>> @@ -829,7 +830,8 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
>> length -= status;
>> } while (iov_iter_count(i) && length);
>>
>> - return written ? written : status;
>> + *processed = written ? written : error;
>> + return error;
>
> I think the change you really want is:
>
> if (status == -EAGAIN)
> return -EAGAIN;
> if (written)
> return written;
> return status;
>
I think the change needs to be:
- return written ? written : status;
+ if (status == -EAGAIN) {
+ iov_iter_revert(i, written);
+ return -EAGAIN;
+ }
+ if (written)
+ return written;
+ return status;
>> @@ -843,12 +845,15 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *i,
>> .flags = IOMAP_WRITE,
>> };
>> int ret;
>> + int error = 0;
>>
>> if (iocb->ki_flags & IOCB_NOWAIT)
>> iter.flags |= IOMAP_NOWAIT;
>>
>> - while ((ret = iomap_iter(&iter, ops)) > 0)
>> - iter.processed = iomap_write_iter(&iter, i);
>> + while ((ret = iomap_iter(&iter, ops)) > 0) {
>> + if (error != -EAGAIN)
>> + error = iomap_write_iter(&iter, i, &iter.processed);
>> + }
>
> You don't need to change any of this. Look at how iomap_iter_advance()
> works.
>