Re: [PATCH v7 06/15] iomap: Return error code from iomap_write_iter()

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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.
> 



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