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Date: Tue, 06 Apr 2010 13:16:16 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/5] char: Let the caller know how many	bytes
	were written in case of incomplete writes
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To: Amit Shah <amit.shah@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>, Paul Brook <paul@codesourcery.com>, qemu-devel@nongnu.org

On 04/06/10 13:05, Amit Shah wrote:
> On (Tue) Apr 06 2010 [12:21:52], Gerd Hoffmann wrote:
>> On 04/06/10 11:58, Amit Shah wrote:
>>>>> It would certainly be beneficial for consumers of virtio-serial to be
>>>>> notified of -EAGAIN so that the guest can be throttled till the chardev
>>>>> catches up with the data being sent.
>>>>
>>>> EAGAIN should only ever occur if no bytes are written.
>>>
>>> Right. That, or just return 0 and let the caller handle the situation?
>>
>> Go with the usual unix semantics instead of creating something new.
>>
>> When something was written -- return the number of bytes.  Caller has to
>> compare with the length passed in to figure whenever it was a partial
>> write or not.
>>
>> When nothing was written -- return the error.
>
> Unless Paul wants to never return recoverable error messages as he
> mentioned in his first mail.

Return value "0" usually means end-of-file, I would not use that for 
something else too.  We have to agree on something though ...

cheers,
   Gerd