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Re: [Qemu-devel] [PATCH 1/5] char: Let the caller know how many bytes we

From: Amit Shah
Subject: Re: [Qemu-devel] [PATCH 1/5] char: Let the caller know how many bytes were written in case of incomplete writes
Date: Tue, 6 Apr 2010 08:54:29 +0530
User-agent: Mutt/1.5.19 (2009-01-05)

On (Mon) Apr 05 2010 [17:33:38], Paul Brook wrote:
> > There might be cases where a few bytes would have been sent out to char
> > devices and some not. Currently the return values from qemu_chr_write()
> > to char devs are only -1, indicating an error, or the complete length
> > of the string passed.
> > 
> > Make 'len' a pointer instead, and indicate how much of the string was
> > written. The return value will either be the same as 'len' or a negative
> > number indicating an error condition.
> This seems wrong. We should not be getting recoverable errors.

I was thinking of adding a bool to CharDriverState to indicate if EAGAIN
should be reported to the writer. This can be conveyed at the time of
doing qemu_chr_add_handlers().

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.


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