On Mon, 7 Jun 2010 07:54:41 am Herbert Xu wrote:

On Sun, Jun 06, 2010 at 11:13:00PM +0300, Michael S. Tsirkin wrote:

quoted

Actually this code looks strange:
Note that add_buf inicates out of memory
condition with a positive return value, and ring full
(which is not an error!) with -ENOSPC.

Indeed, this ultimately came from

commit 9ab86bbcf8be755256f0a5e994e0b38af6b4d399
Author: Shirley Ma [off-list ref]
Date:   Fri Jan 29 03:20:04 2010 +0000

    virtio_net: Defer skb allocation in receive path Date: Wed, 13 Jan 2010 12:53:38 -0800

(Greg, please don't apply this even though I've just given you
the upstream commit ID that you were asking for :)

where it confuses a memory allocation error with an add_buf failure.

quoted

Possibly the right thing to do is to
1. handle ENOMEM specially
2. fix add_buf to return ENOMEM on error

I think we should make it so that only a memory allocation error
is returned as before.  There is no need for returning the add_buf
error unless add_buf is now doing an allocation itself that needs
to be retried.

With indirect bufs, this is indeed the case.  The code works except
for the bigpackets !mergable case, but should be clarified anyway.

See my other mail...

Thanks,
Rusty.