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Re: [Qemu-block] [Qemu-devel] [PATCH v3 04/13] netmap: Drop netmap_can_s


From: Stefan Hajnoczi
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v3 04/13] netmap: Drop netmap_can_send
Date: Tue, 19 May 2015 15:54:33 +0100
User-agent: Mutt/1.5.23 (2014-03-12)

On Tue, May 19, 2015 at 10:51:01AM +0000, Fam Zheng wrote:
> This callback is called by main loop before polling s->fd, if it returns
> false, the fd will not be polled in this iteration.
> 
> This is redundant with checks inside read callback. After this patch,
> the data will be copied from s->fd to s->iov when it arrives. If the
> device can't receive, it will be queued to incoming_queue, and when the
> device status changes, this queue will be flushed.
> 
> Also remove the qemu_can_send_packet() check in netmap_send. If it's
> true, we are good; if it's false, the qemu_sendv_packet_async would
> return 0 and read poll will be disabled until netmap_send_completed is
> called.

This causes unbounded memory usage in QEMU because
qemu_net_queue_append_iov() does not drop packets when sent_cb != NULL.

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