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[Qemu-devel] Re: Extending virtio_console to support multiple ports

From: Amit Shah
Subject: [Qemu-devel] Re: Extending virtio_console to support multiple ports
Date: Wed, 26 Aug 2009 16:57:18 +0530
User-agent: Mutt/1.5.19 (2009-01-05)

On (Tue) Aug 25 2009 [11:47:20], Amit Shah wrote:
> Hello all,
> Here is a new iteration of the patch series that implements a
> transport for guest and host communications.
> The code has been updated to reuse the virtio-console device instead
> of creating a new virtio-serial device.

And the problem now is that hvc calls the put_chars function with
spinlocks held and we now allocate pages in send_buf(), called from

A few solutions:
- Keep things as they are, virtio_console.c remains as it is and
  virtio_serial.c gets added

- Have separate write paths for console devices in virtio_console.c,
  which would beat the purpose of merging the two drivers and then
  they'd be better off standalone

- Convert hvc's usage of spinlocks to mutexes. I've no idea how this
  will play out; I'm no expert here. But I did try doing this and so far
  it all looks OK. No lockups, lockdep warnings, nothing. I have full
  debugging enabled. But this doesn't mean it's right.



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