Re: [Xen-devel] [PATCH] libxl: default to xenconsoled for pv guests, even if qemu is running

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 25 Apr 2012, Ian Campbell wrote:
> # HG changeset patch
> # User Ian Campbell <ian.campbell@xxxxxxxxxx>
> # Date 1335348624 -3600
> # Node ID c8486295429011e9a220db1b6ed9f34ba690e729
> # Parent  6f740f2f6e3e080e4bba9df59c826947885f6bd7
> libxl: default to xenconsoled for pv guests, even if qemu is running.
> 
> Currently we prefer to use qemu for the disk backend if we are starting qemu
> anyway (e.g. to service a disk).
> 
> Unfortunately qemu doesn't log the console, which xenconsoled can do via
> XENCONSOLED_TRACE=guest. Since xenconsoled is also running anyway it seems 
> like
> there is no particular reason to prefer qemu just because it happens to be
> running.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

QEMU's console backend supports multiple PV consoles while xenconsoled
does not.
I think you should just change the default only in case a single PV
console is configured.


> I'm not sure if this is 4.2 material, perhaps too late to be making this sort
> of change?
> 
> diff -r 6f740f2f6e3e -r c84862954290 tools/libxl/libxl_create.c
> --- a/tools/libxl/libxl_create.c      Wed Apr 25 11:05:05 2012 +0100
> +++ b/tools/libxl/libxl_create.c      Wed Apr 25 11:10:24 2012 +0100
> @@ -682,8 +682,7 @@ static int do_domain_create(libxl__gc *g
>                  d_config->num_vfbs, d_config->vfbs,
>                  d_config->num_disks, &d_config->disks[0]);
>  
> -        if (need_qemu)
> -             console.consback = LIBXL__CONSOLE_BACKEND_IOEMU;
> +        console.consback = LIBXL__CONSOLE_BACKEND_XENCONSOLED;
>  
>          libxl__device_console_add(gc, domid, &console, &state);
>          libxl__device_console_dispose(&console);

I would change the if into:

if (need_qemu and nr_console > 1)

even though I am aware that at the moment nr_console is always 1.


> diff -r 6f740f2f6e3e -r c84862954290 tools/libxl/libxl_dm.c
> --- a/tools/libxl/libxl_dm.c  Wed Apr 25 11:05:05 2012 +0100
> +++ b/tools/libxl/libxl_dm.c  Wed Apr 25 11:10:24 2012 +0100
> @@ -1093,11 +1093,6 @@ int libxl__need_xenpv_qemu(libxl__gc *gc
>  {
>      int i, ret = 0;
>  
> -    if (nr_consoles > 1) {
> -        ret = 1;
> -        goto out;
> -    }
> -

I would get rid of this change

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