Re: [Xen-devel] [PATCH v3 7/7] libxl/vcpu-set - allow to decrease vcpu count on overcommitted guests (v3)

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-03-23 at 14:21 -0400, Konrad Rzeszutek Wilk wrote:
> We have a check to warn the user if they are overcommitting.
> But the check only checks the hosts CPU amount and does
> not take into account the case when the user is trying to fix
> the overcommit. That is - they want to limit the amount of
> online VCPUs.
> 
> This fix allows the user to offline vCPUs without any
> warnings when they are running an overcommitted guest.
> 
> Also fix the extra space in the message.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 
> ---
> [v2: Remove crud code as spotted by Boris]
> [v3: Moved crud code removal to another patch]
> ---
>  tools/libxl/xl_cmdimpl.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
> index b121d75..d7bd5d5 100644
> --- a/tools/libxl/xl_cmdimpl.c
> +++ b/tools/libxl/xl_cmdimpl.c
> @@ -5238,9 +5238,18 @@ static int vcpuset(uint32_t domid, const char* 
> nr_vcpus, int check_host)
>       */
>      if (check_host) {
>          unsigned int host_cpu = libxl_get_max_cpus(ctx);
> -        if (max_vcpus > host_cpu) {
> -            fprintf(stderr, "You are overcommmitting! You have %d physical " 
> \
> -                    " CPUs and want %d vCPUs! Aborting, use --ignore-host to 
> " \
> +        libxl_dominfo dominfo;
> +
> +        rc = libxl_domain_info(ctx, &dominfo, domid);
> +        if (rc)
> +        {
> +             if (rc == ERROR_DOMAIN_NOTFOUND)
> +                fprintf(stderr, "Domain %u does not exist.\n", domid);
> +            return 1;

Indentation is wrong on the if.

More generally all of these rc == ERROR_DOMAIN_NOTFOUND check and prints
are going to get rather tiresome, especially if/when there are other
interesting error codes. Perhaps we could arrange for something further
down the stack on libxl to log this sort of thing, such that xl can rely
on it already having been mentioned?

e.g. libxl_domain_info could do it perhaps?

Or perhaps a helper (in xl?) which produces some common logging for
common errors which could be called?


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