Re: [RFC PATCH 2/2] tools/cpupools: Give a name to unnamed cpupools

[Juergen Gross <jgross@xxxxxxxx>]

On 17.11.21 12:52, Luca Fancellu wrote:
> > On 17 Nov 2021, at 11:10, Juergen Gross <jgross@xxxxxxxx> wrote:
> >
> > On 17.11.21 10:57, Luca Fancellu wrote:
> > > With the introduction of boot time cpupools, Xen can
> > > create at boot time many cpupools different from the
> > > cpupool with id 0.
> > > Since these newly created cpupools can't have an
> > > entry in Xenstore, name them with the same convention
> > > used for the cpupool 0: Pool-<cpupool id>.
> > > Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> > > ---
> > >   tools/libs/light/libxl_utils.c | 13 ++++++++-----
> > >   1 file changed, 8 insertions(+), 5 deletions(-)
> > > diff --git a/tools/libs/light/libxl_utils.c b/tools/libs/light/libxl_utils.c
> > > index 4699c4a0a3..d97d91ca98 100644
> > > --- a/tools/libs/light/libxl_utils.c
> > > +++ b/tools/libs/light/libxl_utils.c
> > > @@ -147,13 +147,16 @@ int libxl_cpupool_qualifier_to_cpupoolid(libxl_ctx *ctx, 
> > > const char *p,
> > >   char *libxl_cpupoolid_to_name(libxl_ctx *ctx, uint32_t poolid)
> > >   {
> > >       unsigned int len;
> > > -    char path[strlen("/local/pool") + 12];
> > > +    char buffer[strlen("/local/pool") + 12];
> > >       char *s;
> > >   -    snprintf(path, sizeof(path), "/local/pool/%d/name", poolid);
> > > -    s = xs_read(ctx->xsh, XBT_NULL, path, &len);
> > > -    if (!s && (poolid == 0))
> > > -        return strdup("Pool-0");
> > > +    snprintf(buffer, sizeof(buffer), "/local/pool/%d/name", poolid);
> > > +    s = xs_read(ctx->xsh, XBT_NULL, buffer, &len);
> > > +    if (!s)
> > > +    {
> > > +        snprintf(buffer, sizeof(buffer), "Pool-%d", poolid);
> > > +        return strdup(buffer);
> > > +    }
> > >       return s;
> > >   }
> > >   
> > This breaks libxl_cpupoolid_is_valid(), as it will now return always
> > true, regardless whether the poolid is existing or not.
> Hi Juergen,
>
> Yes right, do you think I can use safely xc_cpupool_getinfo(…) when there is no 
> entry
> in xenstore?
> I would check that the returned cpupool id is the same and if it isn’t or if I 
> get a null
> result, then I will return NULL to ensure libxl_cpupoolid_is_valid(…) works 
> again.
An alternative might be to let tools/helpers/xen-init-dom0.c let write
the missing cpupool entries (including for Pool-0) and drop the
poolid == 0 special casing from libxl_cpupoolid_to_name().

This should be rather easy by using xc_cpupool_getinfo() until it finds
no further cpupool.


Juergen

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