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From: Wei Liu <wei.liu2@citrix.com>
To: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Anthony PERARD <anthony.perard@citrix.com>,
	Xen-devel <xen-devel@lists.xenproject.org>,
	Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH v3 4/5] libxl: update vcpus bitmap in retrieved guest config
Date: Mon, 11 Jul 2016 12:31:43 +0100	[thread overview]
Message-ID: <20160711113143.GG7019@citrix.com> (raw)
In-Reply-To: <22399.59004.935094.420724@mariner.uk.xensource.com>

On Fri, Jul 08, 2016 at 06:44:28PM +0100, Ian Jackson wrote:
> Wei Liu writes ("[PATCH v3 4/5] libxl: update vcpus bitmap in retrieved guest config"):
> > ... because the available vcpu bitmap can change during domain life time
> > due to cpu hotplug and unplug.
> > 
> > For QEMU upstream, we interrogate QEMU for the number of vcpus. For
> > others, we look directly into xenstore for information.
> ...
> > +static int libxl__update_avail_vcpus_qmp(libxl__gc *gc, uint32_t domid,
> > +                                         unsigned int max_vcpus,
> > +                                         libxl_bitmap *map)
> > +{
> > +    int rc;
> > +
> > +    /* For QEMU upstream we always need to return the number
> > +     * of cpus present to QEMU whether they are online or not;
> > +     * otherwise QEMU won't accept the saved state.
> 
> This comment is confusing to me.  Perhaps `return' should read
> `provide' ?  But the connection between the body of this function and
> the comment is still obscure.
> 

"provide" is ok.

To avoid confusion the comment can be moved a few line above to describe
the function, not the code snippet. Does that work better?

> > +static int libxl__update_avail_vcpus_xenstore(libxl__gc *gc, uint32_t domid,
> > +                                              unsigned int max_vcpus,
> > +                                              libxl_bitmap *map)
> > +{
> > +    int rc;
> > +    unsigned int i;
> > +    const char *dompath;
> ...
> > +    for (i = 0; i < max_vcpus; i++) {
> > +        const char *path = GCSPRINTF("%s/cpu/%u/availability", dompath, i);
> > +        const char *content = libxl__xs_read(gc, XBT_NULL, path);
> > +        if (!strcmp(content, "online"))
> > +            libxl_bitmap_set(map, i);
> 
> Firstly, this should be libxl__xs_read_checked.  Secondly if "content"
> is NULL, this will crash.
> 

Will fix.

> > @@ -7294,6 +7341,55 @@ int libxl_retrieve_domain_configuration(libxl_ctx *ctx, uint32_t domid,
> >          libxl_dominfo_dispose(&info);
> >      }
> >  
> > +    /* VCPUs */
> > +    {
> > +        libxl_bitmap *map = &d_config->b_info.avail_vcpus;
> > +        unsigned int max_vcpus = d_config->b_info.max_vcpus;
> > +        libxl_device_model_version version;
> > +
> > +        libxl_bitmap_dispose(map);
> > +        libxl_bitmap_init(map);
> > +        libxl_bitmap_alloc(CTX, map, max_vcpus);
> > +        libxl_bitmap_set_none(map);
> 
> I see that this function already trashes the domain config when it
> fails (leaving it up to the caller to free the partial config) but
> that this is not documented :-/.

d_config is an out parameter. User can't expect the returned d_config to
be valid if this API returns error state. And user is still responsible
for calling _init before calling this API and _dispose afterwards. So
this still fits into how we expect libxl types to be used. Nothing new
needs to be documented.

All other fields are already handled in this way.

> 
> > +        /* If the user did not explicitly specify a device model
> > +         * version, we need to use the same logic used during domain
> > +         * creation to derive the device model version.
> > +         */
> > +        version = d_config->b_info.device_model_version;
> > +        if (version == LIBXL_DEVICE_MODEL_VERSION_UNKNOWN)
> > +            version = libxl__get_device_model_version(gc, &d_config->b_info);
> 
> I think this is rather unfortunate.  Won't changing the default device
> model while the domain is running will cause this function to give
> wrong answers ?

I think saving the device model into the template should work. No need
to derive it during runtime.

Wei.

> 
> Thanks,
> Ian.

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  reply	other threads:[~2016-07-11 11:31 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-15  9:31 [PATCH v3 0/5] libxl: libxl: update available vcpus map in retrieve configuration function Wei Liu
2016-06-15  9:31 ` [PATCH v3 1/5] libxl: libxl_domain_need_memory shouldn't modify b_info Wei Liu
2016-06-15 13:31   ` Dario Faggioli
2016-06-15 13:38     ` Wei Liu
2016-07-08 17:35   ` Ian Jackson
2016-07-11 11:03     ` Wei Liu
2016-06-15  9:31 ` [PATCH v3 2/5] libxl: factor out libxl__get_device_modlel_version Wei Liu
2016-06-15 13:27   ` Dario Faggioli
2016-06-15 17:04   ` Anthony PERARD
2016-07-08 17:37   ` Ian Jackson
2016-06-15  9:31 ` [PATCH v3 3/5] libxl: introduce libxl__qmp_query_cpus Wei Liu
2016-06-15 13:26   ` Dario Faggioli
2016-06-15 16:48   ` Anthony PERARD
2016-07-08 17:45   ` Ian Jackson
2016-06-15  9:31 ` [PATCH v3 4/5] libxl: update vcpus bitmap in retrieved guest config Wei Liu
2016-06-15 17:20   ` Anthony PERARD
2016-07-08 17:44   ` Ian Jackson
2016-07-11 11:31     ` Wei Liu [this message]
2016-07-11 14:59       ` Wei Liu
2016-06-15  9:31 ` [PATCH v3 5/5] libxl: only issue cpu-add call to QEMU for not present CPU Wei Liu
2016-07-08 17:48   ` Ian Jackson
2016-07-11 11:32     ` Wei Liu
2016-07-02 10:22 ` [PATCH v3 0/5] libxl: libxl: update available vcpus map in retrieve configuration function Wei Liu

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