Re: [Xen-devel] [PATCH 06/18] lib{xc, xl}: Seed grant tables with xenstore and console grants

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 01/12/2012 04:59 AM, Ian Campbell wrote:
> On Wed, 2012-01-11 at 17:21 +0000, Daniel De Graaf wrote:
>> From: Alex Zeffertt <alex.zeffertt@xxxxxxxxxxxxx>
>>
>> This patch claims one reserved grant entry for the console and another
>> for the xenstore. It modifies the builder to fill in the grant table
>> entries for the console and the xenstore.
>>
>> This has not been tested with any kind of migration.
>>
> [...]
>> diff --git a/tools/libxc/xc_domain_restore.c 
>> b/tools/libxc/xc_domain_restore.c
>> index 3fda6f8..23619da 100644
>> --- a/tools/libxc/xc_domain_restore.c
>> +++ b/tools/libxc/xc_domain_restore.c
>> @@ -2018,6 +2018,15 @@ int xc_domain_restore(xc_interface *xch, int io_fd, 
>> uint32_t dom,
>>          memcpy(ctx->live_p2m, ctx->p2m, dinfo->p2m_size * 
>> sizeof(xen_pfn_t));
>>      munmap(ctx->live_p2m, P2M_FL_ENTRIES * PAGE_SIZE);
>>
>> +/* TODO don't hardcode zero here */
>> +    rc = xc_dom_gnttab_seed(xch, dom,
>> +                            *console_mfn, *store_mfn, 0, 0);
> 
> Presumably this TODO is the source of the comment in the changelog WRT
> migration.
> 
> Does it Just Work or is there a legitimate TODO item here?
> 
> Ian.
> 
> 

This causes migration to only work if xenstored/xenconsoled are both in
dom0, as the domain ID for both of them are hardcoded to zero. Determining
the correct values for these domain IDs is more difficult than the domain
build case, because they may not be the same as when the domain was built
(especially if we are migrating).

The previous patch series used a domid file named similarly to a pid file
to identify the location of xenstored and xenconsoled; this method would
allow the TODO to be resolved. I think a better solution is to refer to the
xenstore/xenconsole domains by name instead of domid, and set the names in
a configuration file (/etc/xen/xl.conf?). This would also replace the
xenstore_dom/console_dom parameters in patch #5.

-- 
Daniel De Graaf
National Security Agency

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