Re: [Xen-devel] [PATCH 2/2] dom_cow is needed for mem-sharing only

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.05.19 at 19:13, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 31/05/2019 02:35, Jan Beulich wrote:
>> A couple of adjustments are needed to code checking for dom_cow, but
>> since there are pretty few it is probably better to adjust those than
>> to set up and keep around a never used domain.
>>
>> Take the opportunity and tighten a BUG_ON() in emul-priv-op.c:read_cr().
>> (Arguably this perhaps shouldn't be a BUG_ON() in the first place.)
> 
> Yes - it should be ASSERT_UNREACHABLE()/domain_crash()
> 
> I'm not fussed if this done as part of this patch, or split out
> separately.  It almost doesn't seem worth splitting out.

Well, to do both changes at the same time, I'll really split this out
into a prereq patch.

>> --- a/xen/include/xen/mm.h
>> +++ b/xen/include/xen/mm.h
>> @@ -644,6 +644,9 @@ static inline void filtered_flush_tlb_ma
>>  
>>  /* Private domain structs for DOMID_XEN, DOMID_IO, etc. */
>>  extern struct domain *dom_xen, *dom_io, *dom_cow;
>> +#ifndef CONFIG_HAS_MEM_SHARING
>> +# define dom_cow NULL
>> +#endif
>>  
>>  enum XENSHARE_flags {
>>      SHARE_rw,
> 
> What is wrong with
> 
> #ifdef CONFIG_HAS_MEM_SHARING
> extern struct domain *dom_cow;
> #else
> # define dom_cow NULL
> #endif
> 
> which is how we usually express things like this?  Sure, its a tiny bit
> longer to write, but it is easier to follow.

Well, since you're the second one to ask, I'll switch, despite not agreeing
with this. Yet again some use of the C language that apparently needs
to be listed in ./CODING_STYLE as unwanted / forbidden.

Jan



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