Re: [Xen-devel] [PATCH 3/4] xen: make start_info x86 specific.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.02.13 at 15:46, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Thu, 2013-02-14 at 14:43 +0000, Jan Beulich wrote:
>> >>> On 14.02.13 at 15:16, Ian Campbell <ian.campbell@xxxxxxxxxx> wrote:
>> > Most of this struct is PV MMU specific and it is not used on ARM at all.
>> 
>> I'm not convinced this is the right move.
>> 
>> > --- a/xen/include/public/xen.h
>> > +++ b/xen/include/public/xen.h
>> > @@ -706,79 +706,6 @@ typedef struct shared_info shared_info_t;
>> >   *     extended by an extra 4MB to ensure this.
>> >   */
>> >  
>> > -#define MAX_GUEST_CMDLINE 1024
>> > -struct start_info {
>> > -    /* THE FOLLOWING ARE FILLED IN BOTH ON INITIAL BOOT AND ON RESUME.    
> */
>> > -    char magic[32];             /* "xen-<version>-<platform>".            
>> > */
>> > -    unsigned long nr_pages;     /* Total pages allocated to this domain.  
> */
>> > -    unsigned long shared_info;  /* MACHINE address of shared info struct. 
> */
>> > -    uint32_t flags;             /* SIF_xxx flags.                         
> */
>> > -    xen_pfn_t store_mfn;        /* MACHINE page number of shared page.    
> */
>> > -    uint32_t store_evtchn;      /* Event channel for store communication. 
> */
>> > -    union {
>> > -        struct {
>> > -            xen_pfn_t mfn;      /* MACHINE page number of console page.   
> */
>> > -            uint32_t  evtchn;   /* Event channel for console page.        
> */
>> > -        } domU;
>> > -        struct {
>> > -            uint32_t info_off;  /* Offset of console_info struct.         
> */
>> > -            uint32_t info_size; /* Size of console_info struct from 
> start.*/
>> > -        } dom0;
>> > -    } console;
>> 
>> What is PV MMU related up to here?
> 
> Hrm, perhaps categorising this as PV MMU was a mistake on my part.
> 
> These are all unused on ARM in terms of the hypervisor ABI since it uses
> HVM like mechanisms for those which are appropriate and doesn't use a
> bunch of the others at all.

But nothing here makes this structure x86 specific, so I'd really like
to keep it that way. If ARM doesn't use the structure at all, then
I don't see the point in removing it from the common headers. If
part of it (the flags come to mind) are being used by ARM, let's
find a reasonable abstraction so that ARM doesn't need to carry
useless baggage (e.g. a XEN_ARCH_HVM_ONLY #define).

Jan


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