RE: [Xen-devel] __RING_SIZE() macro not aconstant when compiling under windows

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> __RING_SIZE() isn't necessarily plain constant - it does calculations.
In
> practice, these can typically be evaluated at compile time (if sz is a
> constant).  I don't know the C spec well enough to know if it's
> appropriate
> to reject this...
> 
> But __RING_SIZE isn't (as far as I know) actually used anywhere to
size
> arrays?  It's used internally by the other macros in ring.h to set up
> various
> book keeping.  So I'm not sure that you should necessarily need to use
the
> macro this way...?

In linux-2.6-xen-sparse/drivers/xen/blkfront/block.h is this:

"
#define BLK_RING_SIZE __RING_SIZE((blkif_sring_t *)0, PAGE_SIZE)

...

struct blkfront_info
{
  ...
  struct blk_shadow shadow[BLK_RING_SIZE];
  ...
"

Which I have to implement in some fashion to get the vbd working under
Windows. For now, i'm just using a pointer instead of an array and am
allocating the memory at runtime.

I've almost got vbd reads going, but I'm pretty sure that there's
currently more race conditions than I can poke a stick at... it seems to
go okay until I put a partition table on the virtual disk...

Btw, can anyone explain why the blk_shadow struct has a
'blkif_request_t' in it, when it only uses the id field?

Also, in the same blk_shadow struct, the 'request' field is of type
unsigned long, but is treated as a pointer to a 'struct request'...
seems wrong to me.

Thanks

James


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