Re: [Qemu-devel] [PATCH 4/9] block: vhdx - log support struct and defines

[Jeff Cody <jcody@redhat.com>]

On Tue, Jul 30, 2013 at 11:15:02AM +0800, Fam Zheng wrote:
> On Wed, 07/24 13:54, Jeff Cody wrote:
> > This adds some magic number defines, and internal structure
> > definitions for VHDX log replay support.
> > 
> > Signed-off-by: Jeff Cody <jcody@redhat.com>
> > ---
> >  block/vhdx.h | 21 ++++++++++++++++++++-
> >  1 file changed, 20 insertions(+), 1 deletion(-)
> > 
> > diff --git a/block/vhdx.h b/block/vhdx.h
> > index c8d8593..2db6615 100644
> > --- a/block/vhdx.h
> > +++ b/block/vhdx.h
> > @@ -151,7 +151,10 @@ typedef struct QEMU_PACKED VHDXRegionTableEntry {
> >  
> >  
> >  /* ---- LOG ENTRY STRUCTURES ---- */
> > +#define VHDX_LOG_MIN_SIZE (1024*1024)
> > +#define VHDX_LOG_SECTOR_SIZE 4096
> >  #define VHDX_LOG_HDR_SIZE 64
> > +#define VHDX_LOG_SIGNATURE 0x65676f6c
> >  typedef struct QEMU_PACKED VHDXLogEntryHeader {
> >      uint32_t    signature;              /* "loge" in ASCII */
> >      uint32_t    checksum;               /* CRC-32C hash of the 64KB table */
> > @@ -174,7 +177,8 @@ typedef struct QEMU_PACKED VHDXLogEntryHeader {
> >  } VHDXLogEntryHeader;
> >  
> >  #define VHDX_LOG_DESC_SIZE 32
> > -
> > +#define VHDX_LOG_DESC_SIGNATURE 0x63736564
> > +#define VHDX_LOG_ZERO_SIGNATURE 0x6f72657a
> 
> Are these macros really used? I see "desc" and "zero" used to compare
> signatures.
>

They are used in the log write patch (when creating new log sectors).
Right now, we only create data sectors (nothing uses the zero sectors
yet), so only the _DESC_SIGNATURE is used.

Thanks,
Jeff