Re: [Qemu-devel] PATCH: Control over drive open modes for backing file

["Daniel P. Berrange" <berrange@redhat.com>]

On Thu, Jul 31, 2008 at 02:46:55PM +0100, Paul Brook wrote:
> > +#define BDRV_O_RDONLY      0x0001 /* Force read-only */
> > +#define BDRV_O_WRONLY      0x0002 /* Force writeable, no fallback */
> > +#define BDRV_O_RDWR        0x0003 /* Try writeable, fallback to read-only
> > */
> 
> This is IMHO really misleading.  Normal O_* are not bitflags. The code uses 
> these as bitflags sometimes, which means your descriptions are contradictory.

One alternative approach I considered would be to not have an explicit
flag for writable, and instead have a flag to explicitly indicate that
fallback to read-only shouldn't be attempted.

   #define BDRV_O_RDONLY            0x0001
   #define BDRV_O_NO_RO_FALLBACK    0x0002

This would probably make the patch smaller because I won't need to update
all the callers which assume flags of '0'  gives a writable file, falling
back to RO.

Other suggestions welcome too...

Daniel
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