| Message ID | 4EAA7441.8010608@redhat.com |
|---|---|
| State | New |
| Headers | show |
Am 28.10.2011 11:22, schrieb Kevin Wolf: > Am 28.10.2011 10:15, schrieb Eric Sunshine: >> On Oct 28, 2011, at 4:00 AM, Kevin Wolf wrote: >> >>> Am 27.10.2011 18:12, schrieb Stefan Weil: >>>> Am 27.10.2011 10:53, schrieb Kevin Wolf: >>>>> Am 26.10.2011 21:51, schrieb Eric Sunshine: >>>>>> An entry in the VDI block map will hold an offset to the actual >>>>>> block if >>>>>> the block is allocated, or one of two specially-interpreted >>>>>> values if >>>>>> not allocated. Using VirtualBox terminology, value >>>>>> VDI_IMAGE_BLOCK_FREE >>>>>> (0xffffffff) represents a never-allocated block (semantically >>>>>> arbitrary >>>>>> content). VDI_IMAGE_BLOCK_ZERO (0xfffffffe) represents a >>>>>> "discarded" >>>>>> block (semantically zero-filled). block/vdi knows only about >>>>>> VDI_IMAGE_BLOCK_FREE. Teach it about VDI_IMAGE_BLOCK_ZERO. >>>>>> >>>>>> Signed-off-by: Eric Sunshine<sunshine@sunshineco.com> >>>>> Thanks, applied to the block branch. >>>>> >>>>> Kevin >>>> >>>> Kevin, I don't want to block improvements. Nevertheless >>>> I'd like to see a small modification in this patch: >>>> both #defines should be implemented without a type cast. >>>> Please change them or wait until Eric sends an update. >>>> >>>> My favorite is this: >>>> >>>> #define VDI_UNALLOCATED UINT32_MAX >>>> #define VDI_DISCARD (VDI_UNALLOCATED - 1) >>>> >>>> This would also be ok: >>>> >>>> #define VDI_UNALLOCATED 0xffffffffU >>>> #define VDI_DISCARD 0xfffffffeU >>>> >>>> Using the macro names and the definitions (with type cast) >>>> from the original VirtualBox code would also be ok. >>> I did see your comments, and I waited for the endianness thing to be >>> answered. However, how the definition of these constants is written is >>> really not a functional defect, but simply a matter of taste. It's an >>> old rule that whoever does the work also decides on the details. >>> >>> I really think it's wasting our time if we need to discuss if a type >>> cast in the constant definition is only allowed after typedefing >>> uint32_t to something else like in VBox. >>> >>> So my preferred way is to leave the patch as it is. The code is simple >>> and clear and objectively seen it won't get any better with your taste >>> applied. If Eric prefers, I can update it to use 0xffffffffU, though. >> The 0xffffffffU notation has the benefit of being explicit, whereas >> the ((uint32_t)~0) notation, taken from the VirtualBox source, is >> somewhat magical for a reader who does not perform an automatic >> ((uint32_t)~0) == 0xffffffffU conversion in his head. Consequently, >> the 0xffffffffU notation might a better choice, if it's not too much >> bother for you to amend the patch. > I'll amend it with this change: > > diff --git a/block/vdi.c b/block/vdi.c > index 25790c4..523a640 100644 > --- a/block/vdi.c > +++ b/block/vdi.c > @@ -115,10 +115,10 @@ void uuid_unparse(const uuid_t uu, char *out); > #define VDI_TEXT "<<< QEMU VM Virtual Disk Image>>>\n" > > /* A never-allocated block; semantically arbitrary content. */ > -#define VDI_UNALLOCATED ((uint32_t)~0) > +#define VDI_UNALLOCATED 0xffffffffU > > /* A discarded (no longer allocated) block; semantically zero-filled. */ > -#define VDI_DISCARDED ((uint32_t)~1) > +#define VDI_DISCARDED 0xfffffffeU > > #define VDI_IS_ALLOCATED(X) ((X)< VDI_DISCARDED) Thanks for this update. With your patch added to Eric's, I can add Acked-by: Stefan Weil <sw@weilnetz.de>
diff --git a/block/vdi.c b/block/vdi.c index 25790c4..523a640 100644 --- a/block/vdi.c +++ b/block/vdi.c @@ -115,10 +115,10 @@ void uuid_unparse(const uuid_t uu, char *out); #define VDI_TEXT "<<< QEMU VM Virtual Disk Image >>>\n" /* A never-allocated block; semantically arbitrary content. */ -#define VDI_UNALLOCATED ((uint32_t)~0) +#define VDI_UNALLOCATED 0xffffffffU /* A discarded (no longer allocated) block; semantically zero-filled. */ -#define VDI_DISCARDED ((uint32_t)~1) +#define VDI_DISCARDED 0xfffffffeU #define VDI_IS_ALLOCATED(X) ((X) < VDI_DISCARDED)