Re: [libvirt] [PATCH] Fix sparse volume allocation reporting

On Thu, Mar 26, 2009 at 01:19:12PM +0000, Daniel P. Berrange wrote: > On Tue, Mar 24, 2009 at 03:29:21PM -0400, Cole Robinson wrote: [...] > Having read the man page again, I'm inclined to say using st_blksize > is always wrong no matter what, because it is quite clear that 'st_blocks' > is always in 512 byte units. So perhaps we might be better of doing > > #ifndef DEV_BSIZE > #define DEV_BSIZE 512 > #endif > > And then always using DEV_BSIZE. In those kind of cases I go down to the spec and it states (in the informative section though): ----------------------------------------- http://www.opengroup.org/onlinepubs/000095399/basedefs/sys/stat.h.html "The unit for the st_blocks member of the stat structure is not defined within IEEE Std 1003.1-2001. In some implementations it is 512 bytes. It may differ on a file system basis. There is no correlation between values of the st_blocks and st_blksize, and the f_bsize (from <sys/statvfs.h>) structure members. Traditionally, some implementations defined the multiplier for st_blocks in <sys/param.h> as the symbol DEV_BSIZE." ----------------------------------------- So I agree with Dan, we need to drop st_blksize in any volume size computation, and fallback to 512 if not defined, apparently only src/storage_backend.c referenced it :-) I still find the "It may differ on a file system basis" to be a bit frightening considering the sandard doesn't seems to indicate how to extract that information from the filesystem :-( , oh well ...