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

Daniel P. Berrange wrote: > On Thu, Mar 26, 2009 at 05:55:00PM +0100, Daniel Veillard wrote: >> 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 ... > I guess if we come across a filesystem where it is not 512, then someone > will have created an ioctl() or equivalent to let us find out the true > value. Failing that, relying on 512 seems like a good plan. > > Daniel Okay, updated patch attached.