On Wed, Aug 02, 2006 at 05:04:53AM +1000, Peter Jeremy wrote: > On Tue, 2006-Aug-01 12:51:32 -0500, Eric Anderson wrote: > >string of zeros larger than the block size, or it needs to 'do the right > >thing' and determine if it's sparse or not. > > You can do this by comparing stat.st_size with stat.st_blocks - a > sparse file will have fewer blocks than its size requires. What you > can't do is accurately determine where the holes are. > > Note that st_blksize is not nessarily the allocation blocksize and > therefore is unrelated to the size of holes in the filesystem. Also, > on FreeBSD, the designation of "optimal" is a misnomer and I/O > operations should be much larger than this for optimal efficiency.
True, but I've not seen the case where the following is not true: The filesystem's block size (i.e. 8x fragment size) in UFS an integer multiple of st_blksize. My previously-posted example would work just fine. I guess a better solution would be to check every 512-byte chunk and seek if zero. It's up to the underlying filesystem to implement this as a sparse file, if that filesystem supports such a thing. -- Rick C. Petty _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
