Antoine Pitrou <pit...@free.fr> added the comment: Ok, after experimenting, I now understand what the truncate() call is for.
However, your heuristic for detecting sparse files is wrong. The unit for st_blocks is undefined as per the POSIX standard, although it gives recommendations: “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.” (http://www.opengroup.org/onlinepubs/000095399/basedefs/sys/stat.h.html) Under Linux, 512 turns out to be the right multiplier (and not st_blksize): >>> f = open("foo", "wb") >>> f.write(b"x" * 4096) 4096 >>> f.truncate(16384) 16384 >>> f.close() >>> st = os.stat("foo") >>> st.st_size 16384 >>> st.st_blocks 8 >>> st.st_blocks * st.st_blksize 32768 >>> st.st_blocks * 512 4096 Also, GNU `cp` uses S_BLKSIZE rather than DEV_BSIZE when trying to detect the st_blocks unit size (both are 512 under Linux). ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue10016> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
