Re: Bug#294206: stat(1) unclear about block size

[Michael Stone]

On Tue, Feb 08, 2005 at 03:39:05PM +0000, James Youngman wrote:
> No.    The POSIX standard (in a non-normative section) says :-
>
> | 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.
>
> I think almost all systems use 512 byte units.

Note where it says "some implementations"? You're diving heavily into
implementation-specific logic, and making unfounded assumptions. The
part where it says "There is no correlation between values of the
st_blocks and st_blksize, and the f_bsize" goes with "The unit for the
st_blocks member of the stat structure is not defined within IEEE Std
1003.1-2001". IOW, POSIX doesn't define any such relationship. A
particular implementation *may* define such a relationship (and linux
has). On other platforms the st_blocks unit could be constant and the
st_blksize might actually be a suggestion to applications as to what the
most efficient I/O size is (e.g., the size of a disk stripe).

Mike Stone