Re: [PATCH] comments on st_blksize and f_bsize for 2.5

[Andries Brouwer <aebr@win.tue.nl>]

On Tue, Feb 18, 2003 at 08:25:40PM +0300, Hans Reiser wrote:

> Since a few applications, and the linux manpages, seem to not really 
> understand what these are for, they need comments like SUSv2 has for 
> them.  A larger discussion will be provided if requested.

> +	unsigned int	st_blksize;	/* Optimal I/O size */

> +	int f_bsize;	/* Filesystem blocksize */

Yes, discussion - I wouldnt mind seeing details.

The trivial part is st_blksize: all agree.
Quoting the man page:

       The value st_blksize gives the "preferred" blocksize
       for efficient file system I/O.  (Writing to a file in
       smaller chunks may cause an inefficient read-modify-rewrite.)

The nontrivial part is f_bsize. As far as I can see
BSD and SYSV and SUS all differ. And there are the use
in struct statfs and the use in struct statvfs that are
nonequivalent.

Maybe BSD f_iosize, f_bsize in statfs corresponds to
SYSV f_bsize, f_frsize in statfs. Linux is again a
bit different.

Andries