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author Karl Berry <karl@freefriends.org>
date Fri, 16 Aug 2013 06:32:22 -0700
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@node stat-size
@section stat-size

The @code{stat-size} module provides a small number of macros
intended for interpreting the file size information in an instance of
@code{struct stat}.

@c We deliberately don't document DEV_BSIZE (it looks to James
@c Youngman as if the ST_NBLOCKSIZE macro should be used instead).

@findex ST_NBLOCKS
@findex ST_NBLOCKSIZE
@cindex block size
On POSIX systems, the @code{st_blocks} member of @code{struct stat}
contains the number of disk blocks occupied by a file.  The
@code{ST_NBLOCKS} macro is used to estimate this quantity on systems
which don't actually have @code{st_blocks}.  Each of these blocks
contains @code{ST_NBLOCKSIZE} bytes.

@findex ST_BLKSIZE
The value of @code{ST_NBLOCKSIZE} is often quite small, small enough
that performing I/O in chunks that size would be inefficient.
@code{ST_BLKSIZE} is the I/O block size recommended for I/O to this
file.  This is not guaranteed to give optimum performance, but it
should be reasonably efficient.