xref: /freebsd/lib/libc/gen/getbsize.3 (revision dc36d6f9bb1753f3808552f3afd30eda9a7b206a)

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.Dd June 11, 2017
.Dt GETBSIZE 3
.Os
.Sh NAME
.Nm getbsize
.Nd get preferred block size
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft char *
.Fn getbsize "int *headerlenp" "long *blocksizep"
.Sh DESCRIPTION
The
.Fn getbsize
function returns a preferred block size for reporting by system utilities
.Xr df 1 ,
.Xr du 1
and
.Xr ls 1 ,
based on the value of the
.Ev BLOCKSIZE
environment variable.
.Ev BLOCKSIZE
may be specified directly in bytes, or in multiples of a kilobyte by
specifying a number followed by ``K'' or ``k'', in multiples of a
megabyte by specifying a number followed by ``M'' or ``m'' or in
multiples of a gigabyte by specifying a number followed by ``G'' or
``g''.
Multiples must be integers.
.Pp
Valid values of
.Ev BLOCKSIZE
are 512 bytes to 1 gigabyte.
Sizes less than 512 bytes are rounded up to 512 bytes, and sizes
greater than 1 GB are rounded down to 1 GB.
In each case
.Fn getbsize
produces a warning message via
.Xr warnx 3 .
.Pp
The
.Fn getbsize
function returns a pointer to a null-terminated string describing
the block size, something like
.Dq 1K-blocks .
The memory referenced by
.Fa headerlenp
is filled in with the length of the string (not including the
terminating null).
The memory referenced by
.Fa blocksizep
is filled in with block size, in bytes.
.Sh SEE ALSO
.Xr df 1 ,
.Xr du 1 ,
.Xr ls 1 ,
.Xr systat 1 ,
.Xr environ 7
.Sh HISTORY
The
.Fn getbsize
function first appeared in
.Bx 4.4 .