getbsize man page
getbsize — get preferred block size
getbsize(int *headerlenp, long *blocksizep);
The getbsize() function returns a preferred block size for reporting by system utilities df(1), du(1), ls(1) and systat(1), based on the value of the BLOCKSIZE environment variable. 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.
Valid values of 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 getbsize() produces a warning message.
The getbsize() function returns a pointer to a null-terminated string describing the block size, something like “1K-blocks”. The memory referenced by headerlenp is filled in with the length of the string (not including the terminating null). The memory referenced by blocksizep is filled in with block size, in bytes.
df(1), du(1), ls(1), systat(1), environ(7)
The getbsize() function first appeared in 4.4BSD.