bdflush() starts, flushes, or tunes the buffer-dirty-flush daemon.
Only a privileged process (one with the
CAP_SYS_ADMIN capability) may call
bdflush().
If
func is negative or 0, and no daemon has been started, then
bdflush() enters the daemon code and never returns.
If
func is 1,
some dirty buffers are written to disk.
If
func is 2 or more and is even (low bit is 0), then
address is the address of a long word,
and the tuning parameter numbered
(func-2)/2 is returned to the caller in that address.
If
func is 3 or more and is odd (low bit is 1), then
data is a long word,
and the kernel sets tuning parameter numbered
(func-3)/2 to that value.
The set of parameters, their values, and their legal ranges
are defined in the kernel source file
fs/buffer.c.
