bdflush - start, flush, or tune buffer-dirty-flush daemon
int bdflush(int func, long *address);
int bdflush(int func, long data);
bdflush starts, flushes, or tunes the buffer-dirty-flush
daemon. Only the super-user 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 param-
eter numbered (func-2)/2 is returned to the caller in that
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.
If func is negative or 0 and the daemon successfully starts,
bdflush never returns. Otherwise, the return value is 0 on
success and -1 on failure, with errno set to indicate the
EPERM Caller is not super-user.
EFAULT address points outside your accessible address
EBUSY An attempt was made to enter the daemon code after
another process has already entered.
EINVAL An attempt was made to read or write an invalid
parameter number, or to write an invalid value to a
bdflush is Linux specific and should not be used in programs
intended to be portable.
fsync(2), sync(2), update(8), sync(8).