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int bdflush(int func, long *address);
int bdflush(int func, long data);
Note: Since Linux 2.6, this system call is deprecated and does nothing.
It is likely to disappear altogether in a future kernel release. Nowa-
days, the task performed by bdflush() is handled by the kernel pdflush
bdflush() starts, flushes, or tunes the buffer-dirty-flush daemon.
Only a privileged process (one with the CAP_SYS_ADMIN capability) may
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
The set of parameters, their values, and their valid ranges are defined
in the Linux 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 error.
EBUSY An attempt was made to enter the daemon code after another pro-
cess has already entered.
EFAULT address points outside your accessible address space.
EINVAL An attempt was made to read or write an invalid parameter num-
ber, or to write an invalid value to a parameter.
EPERM Caller does not have the CAP_SYS_ADMIN capability.
bdflush() is Linux-specific and should not be used in programs intended
to be portable.