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       bdflush - start, flush, or tune buffer-dirty-flush daemon


       #include <sys/kdaemon.h>

       int bdflush(int func, long *address);
       int bdflush(int func, long data);


       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

       The set of parameters, their values, and their valid 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 error.


       EBUSY  An  attempt  was  made  to  enter  the daemon code after another
              process has already entered.

       EFAULT address points outside your accessible address space.

       EINVAL An attempt was made  to  read  or  write  an  invalid  parameter
              number, 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.


       fsync(2), sync(2), sync(8), update(8)


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