NAME

     VOP_ADVISE — apply advice about use of file data

SYNOPSIS

     #include <sys/param.h>
     #include <sys/vnode.h>

     int
     VOP_ADVISE(struct vnode *vp, off_t start, off_t end, int advice);

DESCRIPTION

     This call applies advice for a range of a file's data.  It is used to implement the
     posix_fadvise system call.

     Its arguments are:

     vp      The vnode of the file.

     start   The start of the range of file data.

     end     The end of the range of file data.  A value of OFF_MAX indicates that the advice is
             to be applied up to the end of the file.

     advice  The type of operation to apply to the file data.  Possible values are:

             POSIX_FADV_WILLNEED  Initiate an asynchronous read of the file data if it is not
                                  already resident.

             POSIX_FADV_DONTNEED  Decrease the in-memory priority of clean file data or discard
                                  clean file data.

     If the start and end offsets are both zero, then the operation should be applied to the
     entire file.  Note that this call is advisory only and may perform the requested operation
     on a subset of the requested range (including not performing it at all) and still return
     success.

LOCKS

     The file should be unlocked on entry.

RETURN VALUES

     Zero is returned if the call is successful, otherwise an appropriate error code is returned.

ERRORS

     [EINVAL]           An invalid value was given for advice.

SEE ALSO

     vnode(9)