VOP_ADVISE(9)

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(2) 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)