This call implements the logic for the
discretionary file security model
with POSIX.1e ACL extensions.
It accepts the vnodes type
access ACL for the file
desired access mode
and an optional call-by-reference
pointer returning whether or not
privilege was required for successful evaluation of the call; the
pointer may be set to
by the caller in order not to be informed of
privilege information, or it may point to an integer that will be set to
1 if privilege is used, and 0 otherwise.
This call is intended to support implementations of
which will use their own access methods to retrieve the vnode properties,
and then invoke
in order to perform the actual check.
may choose to implement additional security mechanisms whose results will
be composed with the return value.
The algorithm used by
is based on the POSIX.1e ACL evaluation algorithm.
The algorithm selects a
entry from the access ACL, which may
then be composed with an available ACL mask entry, providing
Once appropriate protections are selected for the current credential,
the requested access mode, in combination with the vnode type, will be
compared with the discretionary rights available for the credential.
If the rights granted by discretionary protections are insufficient,
then super-user privilege, if available for the credential, will also be