On Linux POSIX ACLs can be removed via rmxattr() for the
relevant system xattrs. On FreeBSD a non-trivial ACL
can be converted to one that is described by the mode with
no loss of info via combination of acl_get_file(), acl_strip_np(),
and acl_set_file(). Since there's no libc equivalent of these
ops in Linux for NFSv4 ACLs, this commit makes this less error
prone by handling entirely in ZFS. When user performs
rmxattr() vfs_setxattr() is called with value of NULL and length
of 0. Add special handling for this situation in the xattr
handler for the NFSv4 ACL so that we generate a new ACL and
zfs_acl_chmod() with the existing mode of file, then set the ACL.
Signed-off-by: Andrew Walker <awalker@ixsystems.com>
d1df3f6cab