/usr/src/zfs-0.6.5.6/config/kernel-bio-rw-discard.m4 is in zfs-dkms 0.6.5.6-0ubuntu8.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | dnl #
dnl # Interface for issuing a discard bio:
dnl # 2.6.28-2.6.35: BIO_RW_DISCARD
dnl # 2.6.36-3.x: REQ_DISCARD
dnl #
dnl # Since REQ_DISCARD is a preprocessor definition, there is no need for an
dnl # autotools check for it. Also, REQ_DISCARD existed in the request layer
dnl # until torvalds/linux@7b6d91daee5cac6402186ff224c3af39d79f4a0e unified the
dnl # request layer and bio layer flags, so it would be wrong to assume that
dnl # the APIs are mutually exclusive contrary to the typical case.
AC_DEFUN([ZFS_AC_KERNEL_BIO_RW_DISCARD], [
AC_MSG_CHECKING([whether BIO_RW_DISCARD is defined])
ZFS_LINUX_TRY_COMPILE([
#include <linux/bio.h>
],[
int flags __attribute__ ((unused));
flags = BIO_RW_DISCARD;
],[
AC_MSG_RESULT(yes)
AC_DEFINE(HAVE_BIO_RW_DISCARD, 1, [BIO_RW_DISCARD is defined])
],[
AC_MSG_RESULT(no)
])
])
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