Linux compat: Minimum kernel version 3.10

Increase the minimum supported kernel version from 2.6.32 to 3.10.
This removes support for the following Linux enterprise distributions.

    Distribution     | Kernel | End of Life
    ---------------- | ------ | -------------
    Ubuntu 12.04 LTS | 3.2    | Apr 28, 2017
    SLES 11          | 3.0    | Mar 32, 2019
    RHEL / CentOS 6  | 2.6.32 | Nov 30, 2020

The following changes were made as part of removing support.

* Updated `configure` to enforce a minimum kernel version as
  specified in the META file (Linux-Minimum: 3.10).

    configure: error:
        *** Cannot build against kernel version 2.6.32.
        *** The minimum supported kernel version is 3.10.

* Removed all `configure` kABI checks and matching C code for
  interfaces which solely predate the Linux 3.10 kernel.

* Updated all `configure` kABI checks to fail when an interface is
  missing which was in the 3.10 kernel up to the latest 5.1 kernel.
  Removed the HAVE_* preprocessor defines for these checks and
  updated the code to unconditionally use the verified interface.

* Inverted the detection logic in several kABI checks to match
  the new interface as it appears in 3.10 and newer and not the
  legacy interface.

* Consolidated the following checks in to individual files. Due
  the large number of changes in the checks it made sense to handle
  this now.  It would be desirable to group other related checks in
  the same fashion, but this as left as future work.

  - config/kernel-blkdev.m4 - Block device kABI checks
  - config/kernel-blk-queue.m4 - Block queue kABI checks
  - config/kernel-bio.m4 - Bio interface kABI checks

* Removed the kABI checks for sops->nr_cached_objects() and
  sops->free_cached_objects().  These interfaces are currently unused.

Signed-off-by: Brian Behlendorf <[email protected]>
Closes #9566 

1 files changed, 0 insertions, 30 deletions

diff --git a/config/kernel-bio-rw-discard.m4 b/config/kernel-bio-rw-discard.m4
deleted file mode 100644
index 34a89279c..000000000
--- a/config/kernel-bio-rw-discard.m4
+++ /dev/null
@@ -1,30 +0,0 @@
-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 #
-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.
-dnl #
-AC_DEFUN([ZFS_AC_KERNEL_SRC_BIO_RW_DISCARD], [
-	ZFS_LINUX_TEST_SRC([bio_rw_discard], [
-		#include <linux/bio.h>
-	],[
-		int flags __attribute__ ((unused));
-		flags = BIO_RW_DISCARD;
-	])
-])
-
-AC_DEFUN([ZFS_AC_KERNEL_BIO_RW_DISCARD], [
-	AC_MSG_CHECKING([whether BIO_RW_DISCARD is defined])
-	ZFS_LINUX_TEST_RESULT([bio_rw_discard], [
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_BIO_RW_DISCARD, 1, [BIO_RW_DISCARD is defined])
-	],[
-		AC_MSG_RESULT(no)
-	])
-])