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, 16 insertions, 170 deletions

diff --git a/config/kernel-shrink.m4 b/config/kernel-shrink.m4
index 45b4b5d4b..a40c86d5c 100644
--- a/config/kernel-shrink.m4
+++ b/config/kernel-shrink.m4
@@ -13,7 +13,6 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_SUPER_BLOCK_S_SHRINK], [
 
 		static const struct super_block
 		    sb __attribute__ ((unused)) = {
-			.s_shrink.shrink = shrink,
 			.s_shrink.seeks = DEFAULT_SEEKS,
 			.s_shrink.batch = 0,
 		};
@@ -24,101 +23,8 @@ AC_DEFUN([ZFS_AC_KERNEL_SUPER_BLOCK_S_SHRINK], [
 	AC_MSG_CHECKING([whether super_block has s_shrink])
 	ZFS_LINUX_TEST_RESULT([super_block_s_shrink], [
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_SHRINK, 1, [struct super_block has s_shrink])
-
 	],[
-		AC_MSG_RESULT(no)
-	])
-])
-
-dnl #
-dnl # 3.3 API change
-dnl # The super_block structure was changed to use an hlist_node instead
-dnl # of a list_head for the .s_instance linkage.
-dnl #
-dnl # This was done in part to resolve a race in the iterate_supers_type()
-dnl # function which was introduced in Linux 3.0 kernel.  The iterator
-dnl # was supposed to provide a safe way to call an arbitrary function on
-dnl # all super blocks of a specific type.  Unfortunately, because a
-dnl # list_head was used it was possible for iterate_supers_type() to
-dnl # get stuck spinning a super block which was just deactivated.
-dnl #
-dnl # This can occur because when the list head is removed from the
-dnl # fs_supers list it is reinitialized to point to itself.  If the
-dnl # iterate_supers_type() function happened to be processing the
-dnl # removed list_head it will get stuck spinning on that list_head.
-dnl #
-dnl # To resolve the issue for existing 3.0 - 3.2 kernels we detect when
-dnl # a list_head is used.  Then to prevent the spinning from occurring
-dnl # the .next pointer is set to the fs_supers list_head which ensures
-dnl # the iterate_supers_type() function will always terminate.
-dnl #
-AC_DEFUN([ZFS_AC_KERNEL_SRC_SUPER_BLOCK_S_INSTANCES_LIST_HEAD], [
-	ZFS_LINUX_TEST_SRC([super_block_s_instances_list_head], [
-		#include <linux/fs.h>
-	],[
-		struct super_block sb __attribute__ ((unused));
-		INIT_LIST_HEAD(&sb.s_instances);
-	])
-])
-
-AC_DEFUN([ZFS_AC_KERNEL_SUPER_BLOCK_S_INSTANCES_LIST_HEAD], [
-	AC_MSG_CHECKING([whether super_block has s_instances list_head])
-	ZFS_LINUX_TEST_RESULT([super_block_s_instances_list_head], [
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_S_INSTANCES_LIST_HEAD, 1,
-		    [struct super_block has s_instances list_head])
-	],[
-		AC_MSG_RESULT(no)
-	])
-])
-
-AC_DEFUN([ZFS_AC_KERNEL_SRC_NR_CACHED_OBJECTS], [
-	ZFS_LINUX_TEST_SRC([nr_cached_objects], [
-		#include <linux/fs.h>
-
-		int nr_cached_objects(struct super_block *sb) { return 0; }
-
-		static const struct super_operations
-		    sops __attribute__ ((unused)) = {
-			.nr_cached_objects = nr_cached_objects,
-		};
-	],[])
-])
-
-AC_DEFUN([ZFS_AC_KERNEL_NR_CACHED_OBJECTS], [
-	AC_MSG_CHECKING([whether sops->nr_cached_objects() exists])
-	ZFS_LINUX_TEST_RESULT([nr_cached_objects], [
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_NR_CACHED_OBJECTS, 1,
-		    [sops->nr_cached_objects() exists])
-	],[
-		AC_MSG_RESULT(no)
-	])
-])
-
-AC_DEFUN([ZFS_AC_KERNEL_SRC_FREE_CACHED_OBJECTS], [
-	ZFS_LINUX_TEST_SRC([free_cached_objects], [
-		#include <linux/fs.h>
-
-		void free_cached_objects(struct super_block *sb, int x)
-		    { return; }
-
-		static const struct super_operations
-		    sops __attribute__ ((unused)) = {
-			.free_cached_objects = free_cached_objects,
-		};
-	],[])
-])
-
-AC_DEFUN([ZFS_AC_KERNEL_FREE_CACHED_OBJECTS], [
-	AC_MSG_CHECKING([whether sops->free_cached_objects() exists])
-	ZFS_LINUX_TEST_RESULT([free_cached_objects], [
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_FREE_CACHED_OBJECTS, 1,
-		    [sops->free_cached_objects() exists])
-	],[
-		AC_MSG_RESULT(no)
+		ZFS_LINUX_TEST_ERROR([sb->s_shrink()])
 	])
 ])
 
@@ -149,29 +55,6 @@ AC_DEFUN([ZFS_AC_KERNEL_SHRINK_CONTROL_HAS_NID], [
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER_CALLBACK], [
-	ZFS_LINUX_TEST_SRC([shrinker_cb_2arg], [
-		#include <linux/mm.h>
-		int shrinker_cb(int nr_to_scan, gfp_t gfp_mask) { return 0; }
-	],[
-		struct shrinker cache_shrinker = {
-			.shrink = shrinker_cb,
-			.seeks = DEFAULT_SEEKS,
-		};
-		register_shrinker(&cache_shrinker);
-	])
-
-	ZFS_LINUX_TEST_SRC([shrinker_cb_3arg], [
-		#include <linux/mm.h>
-		int shrinker_cb(struct shrinker *shrink, int nr_to_scan,
-		    gfp_t gfp_mask) { return 0; }
-	],[
-		struct shrinker cache_shrinker = {
-			.shrink = shrinker_cb,
-			.seeks = DEFAULT_SEEKS,
-		};
-		register_shrinker(&cache_shrinker);
-	])
-
 	ZFS_LINUX_TEST_SRC([shrinker_cb_shrink_control], [
 		#include <linux/mm.h>
 		int shrinker_cb(struct shrinker *shrink,
@@ -200,60 +83,29 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER_CALLBACK], [
 
 AC_DEFUN([ZFS_AC_KERNEL_SHRINKER_CALLBACK],[
 	dnl #
-	dnl # 2.6.23 to 2.6.34 API change
-	dnl # ->shrink(int nr_to_scan, gfp_t gfp_mask)
+	dnl # 3.0 - 3.11 API change
+	dnl # ->shrink(struct shrinker *, struct shrink_control *sc)
 	dnl #
-	AC_MSG_CHECKING([whether old 2-argument shrinker exists])
-	ZFS_LINUX_TEST_RESULT([shrinker_cb_2arg], [
+	AC_MSG_CHECKING([whether new 2-argument shrinker exists])
+	ZFS_LINUX_TEST_RESULT([shrinker_cb_shrink_control], [
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_2ARGS_OLD_SHRINKER_CALLBACK, 1,
-		    [old shrinker callback wants 2 args])
+		AC_DEFINE(HAVE_SINGLE_SHRINKER_CALLBACK, 1,
+		    [new shrinker callback wants 2 args])
 	],[
 		AC_MSG_RESULT(no)
 
 		dnl #
-		dnl # 2.6.35 - 2.6.39 API change
-		dnl # ->shrink(struct shrinker *,
-		dnl #          int nr_to_scan, gfp_t gfp_mask)
+		dnl # 3.12 API change,
+		dnl # ->shrink() is logically split in to
+		dnl # ->count_objects() and ->scan_objects()
 		dnl #
-		AC_MSG_CHECKING([whether old 3-argument shrinker exists])
-		ZFS_LINUX_TEST_RESULT([shrinker_cb_3arg], [
+		AC_MSG_CHECKING([whether ->count_objects callback exists])
+		ZFS_LINUX_TEST_RESULT([shrinker_cb_shrink_control_split], [
 			AC_MSG_RESULT(yes)
-			AC_DEFINE(HAVE_3ARGS_SHRINKER_CALLBACK, 1,
-				[old shrinker callback wants 3 args])
+			AC_DEFINE(HAVE_SPLIT_SHRINKER_CALLBACK, 1,
+			    [->count_objects exists])
 		],[
-			AC_MSG_RESULT(no)
-
-			dnl #
-			dnl # 3.0 - 3.11 API change
-			dnl # ->shrink(struct shrinker *,
-			dnl #          struct shrink_control *sc)
-			dnl #
-			AC_MSG_CHECKING(
-			    [whether new 2-argument shrinker exists])
-			ZFS_LINUX_TEST_RESULT([shrinker_cb_shrink_control], [
-				AC_MSG_RESULT(yes)
-				AC_DEFINE(HAVE_2ARGS_NEW_SHRINKER_CALLBACK, 1,
-					[new shrinker callback wants 2 args])
-			],[
-				AC_MSG_RESULT(no)
-
-				dnl #
-				dnl # 3.12 API change,
-				dnl # ->shrink() is logically split in to
-				dnl # ->count_objects() and ->scan_objects()
-				dnl #
-				AC_MSG_CHECKING(
-				    [whether ->count_objects callback exists])
-				ZFS_LINUX_TEST_RESULT(
-				    [shrinker_cb_shrink_control_split], [
-					AC_MSG_RESULT(yes)
-					AC_DEFINE(HAVE_SPLIT_SHRINKER_CALLBACK,
-						1, [->count_objects exists])
-				],[
-					ZFS_LINUX_TEST_ERROR([shrinker])
-				])
-			])
+			ZFS_LINUX_TEST_ERROR([shrinker])
 		])
 	])
 ])
@@ -280,15 +132,12 @@ AC_DEFUN([ZFS_AC_KERNEL_SHRINK_CONTROL_STRUCT], [
 		AC_DEFINE(HAVE_SHRINK_CONTROL_STRUCT, 1,
 		    [struct shrink_control exists])
 	],[
-		AC_MSG_RESULT(no)
+		ZFS_LINUX_TEST_ERROR([shrink_control])
 	])
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER], [
 	ZFS_AC_KERNEL_SRC_SUPER_BLOCK_S_SHRINK
-	ZFS_AC_KERNEL_SRC_SUPER_BLOCK_S_INSTANCES_LIST_HEAD
-	ZFS_AC_KERNEL_SRC_NR_CACHED_OBJECTS
-	ZFS_AC_KERNEL_SRC_FREE_CACHED_OBJECTS
 	ZFS_AC_KERNEL_SRC_SHRINK_CONTROL_HAS_NID
 	ZFS_AC_KERNEL_SRC_SHRINKER_CALLBACK
 	ZFS_AC_KERNEL_SRC_SHRINK_CONTROL_STRUCT
@@ -296,9 +145,6 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_SHRINKER], [
 
 AC_DEFUN([ZFS_AC_KERNEL_SHRINKER], [
 	ZFS_AC_KERNEL_SUPER_BLOCK_S_SHRINK
-	ZFS_AC_KERNEL_SUPER_BLOCK_S_INSTANCES_LIST_HEAD
-	ZFS_AC_KERNEL_NR_CACHED_OBJECTS
-	ZFS_AC_KERNEL_FREE_CACHED_OBJECTS
 	ZFS_AC_KERNEL_SHRINK_CONTROL_HAS_NID
 	ZFS_AC_KERNEL_SHRINKER_CALLBACK
 	ZFS_AC_KERNEL_SHRINK_CONTROL_STRUCT