4.10 compat - BIO flag changes and others

[bio] The req_op enum was changed to req_opf.  Update the "Linux 4.8 API"
autotools checks to use an int to determine whether the various REQ_OP
values are defined.  This should work properly on kernels >= 4.8.

[bio] bio_set_op_attrs() is now an inline function and can't be detected
with #ifdef.  Add a configure check to determine whether bio_set_op_attrs()
is defined.  Move the local definition of it from vdev_disk.c to
blkdev_compat.h for consistency with other related compability shims.

[bio] The read/write flags and their modifiers, including WRITE_FLUSH,
WRITE_FUA and WRITE_FLUSH_FUA have been removed from fs.h.  Add the new
bio_set_flush() compatibility wrapper to replace VDEV_WRITE_FLUSH_FUA
and set the flags appropriately for each supported kernel version.

[vfs] The generic_readlink() function has been made static.  If .readlink
in inode_operations is NULL, generic_readlink() is used.

[zol typo] Completely unrelated to 4.10 compat, fix a typo in the check
for REQ_OP_SECURE_ERASE so that the proper macro is defined:

    s/HAVE_REQ_OP_SECURE_DISCARD/HAVE_REQ_OP_SECURE_ERASE/

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
Closes #5499

config/kernel-bio-op.m4

@@ -10,7 +10,7 @@ AC_DEFUN([ZFS_AC_KERNEL_REQ_OP_DISCARD], [
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blk_types.h>
 	],[
-		enum req_op op __attribute__ ((unused)) = REQ_OP_DISCARD;
+		int op __attribute__ ((unused)) = REQ_OP_DISCARD;
 	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_REQ_OP_DISCARD, 1,
@@ -25,10 +25,10 @@ AC_DEFUN([ZFS_AC_KERNEL_REQ_OP_SECURE_ERASE], [
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blk_types.h>
 	],[
-		enum req_op op __attribute__ ((unused)) = REQ_OP_SECURE_ERASE;
+		int op __attribute__ ((unused)) = REQ_OP_SECURE_ERASE;
 	],[
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_REQ_OP_SECURE_DISCARD, 1,
+		AC_DEFINE(HAVE_REQ_OP_SECURE_ERASE, 1,
 		    [REQ_OP_SECURE_ERASE is defined])
 	],[
 		AC_MSG_RESULT(no)
@@ -41,7 +41,7 @@ AC_DEFUN([ZFS_AC_KERNEL_REQ_OP_FLUSH], [
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blk_types.h>
 	],[
-		enum req_op op __attribute__ ((unused)) = REQ_OP_FLUSH;
+		int op __attribute__ ((unused)) = REQ_OP_FLUSH;
 	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_REQ_OP_FLUSH, 1,
@@ -65,3 +65,20 @@ AC_DEFUN([ZFS_AC_KERNEL_BIO_BI_OPF], [
 		AC_MSG_RESULT(no)
 	])
 ])
+
+AC_DEFUN([ZFS_AC_KERNEL_HAVE_BIO_SET_OP_ATTRS], [
+	AC_MSG_CHECKING([whether bio_set_op_attrs is available])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/blk_types.h>
+	],[
+		struct bio *bio __attribute__ ((unused)) = NULL;
+
+		bio_set_op_attrs(bio, 0, 0);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_BIO_SET_OP_ATTRS, 1,
+		    [bio_set_op_attrs is available])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])

config/kernel-generic_readlink.m4

@@ -0,0 +1,22 @@
+dnl #
+dnl # 4.10 API
+dnl #
+dnl # NULL inode_operations.readlink implies generic_readlink(), which
+dnl # has been made static.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_GENERIC_READLINK_GLOBAL], [
+	AC_MSG_CHECKING([whether generic_readlink is global])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/fs.h>
+	],[
+		int i __attribute__ ((unused));
+
+		i = generic_readlink(NULL, NULL, 0);
+	],[
+		AC_MSG_RESULT([yes])
+		AC_DEFINE(HAVE_GENERIC_READLINK, 1,
+		          [generic_readlink is global])
+	],[
+		AC_MSG_RESULT([no])
+	])
+])

config/kernel.m4

@@ -37,6 +37,8 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_BLK_QUEUE_HAVE_BLK_PLUG
 	ZFS_AC_KERNEL_GET_DISK_RO
 	ZFS_AC_KERNEL_GET_GENDISK
+	ZFS_AC_KERNEL_HAVE_BIO_SET_OP_ATTRS
+	ZFS_AC_KERNEL_GENERIC_READLINK_GLOBAL
 	ZFS_AC_KERNEL_DISCARD_GRANULARITY
 	ZFS_AC_KERNEL_CONST_XATTR_HANDLER
 	ZFS_AC_KERNEL_XATTR_HANDLER_NAME

include/linux/blkdev_compat.h

@@ -303,20 +303,59 @@ bio_set_flags_failfast(struct block_device *bdev, int *flags)
 #endif /* HAVE_BDEV_LOGICAL_BLOCK_SIZE */
 #endif /* HAVE_BDEV_PHYSICAL_BLOCK_SIZE */
 
+#ifndef HAVE_BIO_SET_OP_ATTRS
 /*
- * 2.6.37 API change
+ * Kernels without bio_set_op_attrs use bi_rw for the bio flags.
- * The WRITE_FLUSH, WRITE_FUA, and WRITE_FLUSH_FUA flags have been
- * introduced as a replacement for WRITE_BARRIER.  This was done to
- * allow richer semantics to be expressed to the block layer.  It is
- * the block layers responsibility to choose the correct way to
- * implement these semantics.
  */
-#ifdef WRITE_FLUSH_FUA
+static inline void
-#define	VDEV_WRITE_FLUSH_FUA		WRITE_FLUSH_FUA
+bio_set_op_attrs(struct bio *bio, unsigned rw, unsigned flags)
-#else
+{
-#define	VDEV_WRITE_FLUSH_FUA		WRITE_BARRIER
+	bio->bi_rw |= rw | flags;
+}
 #endif
 
+/*
+ * bio_set_flush - Set the appropriate flags in a bio to guarantee
+ * data are on non-volatile media on completion.
+ *
+ * 2.6.X - 2.6.36 API,
+ *   WRITE_BARRIER - Tells the block layer to commit all previously submitted
+ *   writes to stable storage before this one is started and that the current
+ *   write is on stable storage upon completion.  Also prevents reordering
+ *   on both sides of the current operation.
+ *
+ * 2.6.37 - 4.8 API,
+ *   Introduce  WRITE_FLUSH, WRITE_FUA, and WRITE_FLUSH_FUA flags as a
+ *   replacement for WRITE_BARRIER to allow expressing richer semantics
+ *   to the block layer.  It's up to the block layer to implement the
+ *   semantics correctly. Use the WRITE_FLUSH_FUA flag combination.
+ *
+ * 4.8 - 4.9 API,
+ *   REQ_FLUSH was renamed to REQ_PREFLUSH.  For consistency with previous
+ *   ZoL releases, prefer the WRITE_FLUSH_FUA flag set if it's available.
+ *
+ * 4.10 API,
+ *   The read/write flags and their modifiers, including WRITE_FLUSH,
+ *   WRITE_FUA and WRITE_FLUSH_FUA were removed from fs.h in
+ *   torvalds/linux@70fd7614 and replaced by direct flag modification
+ *   of the REQ_ flags in bio->bi_opf.  Use REQ_PREFLUSH.
+ */
+static inline void
+bio_set_flush(struct bio *bio)
+{
+#if defined(WRITE_BARRIER)	/* < 2.6.37 */
+	bio_set_op_attrs(bio, 0, WRITE_BARRIER);
+#elif defined(WRITE_FLUSH_FUA)	/* >= 2.6.37 and <= 4.9 */
+	bio_set_op_attrs(bio, 0, WRITE_FLUSH_FUA);
+#elif defined(REQ_PREFLUSH)	/* >= 4.10 */
+	bio_set_op_attrs(bio, 0, REQ_PREFLUSH);
+#else
+#error	"Allowing the build will cause bio_set_flush requests to be ignored."
+	"Please file an issue report at: "
+	"https://github.com/zfsonlinux/zfs/issues/new"
+#endif
+}
+
 /*
  * 4.8 - 4.x API,
  *   REQ_OP_FLUSH

module/zfs/vdev_disk.c

@@ -488,11 +488,6 @@ bio_map_abd_off(struct bio *bio, abd_t *abd, unsigned int size, size_t off)
 	return (abd_scatter_bio_map_off(bio, abd, size, off));
 }
 
-#ifndef bio_set_op_attrs
-#define	bio_set_op_attrs(bio, rw, flags) \
-	do { (bio)->bi_rw |= (rw)|(flags); } while (0)
-#endif
-
 static inline void
 vdev_submit_bio_impl(struct bio *bio)
 {
@@ -659,7 +654,7 @@ vdev_disk_io_flush(struct block_device *bdev, zio_t *zio)
 	bio->bi_end_io = vdev_disk_io_flush_completion;
 	bio->bi_private = zio;
 	bio->bi_bdev = bdev;
-	bio_set_op_attrs(bio, 0, VDEV_WRITE_FLUSH_FUA);
+	bio_set_flush(bio);
 	vdev_submit_bio(bio);
 	invalidate_bdev(bdev);
 

module/zfs/zpl_inode.c

@@ -770,7 +770,9 @@ const struct inode_operations zpl_dir_inode_operations = {
 };
 
 const struct inode_operations zpl_symlink_inode_operations = {
+#ifdef HAVE_GENERIC_READLINK
 	.readlink	= generic_readlink,
+#endif
 #if defined(HAVE_GET_LINK_DELAYED) || defined(HAVE_GET_LINK_COOKIE)
 	.get_link	= zpl_get_link,
 #elif defined(HAVE_FOLLOW_LINK_COOKIE) || defined(HAVE_FOLLOW_LINK_NAMEIDATA)