Linux 6.11: enable queue flush through queue limits

In 6.11 struct queue_limits gains a 'features' field, where, among other
things, flush and write-cache are enabled. Detect it and use it.

Along the way, the blk_queue_set_write_cache() compat wrapper gets a
little cleanup. Since both flags are alway set together, its now a
single bool. Also the very very ancient version that sets q->flush_flags
directly couldn't actually turn it off, so I've fixed that. Not that we
use it, but still.

Reviewed-by: Tony Hutter <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Rob Norris <[email protected]>
Sponsored-by: https://despairlabs.com/sponsor/
Closes openzfs#16400

config/kernel-make-request-fn.m4

@@ -58,6 +58,13 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_MAKE_REQUEST_FN], [
 		disk = blk_alloc_disk(lim, NUMA_NO_NODE);
 	])
 
+	ZFS_LINUX_TEST_SRC([blkdev_queue_limits_features], [
+		#include <linux/blkdev.h>
+	],[
+		struct queue_limits *lim = NULL;
+		lim->features = 0;
+	])
+
 	ZFS_LINUX_TEST_SRC([blk_cleanup_disk], [
 		#include <linux/blkdev.h>
 	],[
@@ -114,6 +121,20 @@ AC_DEFUN([ZFS_AC_KERNEL_MAKE_REQUEST_FN], [
 			AC_MSG_RESULT(yes)
 			AC_DEFINE([HAVE_BLK_ALLOC_DISK_2ARG], 1, [blk_alloc_disk() exists and takes 2 args])
 
+			dnl #
+			dnl # Linux 6.11 API change:
+			dnl # struct queue_limits gains a 'features' field,
+			dnl # used to set flushing options
+			dnl #
+			AC_MSG_CHECKING([whether struct queue_limits has a features field])
+			ZFS_LINUX_TEST_RESULT([blkdev_queue_limits_features], [
+				AC_MSG_RESULT(yes)
+				AC_DEFINE([HAVE_BLKDEV_QUEUE_LIMITS_FEATURES], 1,
+				    [struct queue_limits has a features field])
+			], [
+				AC_MSG_RESULT(no)
+			])
+
 			dnl #
 			dnl # 5.20 API change,
 			dnl # Removed blk_cleanup_disk(), put_disk() should be used.

include/os/linux/kernel/linux/blkdev_compat.h

@@ -57,6 +57,11 @@ blk_queue_flag_clear(unsigned int flag, struct request_queue *q)
 #endif
 
 /*
+ * 6.11 API
+ * Setting the flush flags directly is no longer possible; flush flags are set
+ * on the queue_limits structure and passed to blk_disk_alloc(). In this case
+ * we remove this function entirely.
+ *
  * 4.7 API,
  * The blk_queue_write_cache() interface has replaced blk_queue_flush()
  * interface.  However, the new interface is GPL-only thus we implement
@@ -68,31 +73,33 @@ blk_queue_flag_clear(unsigned int flag, struct request_queue *q)
  * new one is GPL-only.   Thus if the GPL-only version is detected we
  * implement our own trivial helper.
  */
+#if !defined(HAVE_BLK_ALLOC_DISK_2ARG) || \
+	!defined(HAVE_BLKDEV_QUEUE_LIMITS_FEATURES)
 static inline void
-blk_queue_set_write_cache(struct request_queue *q, bool wc, bool fua)
+blk_queue_set_write_cache(struct request_queue *q, bool on)
 {
 #if defined(HAVE_BLK_QUEUE_WRITE_CACHE_GPL_ONLY)
-	if (wc)
+	if (on) {
 		blk_queue_flag_set(QUEUE_FLAG_WC, q);
-	else
-		blk_queue_flag_clear(QUEUE_FLAG_WC, q);
-	if (fua)
 		blk_queue_flag_set(QUEUE_FLAG_FUA, q);
-	else
+	} else {
+		blk_queue_flag_clear(QUEUE_FLAG_WC, q);
 		blk_queue_flag_clear(QUEUE_FLAG_FUA, q);
+	}
 #elif defined(HAVE_BLK_QUEUE_WRITE_CACHE)
-	blk_queue_write_cache(q, wc, fua);
+	blk_queue_write_cache(q, on, on);
 #elif defined(HAVE_BLK_QUEUE_FLUSH_GPL_ONLY)
-	if (wc)
-		q->flush_flags |= REQ_FLUSH;
-	if (fua)
-		q->flush_flags |= REQ_FUA;
+	if (on)
+		q->flush_flags |= REQ_FLUSH | REQ_FUA;
+	else
+		q->flush_flags &= ~(REQ_FLUSH | REQ_FUA);
 #elif defined(HAVE_BLK_QUEUE_FLUSH)
-	blk_queue_flush(q, (wc ? REQ_FLUSH : 0) | (fua ? REQ_FUA : 0));
+	blk_queue_flush(q, on ? (REQ_FLUSH | REQ_FUA) : 0);
 #else
 #error "Unsupported kernel"
 #endif
 }
+#endif /* !HAVE_BLK_ALLOC_DISK_2ARG || !HAVE_BLKDEV_QUEUE_LIMITS_FEATURES */
 
 /*
  * Detect if a device has a write cache. Used to set the intial value for the

module/os/linux/zfs/zvol_os.c

@@ -1203,6 +1203,9 @@ zvol_queue_limits_convert(zvol_queue_limits_t *limits,
 	qlimits->max_segments = limits->zql_max_segments;
 	qlimits->max_segment_size = limits->zql_max_segment_size;
 	qlimits->io_opt = limits->zql_io_opt;
+#ifdef HAVE_BLKDEV_QUEUE_LIMITS_FEATURES
+	qlimits->features = BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA;
+#endif
 }
 #endif
 
@@ -1215,6 +1218,9 @@ zvol_queue_limits_apply(zvol_queue_limits_t *limits,
 	blk_queue_max_segments(queue, limits->zql_max_segments);
 	blk_queue_max_segment_size(queue, limits->zql_max_segment_size);
 	blk_queue_io_opt(queue, limits->zql_io_opt);
+#ifndef HAVE_BLKDEV_QUEUE_LIMITS_FEATURES
+	blk_queue_set_write_cache(queue, B_TRUE);
+#endif
 }
 
 static int
@@ -1238,6 +1244,10 @@ zvol_alloc_non_blk_mq(struct zvol_state_os *zso, zvol_queue_limits_t *limits)
 		return (1);
 	}
 
+#ifndef HAVE_BLKDEV_QUEUE_LIMITS_FEATURES
+	blk_queue_set_write_cache(zso->zvo_queue, B_TRUE);
+#endif
+
 	zso->zvo_disk = disk;
 	zso->zvo_disk->minors = ZVOL_MINORS;
 	zso->zvo_queue = zso->zvo_disk->queue;
@@ -1391,8 +1401,6 @@ zvol_alloc(dev_t dev, const char *name)
 	if (ret != 0)
 		goto out_kmem;
 
-	blk_queue_set_write_cache(zso->zvo_queue, B_TRUE, B_TRUE);
-
 	/* Limit read-ahead to a single page to prevent over-prefetching. */
 	blk_queue_set_read_ahead(zso->zvo_queue, 1);