zio: remove io_cmd and DKIOCFLUSHWRITECACHE

There's no other options, so we can just always assume its a flush.

Includes some light refactoring where a switch statement was doing
control flow that no longer works.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #16064

10 files changed, 106 insertions, 157 deletions

diff --git a/include/os/linux/zfs/sys/trace_common.h b/include/os/linux/zfs/sys/trace_common.h
index 3d4b1920d598..6ffa57c86418 100644
--- a/include/os/linux/zfs/sys/trace_common.h
+++ b/include/os/linux/zfs/sys/trace_common.h
@@ -31,7 +31,6 @@
 /* ZIO macros */
 #define	ZIO_TP_STRUCT_ENTRY						\
 		__field(zio_type_t,		zio_type)		\
-		__field(int,			zio_cmd)		\
 		__field(zio_priority_t,		zio_priority)		\
 		__field(uint64_t,		zio_size)		\
 		__field(uint64_t,		zio_orig_size)		\
@@ -61,7 +60,6 @@
 
 #define	ZIO_TP_FAST_ASSIGN						    \
 		__entry->zio_type		= zio->io_type;		    \
-		__entry->zio_cmd		= zio->io_cmd;		    \
 		__entry->zio_priority		= zio->io_priority;	    \
 		__entry->zio_size		= zio->io_size;		    \
 		__entry->zio_orig_size		= zio->io_orig_size;	    \
@@ -90,7 +88,7 @@
 		__entry->zp_dedup_verify	= zio->io_prop.zp_dedup_verify;
 
 #define	ZIO_TP_PRINTK_FMT						\
-	"zio { type %u cmd %i prio %u size %llu orig_size %llu "	\
+	"zio { type %u prio %u size %llu orig_size %llu "		\
 	"offset %llu timestamp %llu delta %llu delay %llu "		\
 	"flags 0x%llx stage 0x%x pipeline 0x%x orig_flags 0x%llx "	\
 	"orig_stage 0x%x orig_pipeline 0x%x reexecute %u "		\
@@ -98,7 +96,7 @@
 	"type %u level %u copies %u dedup %u dedup_verify %u nopwrite %u } }"
 
 #define	ZIO_TP_PRINTK_ARGS						\
-	__entry->zio_type, __entry->zio_cmd, __entry->zio_priority,	\
+	__entry->zio_type, __entry->zio_priority,			\
 	__entry->zio_size, __entry->zio_orig_size, __entry->zio_offset,	\
 	__entry->zio_timestamp, __entry->zio_delta, __entry->zio_delay,	\
 	__entry->zio_flags, __entry->zio_stage, __entry->zio_pipeline,	\
diff --git a/include/sys/zio.h b/include/sys/zio.h
index 5dcd7fe073a0..545b9cf0c3c5 100644
--- a/include/sys/zio.h
+++ b/include/sys/zio.h
@@ -451,7 +451,6 @@ struct zio {
 	zio_type_t	io_type;
 	enum zio_child	io_child_type;
 	enum trim_flag	io_trim_flags;
-	int		io_cmd;
 	zio_priority_t	io_priority;
 	uint8_t		io_reexecute;
 	uint8_t		io_state[ZIO_WAIT_TYPES];
diff --git a/module/os/freebsd/zfs/vdev_file.c b/module/os/freebsd/zfs/vdev_file.c
index a65dfec86caf..888c8e7f8863 100644
--- a/module/os/freebsd/zfs/vdev_file.c
+++ b/module/os/freebsd/zfs/vdev_file.c
@@ -255,14 +255,7 @@ vdev_file_io_start(zio_t *zio)
 			return;
 		}
 
-		switch (zio->io_cmd) {
-		case DKIOCFLUSHWRITECACHE:
-			zio->io_error = zfs_file_fsync(vf->vf_file,
-			    O_SYNC|O_DSYNC);
-			break;
-		default:
-			zio->io_error = SET_ERROR(ENOTSUP);
-		}
+		zio->io_error = zfs_file_fsync(vf->vf_file, O_SYNC|O_DSYNC);
 
 		zio_execute(zio);
 		return;
diff --git a/module/os/freebsd/zfs/vdev_geom.c b/module/os/freebsd/zfs/vdev_geom.c
index 196d67b4b595..264dfa5c9237 100644
--- a/module/os/freebsd/zfs/vdev_geom.c
+++ b/module/os/freebsd/zfs/vdev_geom.c
@@ -1153,42 +1153,31 @@ vdev_geom_io_start(zio_t *zio)
 
 	vd = zio->io_vd;
 
-	switch (zio->io_type) {
-	case ZIO_TYPE_IOCTL:
+	if (zio->io_type == ZIO_TYPE_IOCTL) {
 		/* XXPOLICY */
 		if (!vdev_readable(vd)) {
 			zio->io_error = SET_ERROR(ENXIO);
 			zio_interrupt(zio);
 			return;
-		} else {
-			switch (zio->io_cmd) {
-			case DKIOCFLUSHWRITECACHE:
-				if (zfs_nocacheflush ||
-				    vdev_geom_bio_flush_disable)
-					break;
-				if (vd->vdev_nowritecache) {
-					zio->io_error = SET_ERROR(ENOTSUP);
-					break;
-				}
-				goto sendreq;
-			default:
-				zio->io_error = SET_ERROR(ENOTSUP);
-			}
 		}
 
-		zio_execute(zio);
-		return;
-	case ZIO_TYPE_TRIM:
-		if (!vdev_geom_bio_delete_disable) {
-			goto sendreq;
+		if (zfs_nocacheflush || vdev_geom_bio_flush_disable) {
+			zio_execute(zio);
+			return;
+		}
+
+		if (vd->vdev_nowritecache) {
+			zio->io_error = SET_ERROR(ENOTSUP);
+			zio_execute(zio);
+			return;
+		}
+	} else if (zio->io_type == ZIO_TYPE_TRIM) {
+		if (vdev_geom_bio_delete_disable) {
+			zio_execute(zio);
+			return;
 		}
-		zio_execute(zio);
-		return;
-	default:
-			;
-		/* PASSTHROUGH --- placate compiler */
 	}
-sendreq:
+
 	ASSERT(zio->io_type == ZIO_TYPE_READ ||
 	    zio->io_type == ZIO_TYPE_WRITE ||
 	    zio->io_type == ZIO_TYPE_TRIM ||
diff --git a/module/os/linux/zfs/vdev_disk.c b/module/os/linux/zfs/vdev_disk.c
index f3f0c0875210..554ed22b9df8 100644
--- a/module/os/linux/zfs/vdev_disk.c
+++ b/module/os/linux/zfs/vdev_disk.c
@@ -1403,38 +1403,29 @@ vdev_disk_io_start(zio_t *zio)
 	case ZIO_TYPE_IOCTL:
 
 		if (!vdev_readable(v)) {
-			rw_exit(&vd->vd_lock);
-			zio->io_error = SET_ERROR(ENXIO);
-			zio_interrupt(zio);
-			return;
-		}
-
-		switch (zio->io_cmd) {
-		case DKIOCFLUSHWRITECACHE:
-
-			if (zfs_nocacheflush)
-				break;
-
-			if (v->vdev_nowritecache) {
-				zio->io_error = SET_ERROR(ENOTSUP);
-				break;
-			}
-
+			/* Drive not there, can't flush */
+			error = SET_ERROR(ENXIO);
+		} else if (zfs_nocacheflush) {
+			/* Flushing disabled by operator, declare success */
+			error = 0;
+		} else if (v->vdev_nowritecache) {
+			/* This vdev not capable of flushing */
+			error = SET_ERROR(ENOTSUP);
+		} else {
+			/*
+			 * Issue the flush. If successful, the response will
+			 * be handled in the completion callback, so we're done.
+			 */
 			error = vdev_disk_io_flush(BDH_BDEV(vd->vd_bdh), zio);
 			if (error == 0) {
 				rw_exit(&vd->vd_lock);
 				return;
 			}
-
-			zio->io_error = error;
-
-			break;
-
-		default:
-			zio->io_error = SET_ERROR(ENOTSUP);
 		}
 
+		/* Couldn't issue the flush, so set the error and return it */
 		rw_exit(&vd->vd_lock);
+		zio->io_error = error;
 		zio_execute(zio);
 		return;
 
diff --git a/module/os/linux/zfs/vdev_file.c b/module/os/linux/zfs/vdev_file.c
index 5abc0426d1a7..2b483c9a9fa4 100644
--- a/module/os/linux/zfs/vdev_file.c
+++ b/module/os/linux/zfs/vdev_file.c
@@ -250,33 +250,27 @@ vdev_file_io_start(zio_t *zio)
 			return;
 		}
 
-		switch (zio->io_cmd) {
-		case DKIOCFLUSHWRITECACHE:
-
-			if (zfs_nocacheflush)
-				break;
-
-			/*
-			 * We cannot safely call vfs_fsync() when PF_FSTRANS
-			 * is set in the current context.  Filesystems like
-			 * XFS include sanity checks to verify it is not
-			 * already set, see xfs_vm_writepage().  Therefore
-			 * the sync must be dispatched to a different context.
-			 */
-			if (__spl_pf_fstrans_check()) {
-				VERIFY3U(taskq_dispatch(vdev_file_taskq,
-				    vdev_file_io_fsync, zio, TQ_SLEEP), !=,
-				    TASKQID_INVALID);
-				return;
-			}
-
-			zio->io_error = zfs_file_fsync(vf->vf_file,
-			    O_SYNC | O_DSYNC);
-			break;
-		default:
-			zio->io_error = SET_ERROR(ENOTSUP);
+		if (zfs_nocacheflush) {
+			zio_execute(zio);
+			return;
 		}
 
+		/*
+		 * We cannot safely call vfs_fsync() when PF_FSTRANS
+		 * is set in the current context.  Filesystems like
+		 * XFS include sanity checks to verify it is not
+		 * already set, see xfs_vm_writepage().  Therefore
+		 * the sync must be dispatched to a different context.
+		 */
+		if (__spl_pf_fstrans_check()) {
+			VERIFY3U(taskq_dispatch(vdev_file_taskq,
+			    vdev_file_io_fsync, zio, TQ_SLEEP), !=,
+			    TASKQID_INVALID);
+			return;
+		}
+
+		zio->io_error = zfs_file_fsync(vf->vf_file, O_SYNC | O_DSYNC);
+
 		zio_execute(zio);
 		return;
 	} else if (zio->io_type == ZIO_TYPE_TRIM) {
diff --git a/module/zfs/vdev_draid.c b/module/zfs/vdev_draid.c
index ec961255fd64..7769ed6a377a 100644
--- a/module/zfs/vdev_draid.c
+++ b/module/zfs/vdev_draid.c
@@ -2557,15 +2557,11 @@ vdev_draid_spare_ioctl(zio_t *zio)
 	vdev_t *vd = zio->io_vd;
 	int error = 0;
 
-	if (zio->io_cmd == DKIOCFLUSHWRITECACHE) {
-		for (int c = 0; c < vd->vdev_children; c++) {
-			zio_nowait(zio_vdev_child_io(zio, NULL,
-			    vd->vdev_child[c], zio->io_offset, zio->io_abd,
-			    zio->io_size, zio->io_type, zio->io_priority, 0,
-			    vdev_draid_spare_child_done, zio));
-		}
-	} else {
-		error = SET_ERROR(ENOTSUP);
+	for (int c = 0; c < vd->vdev_children; c++) {
+		zio_nowait(zio_vdev_child_io(zio, NULL,
+		    vd->vdev_child[c], zio->io_offset, zio->io_abd,
+		    zio->io_size, zio->io_type, zio->io_priority, 0,
+		    vdev_draid_spare_child_done, zio));
 	}
 
 	return (error);
diff --git a/module/zfs/zfs_fm.c b/module/zfs/zfs_fm.c
index 481af2ba826b..2f43c4aa41b8 100644
--- a/module/zfs/zfs_fm.c
+++ b/module/zfs/zfs_fm.c
@@ -1096,10 +1096,7 @@ zfs_ereport_is_valid(const char *subclass, spa_t *spa, vdev_t *vd, zio_t *zio)
 		return (B_FALSE);
 
 	if (zio != NULL) {
-		/*
-		 * If this is not a read or write zio, ignore the error.  This
-		 * can occur if the DKIOCFLUSHWRITECACHE ioctl fails.
-		 */
+		/* If this is not a read or write zio, ignore the error */
 		if (zio->io_type != ZIO_TYPE_READ &&
 		    zio->io_type != ZIO_TYPE_WRITE)
 			return (B_FALSE);
diff --git a/module/zfs/zil.c b/module/zfs/zil.c
index 1af357c58006..34be54b337fd 100644
--- a/module/zfs/zil.c
+++ b/module/zfs/zil.c
@@ -125,10 +125,9 @@ static kstat_t *zil_kstats_global;
 int zil_replay_disable = 0;
 
 /*
- * Disable the DKIOCFLUSHWRITECACHE commands that are normally sent to
- * the disk(s) by the ZIL after an LWB write has completed. Setting this
- * will cause ZIL corruption on power loss if a volatile out-of-order
- * write cache is enabled.
+ * Disable the flush commands that are normally sent to the disk(s) by the ZIL
+ * after an LWB write has completed. Setting this will cause ZIL corruption on
+ * power loss if a volatile out-of-order write cache is enabled.
  */
 static int zil_nocacheflush = 0;
 
@@ -1406,19 +1405,17 @@ zil_lwb_add_txg(lwb_t *lwb, uint64_t txg)
 }
 
 /*
- * This function is a called after all vdevs associated with a given lwb
- * write have completed their DKIOCFLUSHWRITECACHE command; or as soon
- * as the lwb write completes, if "zil_nocacheflush" is set. Further,
- * all "previous" lwb's will have completed before this function is
- * called; i.e. this function is called for all previous lwbs before
- * it's called for "this" lwb (enforced via zio the dependencies
- * configured in zil_lwb_set_zio_dependency()).
+ * This function is a called after all vdevs associated with a given lwb write
+ * have completed their flush command; or as soon as the lwb write completes,
+ * if "zil_nocacheflush" is set. Further, all "previous" lwb's will have
+ * completed before this function is called; i.e. this function is called for
+ * all previous lwbs before it's called for "this" lwb (enforced via zio the
+ * dependencies configured in zil_lwb_set_zio_dependency()).
  *
- * The intention is for this function to be called as soon as the
- * contents of an lwb are considered "stable" on disk, and will survive
- * any sudden loss of power. At this point, any threads waiting for the
- * lwb to reach this state are signalled, and the "waiter" structures
- * are marked "done".
+ * The intention is for this function to be called as soon as the contents of
+ * an lwb are considered "stable" on disk, and will survive any sudden loss of
+ * power. At this point, any threads waiting for the lwb to reach this state
+ * are signalled, and the "waiter" structures are marked "done".
  */
 static void
 zil_lwb_flush_vdevs_done(zio_t *zio)
@@ -1532,17 +1529,16 @@ zil_lwb_flush_wait_all(zilog_t *zilog, uint64_t txg)
 }
 
 /*
- * This is called when an lwb's write zio completes. The callback's
- * purpose is to issue the DKIOCFLUSHWRITECACHE commands for the vdevs
- * in the lwb's lwb_vdev_tree. The tree will contain the vdevs involved
- * in writing out this specific lwb's data, and in the case that cache
- * flushes have been deferred, vdevs involved in writing the data for
- * previous lwbs. The writes corresponding to all the vdevs in the
- * lwb_vdev_tree will have completed by the time this is called, due to
- * the zio dependencies configured in zil_lwb_set_zio_dependency(),
- * which takes deferred flushes into account. The lwb will be "done"
- * once zil_lwb_flush_vdevs_done() is called, which occurs in the zio
- * completion callback for the lwb's root zio.
+ * This is called when an lwb's write zio completes. The callback's purpose is
+ * to issue the flush commands for the vdevs in the lwb's lwb_vdev_tree. The
+ * tree will contain the vdevs involved in writing out this specific lwb's
+ * data, and in the case that cache flushes have been deferred, vdevs involved
+ * in writing the data for previous lwbs. The writes corresponding to all the
+ * vdevs in the lwb_vdev_tree will have completed by the time this is called,
+ * due to the zio dependencies configured in zil_lwb_set_zio_dependency(),
+ * which takes deferred flushes into account. The lwb will be "done" once
+ * zil_lwb_flush_vdevs_done() is called, which occurs in the zio completion
+ * callback for the lwb's root zio.
  */
 static void
 zil_lwb_write_done(zio_t *zio)
@@ -1601,19 +1597,18 @@ zil_lwb_write_done(zio_t *zio)
 	}
 
 	/*
-	 * If this lwb does not have any threads waiting for it to
-	 * complete, we want to defer issuing the DKIOCFLUSHWRITECACHE
-	 * command to the vdevs written to by "this" lwb, and instead
-	 * rely on the "next" lwb to handle the DKIOCFLUSHWRITECACHE
-	 * command for those vdevs. Thus, we merge the vdev tree of
-	 * "this" lwb with the vdev tree of the "next" lwb in the list,
-	 * and assume the "next" lwb will handle flushing the vdevs (or
-	 * deferring the flush(s) again).
+	 * If this lwb does not have any threads waiting for it to complete, we
+	 * want to defer issuing the flush command to the vdevs written to by
+	 * "this" lwb, and instead rely on the "next" lwb to handle the flush
+	 * command for those vdevs. Thus, we merge the vdev tree of "this" lwb
+	 * with the vdev tree of the "next" lwb in the list, and assume the
+	 * "next" lwb will handle flushing the vdevs (or deferring the flush(s)
+	 * again).
 	 *
-	 * This is a useful performance optimization, especially for
-	 * workloads with lots of async write activity and few sync
-	 * write and/or fsync activity, as it has the potential to
-	 * coalesce multiple flush commands to a vdev into one.
+	 * This is a useful performance optimization, especially for workloads
+	 * with lots of async write activity and few sync write and/or fsync
+	 * activity, as it has the potential to coalesce multiple flush
+	 * commands to a vdev into one.
 	 */
 	if (list_is_empty(&lwb->lwb_waiters) && nlwb != NULL) {
 		zil_lwb_flush_defer(lwb, nlwb);
@@ -1663,16 +1658,16 @@ zil_lwb_set_zio_dependency(zilog_t *zilog, lwb_t *lwb)
 	 * If the previous lwb's write hasn't already completed, we also want
 	 * to order the completion of the lwb write zios (above, we only order
 	 * the completion of the lwb root zios). This is required because of
-	 * how we can defer the DKIOCFLUSHWRITECACHE commands for each lwb.
+	 * how we can defer the flush commands for each lwb.
 	 *
-	 * When the DKIOCFLUSHWRITECACHE commands are deferred, the previous
-	 * lwb will rely on this lwb to flush the vdevs written to by that
-	 * previous lwb. Thus, we need to ensure this lwb doesn't issue the
-	 * flush until after the previous lwb's write completes. We ensure
-	 * this ordering by setting the zio parent/child relationship here.
+	 * When the flush commands are deferred, the previous lwb will rely on
+	 * this lwb to flush the vdevs written to by that previous lwb. Thus,
+	 * we need to ensure this lwb doesn't issue the flush until after the
+	 * previous lwb's write completes. We ensure this ordering by setting
+	 * the zio parent/child relationship here.
 	 *
-	 * Without this relationship on the lwb's write zio, it's possible
-	 * for this lwb's write to complete prior to the previous lwb's write
+	 * Without this relationship on the lwb's write zio, it's possible for
+	 * this lwb's write to complete prior to the previous lwb's write
 	 * completing; and thus, the vdevs for the previous lwb would be
 	 * flushed prior to that lwb's data being written to those vdevs (the
 	 * vdevs are flushed in the lwb write zio's completion handler,
@@ -3499,8 +3494,8 @@ zil_commit_itx_assign(zilog_t *zilog, zil_commit_waiter_t *zcw)
  *      callback of the lwb's zio[*].
  *
  *      * Actually, the waiters are signaled in the zio completion
- *        callback of the root zio for the DKIOCFLUSHWRITECACHE commands
- *        that are sent to the vdevs upon completion of the lwb zio.
+ *        callback of the root zio for the flush commands that are sent to
+ *        the vdevs upon completion of the lwb zio.
  *
  *   2. When the itxs are inserted into the ZIL's queue of uncommitted
  *      itxs, the order in which they are inserted is preserved[*]; as
diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index 4aa08f3b30f5..031fc3d5135d 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -1631,11 +1631,9 @@ zio_flush(zio_t *pio, vdev_t *vd)
 		return;
 
 	if (vd->vdev_children == 0) {
-		zio_t *zio = zio_create(pio, vd->vdev_spa, 0, NULL, NULL, 0, 0,
+		zio_nowait(zio_create(pio, vd->vdev_spa, 0, NULL, NULL, 0, 0,
 		    NULL, NULL, ZIO_TYPE_IOCTL, ZIO_PRIORITY_NOW, flags, vd, 0,
-		    NULL, ZIO_STAGE_OPEN, ZIO_IOCTL_PIPELINE);
-		zio->io_cmd = DKIOCFLUSHWRITECACHE;
-		zio_nowait(zio);
+		    NULL, ZIO_STAGE_OPEN, ZIO_IOCTL_PIPELINE));
 	} else {
 		for (uint64_t c = 0; c < vd->vdev_children; c++)
 			zio_flush(pio, vd->vdev_child[c]);
@@ -4241,8 +4239,7 @@ zio_vdev_io_assess(zio_t *zio)
 	 * boolean flag so that we don't bother with it in the future.
 	 */
 	if ((zio->io_error == ENOTSUP || zio->io_error == ENOTTY) &&
-	    zio->io_type == ZIO_TYPE_IOCTL &&
-	    zio->io_cmd == DKIOCFLUSHWRITECACHE && vd != NULL)
+	    zio->io_type == ZIO_TYPE_IOCTL && vd != NULL)
 		vd->vdev_nowritecache = B_TRUE;
 
 	if (zio->io_error)