From ca18c876e52dca44bed961ab93cef47538ae9022 Mon Sep 17 00:00:00 2001
From: Rob Norris <rob.norris@klarasystems.com>
Date: Tue, 29 Aug 2023 22:02:45 +1000
Subject: [PATCH] zio: function to issue flushes by trace tree

If you have a trace tree from, say, a write, hand it directly to
zio_flush_traced() to flush only the leaf vdevs that were involved in
the write.

Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
---
 include/sys/zio.h |  1 +
 module/zfs/zio.c  | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/sys/zio.h b/include/sys/zio.h
index daa2b2d23f..9adeb5f1e8 100644
--- a/include/sys/zio.h
+++ b/include/sys/zio.h
@@ -594,6 +594,7 @@ extern zio_t *zio_free_sync(zio_t *pio, spa_t *spa, uint64_t txg,
 extern int zio_alloc_zil(spa_t *spa, objset_t *os, uint64_t txg,
     blkptr_t *new_bp, uint64_t size, boolean_t *slog);
 extern void zio_flush(zio_t *zio, vdev_t *vd, boolean_t propagate);
+extern void zio_flush_traced(zio_t *zio, avl_tree_t *t, boolean_t propagate);
 extern void zio_shrink(zio_t *zio, uint64_t size);
 
 extern int zio_wait(zio_t *zio);
diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index 6597b0ff29..bee0324578 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -1613,6 +1613,36 @@ zio_flush(zio_t *pio, vdev_t *vd, boolean_t propagate)
 	zio_nowait(zio);
 }
 
+void
+zio_flush_traced(zio_t *pio, avl_tree_t *t, boolean_t propagate)
+{
+	const int cmd = DKIOCFLUSHWRITECACHE;
+	const zio_flag_t flags =
+	    ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_RETRY |
+	    (propagate ? 0 : ZIO_FLAG_DONT_PROPAGATE);
+	spa_t *spa = pio->io_spa;
+	zio_t *fio, *zio;
+	zio_vdev_trace_t *zvt;
+	vdev_t *vd;
+
+	fio = zio_null(pio, spa, NULL, NULL, NULL, flags);
+
+	for (zvt = avl_first(t); zvt != NULL; zvt = AVL_NEXT(t, zvt)) {
+		vd = vdev_lookup_by_guid(spa->spa_root_vdev, zvt->zvt_guid);
+		if (vd == NULL)
+			continue;
+		if (vd->vdev_children == 0) {
+			zio = zio_create(fio, 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 = cmd;
+			zio_nowait(zio);
+		}
+	}
+
+	zio_nowait(fio);
+}
+
 void
 zio_shrink(zio_t *zio, uint64_t size)
 {