Function vdev_config_sync

freebsd/contrib/openzfs/module/zfs/vdev_label.c:1861–1984

* Sync the uberblock and any changes to the vdev configuration. * * The order of operations is carefully crafted to ensure that * if the system panics or loses power at any time, the state on disk * is still transactionally consistent. The in-line comments below * describe the failure semantics at each stage. * * Moreover, vdev_config_sync() is designed to be idempotent: if it fails * at

 * at any time, you can just call it again, and it will resume its work.
 */
int
vdev_config_sync(vdev_t **svd, int svdcount, uint64_t txg)
{
	spa_t *spa = svd[0]->vdev_spa;
	uberblock_t *ub = &spa->spa_uberblock;
	int error = 0;
	int flags = ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_CANFAIL;

	ASSERT(svdcount != 0);
retry:
	/*
	 * Normally, we don't want to try too hard to write every label and
	 * uberblock.  If there is a flaky disk, we don't want the rest of the
	 * sync process to block while we retry.  But if we can't write a
	 * single label out, we should retry with ZIO_FLAG_TRYHARD before
	 * bailing out and declaring the pool faulted.
	 */
	if (error != 0) {
		if ((flags & ZIO_FLAG_TRYHARD) != 0)
			return (error);
		flags |= ZIO_FLAG_TRYHARD;
	}

	ASSERT(ub->ub_txg <= txg);

	/*
	 * If this isn't a resync due to I/O errors,
	 * and nothing changed in this transaction group,
	 * and the vdev configuration hasn't changed,
	 * then there's nothing to do.
	 */
	if (ub->ub_txg < txg) {
		boolean_t changed = uberblock_update(ub, spa->spa_root_vdev,
		    txg, spa->spa_mmp.mmp_delay);

		if (!changed && list_is_empty(&spa->spa_config_dirty_list))
			return (0);
	}

	if (txg > spa_freeze_txg(spa))
		return (0);

	ASSERT(txg <= spa->spa_final_txg);

	/*
	 * Flush the write cache of every disk that's been written to
	 * in this transaction group.  This ensures that all blocks
	 * written in this txg will be committed to stable storage
	 * before any uberblock that references them.
	 */
	zio_t *zio = zio_root(spa, NULL, NULL, flags);

	for (vdev_t *vd =
	    txg_list_head(&spa->spa_vdev_txg_list, TXG_CLEAN(txg)); vd != NULL;
	    vd = txg_list_next(&spa->spa_vdev_txg_list, vd, TXG_CLEAN(txg)))
		zio_flush(zio, vd);

	(void) zio_wait(zio);