zfs_netbsd_gop_markupdate: actually update file timestamp

the implementation before this commit was basically no-op.

some notes:

* this is (ab)used in zfs_netbsd_write for fifo/spec vnodes.
  i feel it's a bit excessive to update the timestamp on every
  writes to /dev/null. unfortunately, zfs doesn't have nodevmtime
  option. well, i suspect netbsd is the only os with the traditional
  devmtime behavior these days. we may want to implement delayed
  mtime update as ffs does.

* this is used by zfs_netbsd_putpages via genfs_putpages. but it's
  redundant because zfs_putapage updates the timestamp as well.

* this is not used by zfs_netbsd_getpages. zfs doesn't use
  genfs_getpages. zfs_netbsd_getpages doesn't have the
  corresponding logic either. maybe it's ok for most of applications
  as far as mtime will be updated sooner or later.

Author: yamt

external/cddl/osnet/dist/uts/common/fs/zfs/zfs_vnops.c

@@ -6237,6 +6237,8 @@ zfs_netbsd_gop_markupdate(vnode_t *vp, int flags)
 	KASSERT(flags == GOP_UPDATE_MODIFIED);
 
 	tx = dmu_tx_create(zfsvfs->z_os);
+	dmu_tx_hold_sa(tx, zp->z_sa_hdl, B_FALSE);
+	zfs_sa_upgrade_txholds(tx, zp);
 	err = dmu_tx_assign(tx, TXG_WAIT);
 	if (err != 0) {
 		dmu_tx_abort(tx);
@@ -6245,7 +6247,11 @@ zfs_netbsd_gop_markupdate(vnode_t *vp, int flags)
 	SA_ADD_BULK_ATTR(bulk, count, SA_ZPL_MTIME(zfsvfs), NULL, &mtime, 16);
 	SA_ADD_BULK_ATTR(bulk, count, SA_ZPL_CTIME(zfsvfs), NULL, &ctime, 16);
 	zfs_tstamp_update_setup(zp, CONTENT_MODIFIED, mtime, ctime, B_TRUE);
+	err = sa_bulk_update(zp->z_sa_hdl, bulk, count, tx);
 	dmu_tx_commit(tx);
+	if (err != 0) {
+		printf("%s: sa_bulk_update failed with %d\n", __func__, err);
+	}
 }
 
 static int