On Sat, May 13, 2017 at 1:26 AM, Luke Dashjr <luke@dashjr.org> wrote:

> Versionbits change/lose their meaning after the deployment timeout. For
> this
> reason, the timeout must be specified so the check is skipped when that
> occurs.
>

To add a timeout a user can optionally bundle a pair of similar
transactions.  One with the transaction version bits set and a second with
a locktime set.  The effect is the same.

Also, doing it the way you describe would fail to enforce that BIP9 is
> actually in use for the block version; you could simply add that as an
> additional condition, but it seems pretty hacky since you wouldn't be able
> to
> upgrade versionbits anymore...
>


My formal condition does include a check for the block version (I've
corrected the constants below):

(txVersion & 0xe0000000 != 0x200000000) || (*(blkVersion & 0xe0000000 =
0x200000000)* && (blkVersion & txVersion = txVersion))

Nothing here prevents upgrading versionbits AFAICT.  Any txVersion that
does not begin with 0b001 is unconditionally acceptable and available for
further soft-forking.