On Tue, Nov 6, 2012 at 4:55 PM, Nicholas A. Bellinger
<nab@xxxxxxxxxxxxxxx> wrote:
> > - (cmd->stat_sn < exp_statsn)) {
> Is there an actual bug this patch fixes, or some initiator that expects
> ExpStatSN to be using SNA..? (CC'ing mnc + hare)
Well, consider what happens with the original code as above. stat_sn
is a u32, so on a connection that lasts a long time (though 4 billion
commands doesn't last that long at high IOPS), we'll eventually hit a
case where our stat_sn will wrap around from UINT_MAX to 0. And when
that happens, if the initiator sends us an exp_stat_sn of UINT_MAX-1
or something, then the test above will spuriously succeed.
The iscsi spec talks about using mod(2**32) arithmetic for StatSN. I
think what that means is that you have to take wraparound into
account. Strictly speaking that doesn't necessarily mean SNA I guess,
but that seems to be the easiest way to deal with it.
- R.
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