PR 59570 - tar fails with physical tape drives - root cause likely found ?

[vom513 <vom513%gmail.com@localhost>]

Hello all,

I had posted about this a while ago.  In short - writing to a real SCSI tape drive on recent/release NetBSD works.  Reading the archive back always results in tar header errors (regardless of blocksize etc).

I had found through brute force installs and playing high/low with versions that the newest NetBSD that didn’t have this issue was 7.2

It seems that between 7.2 and 8.0 there was some refactor work in scsipi to make things MPSAFE.  From my very-much-not-a-C-dev-or-kernel-dev perspective I’m thinking this might have been what caused this.

I took st.c and removed the MPSAFE flags on a 10.1 kernel and no longer have this issue.  I have updated the bug as well with more details:

https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=59570

If anyone has the cycles and know-how to take a better look at this and what the “real” root cause (not my fireaxe of just disabling it…) that would be awesome.  I am more than happy to test kernels and code on my system.