[Bug 292322] Hastd failing to g_attach device on FreeBSD 15.0

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=292322

--- Comment #7 from Glen Barber <gjb@FreeBSD.org> ---
I independently reproduced this exact issue while testing HAST for a project
(two FreeBSD 15.1-RELEASE VMs).

Same symptom: primary stuck at degraded, secondary logging Unable to receive
header from tcp://...: Operation timed out., and the same g_dev_taste ...
failed to g_attach, error=6 kernel message.

Diagnostic detail that may help confirm the root cause: a packet capture during
a role primary attempt shows a completely clean TCP three-way handshake
followed by ~20 seconds of total silence in both directions before the
connection times out — confirming the network layer is healthy and the primary
genuinely never transmits anything. 'procstat -t' on the primary's worker
process shows kernel threads parked in sbwait with no forward progress, and
'truss -H' confirms zero connect/send/recv syscalls occur — consistent with
Martin's diagnosis of the worker blocking on recv(2)/MSG_WAITALL in the
connection-migration path.

I also confirmed this is not 15-specific: pairing a FreeBSD 16.0-CURRENT node
(main-n288684-420428718da7) with a 15.1-RELEASE node reproduces the identical
failure, so the affected code path is still present in HEAD as of 2026-08-29.

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