virtio: use modern mode for transitional device by default
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Authored by timo.voelker_fh-muenster.de on Mar 17 2026, 10:07 AM.

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bryanv
grehan
tuexen
imp

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rG0b39d72d0491: virtio: use modern mode for transitional device by default

Summary

This patch changes the default value of the loader tunable hw.virtio.pci.transitional to 1. This means, virtio uses the modern mode for transitional devices by default.

Also, this patch corrects the description of the loader tunable in the man page.

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rG FreeBSD src repository

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Event Timeline

timo.voelker_fh-muenster.de created this revision.Mar 17 2026, 10:07 AM

Herald added a subscriber: ziaee. · View Herald TranscriptMar 17 2026, 10:07 AM

timo.voelker_fh-muenster.de requested review of this revision.Mar 17 2026, 10:07 AM

Why changing hw.virtio.pci.transitional to 1 by default:

VirtualBox provides a transitional VirtIO network device, which seems not to work in legacy mode. By using modern mode by default, FreeBSD does not run in this VirtualBox bug (by default).
The return values of vtpci_modern_probe and vtpci_legacy_probe were chosen to prefer modern mode but hw.virtio.pci.transitional=0 prevents modern mode. Setting hw.virtio.pci.transitional to 1 by default seems a better fit.

tuexen accepted this revision.Apr 4 2026, 2:52 PM

This revision is now accepted and ready to land.Apr 4 2026, 2:52 PM

Closed by commit rG0b39d72d0491: virtio: use modern mode for transitional device by default (authored by timo.voelker_fh-muenster.de, committed by tuexen). · Explain WhyApr 4 2026, 2:54 PM

This revision was automatically updated to reflect the committed changes.

tuexen added a commit: rG0b39d72d0491: virtio: use modern mode for transitional device by default.

timo.voelker_fh-muenster.de mentioned this in D57392: virtio: remove byte conversion function calls in modern pci.Jun 2 2026, 11:39 AM