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iflib: initialize netmap with the correct number of descriptors

Authored by vmaffione on Jul 1 2020, 7:24 PM.



In case the network device has a RX or TX control queue, the correct number of TX/RX descriptors is contained
in the second entry of the isc_ntxd (or isc_nrxd) array, rather than in the first entry.
This case is correctly handled by iflib_device_register() and iflib_pseudo_register(), but not by
iflib_netmap_attach(). If the first entry is larger than the second, this can result in a panic.
This change fixes the bug by introducing two helper functions that also lead to some code simplification.

PR 247647

Test Plan

Tested on vmx0 interface on QEMU/KVM. After the fix, iflib does not panic anymore.

Diff Detail

rS FreeBSD src repository
Automatic diff as part of commit; lint not applicable.
Automatic diff as part of commit; unit tests not applicable.

Event Timeline

The PR reporter has tested the patch and confirmed that the panic has been fixed. See

This revision was not accepted when it landed; it landed in state Needs Review.Jul 20 2020, 9:09 PM
This revision was automatically updated to reflect the committed changes.