/etc/modprobe.d/blacklist-ath_pci.conf is in kmod 22-1ubuntu5.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | # For some Atheros 5K RF MACs, the madwifi driver loads buts fails to
# correctly initialize the hardware, leaving it in a state from
# which ath5k cannot recover. To prevent this condition, stop
# madwifi from loading by default. Use Jockey to select one driver
# or the other. (Ubuntu: #315056, #323830)
blacklist ath_pci
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