5bbcfbaa11
TL;DR This effectively reverts8327fd1b11,eaba9bb3e6, and its follow-ups, as the original issue was already fixed by the kernel side. The original issue that the above commits tried to 'fix' is that reading phys_port_name triggers a lock in the kernel, hence processing multiple interfaces at the same time causes extreme slow down. To workaround the issue, the above commits made several necessary information retrieved through netlink instead of sysfs attributes. A patch set for the kernel was proposed as a fix for the issue: https://lore.kernel.org/all/20210928125500.167943-1-atenart@kernel.org/ and some of them were merged to v5.16:146e5e7333, It has been already backported to 5.4.160, 5.10.80, 5.14.19, and 5.15.3. When these commits were proposed, it is already claimed that such issue should be fixed by the kernel side, and udevd should not workaround it. Neverthless the feature was introduced, as these have theoretical performance improvement, even if phys_port_name sysattr does not have the above issue, as in that way udevd can obtain multiple information about the interface with a single netlink socket operation. See the discussion in #20744. However, in reality, only `iflink`, `type`, `address`, and `phys_port_name` attributes from netlink are used in the udev net_id builtin command. Hence, after the original issue being fixed in the kernel side, there should be almost no performance improvement for udevd. Furthermore, combining attributes from netlink and sysfs makes hard to test net_id builtin. See #21725. Let's drop mostly meaningless code, and make net_id builtin easily testable. Closes #21725.
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