Mac: sporadic vnode I/O errors

There seem to be a number of places in the kext’s vnode/fileop handler where I/O (reading attributes, etc.) occasionally fails. In a few places there are asserts that even take down the system in case of such failures. We need to track down all the failure cases, some common root causes, and handle them correctly and gracefully in the kext instead of crashing the system.

Known failure cases:

• Failed assertions on reading file attributes
• Panics in file close events

Reports of more cases appreciated.

[pmj]

Following out-of-band discussion, I’m going to wrap up most of the error logging I added with #555 into a PR we can merge into master, so that we can get a better overall picture of these errors and so that they are logged automatically on end user machines (c.f. #396) as they may help with diagnosing problems.

Additionally, we want to start mitigating the known problems, particularly the name cache misses. (with a view to implementing something along the lines of #338)

[pmj]

Yeah, this has turned up before - it seems that by the time we get the KAUTH_FILEOP_CLOSE event (presumably on a file that was deleted before the last process closed its handle), the vnode can already be in the process of being recycled. I believe this behaviour is part of what needs to be solved in #209 so I’ll leave the error log in there until that issue has been resolved - also in case we run into a different type of error in the same location. Still - thanks for reporting!