Andrew Gallant 93943793c3 worker: better error handling for memory maps ...

Previously, we would bail out of using memory maps if we could detect
ahead of time that opening a memory map would fail. The only case we
checked was whether the file size was 0 or not.

This is actually insufficient. The mmap call can return ENODEV errors
when a file doesn't support memory maps. This is the case for new files
exposed by Linux, for example,
/sys/devices/system/cpu/vulnerabilities/meltdown.

We fix this by checking the actual error codes returned by the mmap call.
If ENODEV (or EOVERFLOW) is returned, then we fall back to regular `read`
calls. If any other error occurs, we report it to the user.

Fixes #760

2018-01-31 19:20:36 -05:00

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