Wrong permissions + Timing issue in NewOutput/NewInput

[andreacioni]

Hi @brian-armstrong,

I'm start testing your work on Beaglebone Black, I'm getting the following error: failed to open gpio 60 direction file for writing. I've changed last parameter in all occurences of os.OpenFile in sys.fs to 0666 (r/w for everyone) and everything works. I'm using it as a non-root user but my account belongs to gpio group.

Andrea Cioni

[andreacioni]

Hi Brian,

there is not only a problem with permissions. As I said here #8 , I'm having timing issue (causing the same error above: "failed to open gpio X direction file for writing") related to fast Sleep in NewOutput. Increasing it to 1 second solved it and should be safe and quite short.
What do you think?

Cheers

[brian-armstrong]

1 second feels like a while to need to sleep in a library like this. I think it's sort of exposing the limitations of this approach. Ideally we could get notified by the kernel that the file has been exported, but I don't know of a good way of doing that without bringing in inotify, which might be fairly heavyweight for this.

I think the next best solution would be to poll this file fairly aggressively, maybe every 5ms or so. I would feel more comfortable watching it for up to a second if we could spend less time watching it, on average.

Also, are you sure the file mode is causing an issue? It seems weird that the file would export as a different user than the user exporting it. At any rate, I think 0660 would be more appropriate here than 0666.