Add support for naming FreeBSD tun devices #903
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overlay/tun_freebsd.go
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| @@ -95,15 +93,18 @@ func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, defaultMTU int | |||
| return nil, err | |||
| } | |||
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| fileFd := file.Fd() | |||
| err = syscall.SetNonblock(int(fileFd), true) | |||
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This call is necessary due to a side-effect of file.Fd(). By default, the FIle returned by OpenFile is in non-blocking mode. If we leave it in blocking mode, Nebula will hang when we try to destroy the interface in the Close method (part of cleanly shutting down Nebula.)
Based on discussion with Go maintainers, it seems that file.Fd() should only be called if you're done using the File object. In this case we are not, so it's better to use file.SyscallConn() which I've updated this PR to do.
We do also call syscall.SetNonblock in tun_darwin.go. I suspect this is because the fd returned by unix.Socket() is not non-blocking by default, and we want to place it in non-blocking mode before calling NewFile:
NewFile returns a new File with the given file descriptor and name. The returned value will be nil if fd is not a valid file descriptor. On Unix systems, if the file descriptor is in non-blocking mode, NewFile will attempt to return a pollable File (one for which the SetDeadline methods work).
The only surprising bit to me is that in tun_linux.go we call file.Fd() in both newTun and newTunFromFd. This means that the fd is now in blocking mode, and we continue to use the File object in Nebula... this seems wrong but I haven't heard anyone report hangs on Linux. It's possible that the tun.Write function could be re-written to use SyscallConn, negating the need to call file.Fd in newTun, but I'm not sure what implications this would have.
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Forgive my naive question, but why don't you ask the file descriptor?
res = fcntl (FileFd, F_GETFL)
should return all you need to know; all you have to check is O_NONBLOCK.
Fixes #309.
If no name is specified, the system chooses one. If a name is specified, and the tun exists already, we'll try to use it. If it doesn't exist, we'll rename the one the system gives us.
This could've been done with ifconfig, but I figured this was a good start towards syscalls for FreeBSD.