[Bug 258056] lang/go118: musn't poll /dev/fuse

From: <bugzilla-noreply_at_freebsd.org>
Date: Tue, 09 Aug 2022 08:05:10 UTC

Yuval Pavel Zholkover <paulzhol@gmail.com> changed:

           What    |Removed                     |Added
                 CC|                            |paulzhol@gmail.com

--- Comment #26 from Yuval Pavel Zholkover <paulzhol@gmail.com> ---
Created attachment 235792
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=235792&action=edit
bazil/fuse workaround


As I mentioned in the upstream issue https://github.com/golang/go/issues/54100,
there are a few issues here.

The Go runtime has a bug in which file descriptors in blocking mode can get
added to the network poller. This is what the
https://go-review.googlesource.com/c/go/+/420334 fix is about.

However I think there's an additional bug in the /dev/fuse character device:
The call to fcntl(<fd>,F_SETFL,O_RDWR|O_NONBLOCK) is reporting an ENODEV
(Operation not supported by device) error, but the device is still put into
non-blocking mode. Causing reads to return EAGAIN.
These EAGAIN errors are unexpected by the bazil/fuse package rclone uses.

bazil/fuse is doing blocking operations only anyway, so there's a simple
workaround which avoids calling fcntl in the first place (attached).

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