--stderr=/dev/fd/1 doesn't work

[seirl]

The workaround for piping stderr to stdout suggested here: f7b60f2

doesn't seem to work:

$ isolate --box-id 0 --cg -p --stderr=/dev/fd/1 --stdout=stdout --run -- /bin/bash -c "echo a >&2; echo b; echo a >&2; echo b"     
OK (0.000 sec real, 0.019 sec wall)
$ cat /var/lib/isolate/0/box/stdout 
b
b

Any idea why that is the case?

[zopieux]

@gollux any idea or workaround? Thanks!

[gollux]

In fact, it works, but in a somewhat unexpected way: you really get both fd 1 and fd 2 pointing to the same file, but each fd has its own position in the file, so the echo'ed strings are overwriting one another.

Cloning the fd would have more sense, wouldn't it?

[seirl]

Cloning the fd would have more sense, wouldn't it?

That's what the code was doing before, yeah, but now I'm not sure what would be a good way to have the same feature again from the outside, especially with all the permission/setuid stuff that prevent us from opening /box files from the caller.

[gollux]

I just added a --stderr-to-stdout switch, which asks for the old default behavior.

I was thinking about adding a generic file redirection mechanism, but I failed to find any nice syntax for that. Nor did I find any other applications.

[seirl]

This is great, I'll try that as soon as possible! This mirrors the API we have in https://github.com/prologin/camisole/blob/master/camisole/isolate.py#L171 . The use case is when we have a single display and we want to preserve the timing of the logging, so we can't just concatenate the outputs. I also can't think of an use case for redirecting other files/fds so I think the current patch is exactly what was needed.

Thanks a lot!