Re: [PATCH] [hurd] pflocal/socket.c: Support MSG_DONTWAIT in pflocal send/recv

[Justus Winter]

Christian Seiler <christian@iwakd.de> writes:

>>>> Use the remap translator instead, which is one of the things the Hurd
>>>> design allows you to do easily.
>>>>
>>>> See /bin/remap to easily set one.
>>>
>>> remap doesn't work at all here, programs then complain
>>> that they can't assign requested address when doing any
>>> socket operation.
>> 
>> Seems to work fine here:
>> 
>> teythoon@hurdbox ~ % cd /tmp
>> teythoon@hurdbox /tmp % settrans -ac 1 /hurd/pflocal
>> teythoon@hurdbox /tmp % remap /servers/socket/1 /tmp/1 -- /bin/bash -c 'echo 
>> huhu world | wc'
>>       1       2      11
>
> For pipes yes, for named sockets (which is what open-isns
> uses): no.
>
> $ cd /tmp
> $ settrans -ac 1 /hurd/pflocal
> $ remap /servers/socket/1 /tmp/1 -- python3
> Python 3.5.2+ (default, Aug  5 2016, 08:07:14) 
> [GCC 6.1.1 20160705] on gnu0
> Type "help", "copyright", "credits" or "license" for more information.
>>>> import socket
>>>> s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
>>>> s.bind('/tmp/test.sock')
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> OSError: [Errno 1073741873] Cannot assign requested address
>
> (Same also from C programs, Python is just easier to test.)
>
> The same python code works if you run it without remap.

Right, I can see how this is a problem.  The thing is, remap doesn't
quite do the job: 1/ it fails to remap relative paths, 2/ if one sets a
translator record on a node, and that translator is then started by the
filesystem, it is started "outside" of the remap environment.  I belive
2/ is what happens here.

fakeroot has the same problem.  For me, lack of robust lightweight
virtualization this is the most pressing shortcoming of the Hurd, and I
did some work to address this.  Aiui remap/fakeroot must prevent the
filesystem from starting the translator and do it themself to make the
translation more correct.

> Anyway, not terribly important to me, rebooting did work fine
> anyway, and I now have a working patch for open-isns that will
> make it work on Hurd once my other patch against pflocal's
> socket.c is merged.

Cool!

Cheers,
Justus

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