[Lxc-users] procfs and unnamed pipes

[Timofey.Kirillov]

06.02.2013 21:48, Serge Hallyn пишет:
> Quoting Timofey.Kirillov (distorhead at gmail.com):
>> Hi,
>>
>> I have a question about using unnamed pipes with procfs.
>>
>> Suppose a chrooted environment with proc mounted as procfs. I am
>> trying to use bash process substitution feature and get this:
>>
>> $ cat <(echo hello)
>> cat: /dev/fd/63: No such file or directory
> works fine for me in a chroot.
>
> My first guess would be that your chroot doesn't have the /dev/fd ->
> /proc/self/fd symlink set up right, though your discussion below
> suggests that's not the case.
>
>> While on the normal system:
>> $ cat <(echo hello)
>> hello
>>
>> As I understand, the problem is that when fuse making getattr on
> Sorry I don't know where fuse comes in.
>
>> file '/dev/fd/63' - it determines that it is symlink. The next step
>> is readlink, which gives something like that: /25977/fd/63 =>
>> pipe:[3087676]. And at the final step getattr on file
>> '/25977/fd/pipe:[3087676]' gives no such file or directory.
>>
>> Actually I encouter this issue while working on similar fuse proc
>> (for jail environments). Then I find procfs, tried it out and get
>> the same failure.
>>
>> I've also tried to change logic of getattr in the next way. First
>> make normal stat of file. If it is not S_ISFIFO - make lstat. In
>> that way the process hangs forever on open syscall:
>> $ strace cat <(echo hello)
>> ...
>> open("/dev/fd/63", O_RDONLY
>>
>>
>> Is there any workaround for this problem?
> I can't reproduce your problem.  Which kernel are you on?
>
> -serge

Thanks for the answer.

I am trying to use this fuse procfs: 
http://lxc.sourceforge.net/download/procfs/

Some system info:
$ uname -a
Linux tp-laptop 3.5.0-18-generic #29-Ubuntu SMP Fri Oct 19 10:26:51 UTC 
2012 x86_64 x86_64 x86_64 GNU/Linux
$ dpkg -l *libfuse*
...
ii libfuse-dev 2.9.0-1ubuntu2 amd64 Filesystem in Userspace (development)
ii libfuse2:amd64 2.9.0-1ubuntu2 amd64 Filesystem in Userspace (library)