How to get the list of all my open file(descriptor)s and locks?

Ismael Farfán

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Sep 19, 2012, 1:34:25 PM9/19/12

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Hello list

>From man 2 EXECVE
"By default, file descriptors remain open across an execve()"

And from man 2 FCNTL
"Record locks are... preserved across an execve(2)."

So the question:
* If I execve a python script (from C), how can I retrieve the list of
files, and optionally the list of locks, from within the execve(d)
python process so that I can use them?

Some more info:
I'm working with exotic stuff like AIX and Solaris 10 (Windows and
linux too :) and my lowest common denominator is python 2.3.

>From a standalone test within the interpreter I'd expect to get (at
least) std(in/out/err).

If more information is needed in order to help me, please let me know.

Cheers
Ismael

--
Do not let me induce you to satisfy my curiosity, from an expectation,
that I shall gratify yours. What I may judge proper to conceal, does
not concern myself alone.

Ismael Farfán

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Sep 19, 2012, 4:36:02 PM9/19/12

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2012/9/19 Ismael Farfán <sulf...@gmail.com>:

It seems like I can use os.fstat to find out if a fd exists and also
get it's type and mode (I'm getting some pipes too : )

I hope it's portable across platforms, if someone knows a better
solution please let me know.

Ian Kelly

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Sep 19, 2012, 5:09:47 PM9/19/12

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On Wed, Sep 19, 2012 at 11:34 AM, Ismael Farfán <sulf...@gmail.com> wrote:
> So the question:
> * If I execve a python script (from C), how can I retrieve the list of
> files, and optionally the list of locks, from within the execve(d)
> python process so that I can use them?
>
>
> Some more info:
> I'm working with exotic stuff like AIX and Solaris 10 (Windows and
> linux too :) and my lowest common denominator is python 2.3.

You could do:

os.listdir("/proc/%d/fd" % os.getpid())

This should work on Linux, AIX, and Solaris, but obviously not on Windows.

Ian Kelly

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Sep 19, 2012, 5:40:11 PM9/19/12

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On Wed, Sep 19, 2012 at 2:36 PM, Ismael Farfán <sulf...@gmail.com> wrote:
> It seems like I can use os.fstat to find out if a fd exists and also
> get it's type and mode (I'm getting some pipes too : )

Sure, because files and pipes both use the file descriptor
abstraction. If your process does any networking, you'll find sockets
in there as well.

Ismael Farfán

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Sep 19, 2012, 5:58:56 PM9/19/12

to Ian Kelly, Python

2012/9/19 Ian Kelly <ian.g...@gmail.com>:

> --
> http://mail.python.org/mailman/listinfo/python-list

Seems like things will get interesting :D

Christian Heimes

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Sep 19, 2012, 8:39:42 PM9/19/12

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Am 19.09.2012 19:34, schrieb Ismael Farfán:
> Hello list
>
> From man 2 EXECVE
> "By default, file descriptors remain open across an execve()"
>
> And from man 2 FCNTL
> "Record locks are... preserved across an execve(2)."
>

> So the question:
> * If I execve a python script (from C), how can I retrieve the list of
> files, and optionally the list of locks, from within the execve(d)
> python process so that I can use them?

Have a look at psutil:

http://code.google.com/p/psutil/#Process_management

Christian

Chris Angelico

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Sep 19, 2012, 11:11:11 PM9/19/12

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On Thu, Sep 20, 2012 at 7:09 AM, Ian Kelly <ian.g...@gmail.com> wrote:
> You could do:
>
> os.listdir("/proc/%d/fd" % os.getpid())
>
> This should work on Linux, AIX, and Solaris, but obviously not on Windows.

I'm not sure how cross-platform it is, but at least on Linux, you can
use /proc/self as an alias for "/proc/"+os.getpid() - worth a try,
might make your code a bit easier to read.

It's documented as useful when you don't know the PID yet (eg telling
a process to read the file /proc/self/fd/0 to force it to use stdin).
So I'm confident enough to recommend testing it. :)

ChrisA

Ismael Farfán

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Sep 20, 2012, 12:21:25 AM9/20/12

to Christian Heimes, pytho...@python.org

2012/9/19 Christian Heimes <chri...@python.org>:

>> So the question:
>> * If I execve a python script (from C), how can I retrieve the list of
>> files, and optionally the list of locks, from within the execve(d)
>> python process so that I can use them?
>
> Have a look at psutil:
>
> http://code.google.com/p/psutil/#Process_management
>
> Christian
>

> --
> http://mail.python.org/mailman/listinfo/python-list

Unfortunately I'm not allowed to install 3rd party SW unless it's
absolutely necessary, but thanks for sharing, I'll have a look at the
arch dependent code : )

Hans Mulder

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Sep 20, 2012, 4:30:30 AM9/20/12

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On 20/09/12 05:11:11, Chris Angelico wrote:
> On Thu, Sep 20, 2012 at 7:09 AM, Ian Kelly <ian.g...@gmail.com> wrote:
>> You could do:
>>
>> os.listdir("/proc/%d/fd" % os.getpid())
>>
>> This should work on Linux, AIX, and Solaris, but obviously not on Windows.

On MacOS X, you can use

os.listdir("/dev/fd")

This might work on other OSes.

> I'm not sure how cross-platform it is, but at least on Linux, you can
> use /proc/self as an alias for "/proc/"+os.getpid() - worth a try,
> might make your code a bit easier to read.
>
> It's documented as useful when you don't know the PID yet (eg telling
> a process to read the file /proc/self/fd/0 to force it to use stdin).

At least on Linux, Solaris and MacOS X, you shouldd use /dev/stdin,
which is a symlink to whatever the official name is.
"/dev/stdin" is more readable and more portable than the official name.

> So I'm confident enough to recommend testing it. :)

Testing such things is the best way to learn.

Hope this helps,

-- HansM