[9fans] Passing a file descriptor between processes

[9fans] Passing a file descriptor between processes

[Kirill A. Shutemov]

One of the ugliest interface in Unix is passing a file descriptor between
processes [1]. Does Plan9 provide any mechanism for it?

[1] http://book.chinaunix.net/special/ebook/addisonWesley/APUE2/0201433079/ch17lev1sec4.html

--
 Kirill A. Shutemov

Re: [9fans] Passing a file descriptor between processes

[Lucio De Re]

On Fri, Nov 05, 2010 at 12:29:46PM +0200, Kirill A. Shutemov wrote:
>
> One of the ugliest interface in Unix is passing a file descriptor between
> processes [1]. Does Plan9 provide any mechanism for it?
>
You can pass fds in channels between threads, but for processes you
should look at #s for guidance.

++L

Re: [9fans] Passing a file descriptor between processes

[erik quanstrom]

On Fri Nov  5 06:32:55 EDT 2010, kirill@shutemov.name wrote:
> One of the ugliest interface in Unix is passing a file descriptor between
> processes [1]. Does Plan9 provide any mechanism for it?
>
> [1] http://book.chinaunix.net/special/ebook/addisonWesley/APUE2/0201433079/ch17lev1sec4.html

there is no mechanism similar to sending fds over a socket.
the two ways of file descriptor sharing are via
(a) rfork(2); and
(b) srv(3)

rfork (optionally) allows a process to share a file descriptor
table with a child process.  srv allows a process to post a file
descriptor by a given name in /srv.  the normal file operations
apply on that file.  in particular, it must be opened
before use.

- erik

Re: [9fans] Passing a file descriptor between processes

[roger peppe]

see srv(3)
http://plan9.bell-labs.com/magic/man2html/3/srv

On 5 November 2010 10:29, Kirill A. Shutemov <kirill@shutemov.name> wrote:
> One of the ugliest interface in Unix is passing a file descriptor between
> processes [1]. Does Plan9 provide any mechanism for it?
>
> [1] http://book.chinaunix.net/special/ebook/addisonWesley/APUE2/0201433079/ch17lev1sec4.html
>
> --
>  Kirill A. Shutemov
>
>

Re: [9fans] Passing a file descriptor between processes

[erik quanstrom]

On Fri Nov  5 07:36:42 EDT 2010, rogpeppe@gmail.com wrote:
> see srv(3)
> http://plan9.bell-labs.com/magic/man2html/3/srv
>
> On 5 November 2010 10:29, Kirill A. Shutemov <kirill@shutemov.name> wrote:
> > One of the ugliest interface in Unix is passing a file descriptor between
> > processes [1]. Does Plan9 provide any mechanism for it?
> >
> > [1] http://book.chinaunix.net/special/ebook/addisonWesley/APUE2/0201433079/ch17lev1sec4.html

the op may have seen this: http://lwn.net/Articles/411845/
—which i found hard to read because the author's changing
definition of "unix".

- erik

Re: [9fans] Passing a file descriptor between processes

[Venkatesh Srinivas]

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On Fri, Nov 5, 2010 at 7:41 AM, erik quanstrom <quanstro@labs.coraid.com>wrote:

> On Fri Nov  5 07:36:42 EDT 2010, rogpeppe@gmail.com wrote:
> > see srv(3)
> > http://plan9.bell-labs.com/magic/man2html/3/srv
> >
> > On 5 November 2010 10:29, Kirill A. Shutemov <kirill@shutemov.name>
> wrote:
> > > One of the ugliest interface in Unix is passing a file descriptor
> between
> > > processes [1]. Does Plan9 provide any mechanism for it?
> > >
> > > [1]
> http://book.chinaunix.net/special/ebook/addisonWesley/APUE2/0201433079/ch17lev1sec4.html
>
> the op may have seen this: http://lwn.net/Articles/411845/
> —which i found hard to read because the author's changing
> definition of "unix".
>
> - erik
>
>
There was a discussion here a while ago about it too: search for 'sendfd on
native Plan 9' from december 2008. Start here:
http://9fans.net/archive/2008/12/515, follow till January 2009.

Currently, if your processes have a common parent, you can use rfork; if
not, you must resort to #s. '#s' is a pretty unfortunate interface,
though...

-- vs

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Re: [9fans] Passing a file descriptor between processes

[erik quanstrom]

> Currently, if your processes have a common parent, you can use rfork; if
> not, you must resort to #s. '#s' is a pretty unfortunate interface,
> though...

okay, practicially speaking, what's wrong with #s, and what do you propose?

- erik

Re: [9fans] Passing a file descriptor between processes

[Lucio De Re]

On Fri, Nov 05, 2010 at 08:16:30AM -0400, Venkatesh Srinivas wrote:
>
> '#s' is a pretty unfortunate interface,
> though...
>
Maybe.  But it is only a tool and as such it can be replaced or augmented.
It's unlikely that Plan 9 will retain its integrity without #s, but
that does not mean that an alternative can't be installed with similar,
but more friendly semantics.  Hm, let me try this: it means that an
alternative can be installed, more suitable to a slightly different
application.  It does need to be a kernel device.

++L

Re: [9fans] Passing a file descriptor between processes

[Skip Tavakkolian]

i wish #s had a directory structure and enforced group permissions.

On Fri, Nov 5, 2010 at 5:21 AM, erik quanstrom <quanstro@quanstro.net> wrote:
>> Currently, if your processes have a common parent, you can use rfork; if
>> not, you must resort to #s. '#s' is a pretty unfortunate interface,
>> though...
>
> okay, practicially speaking, what's wrong with #s, and what do you propose?
>
> - erik
>
>