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List:       linux-kernel
Subject:    Re: [RFC][PATCH] scripts with stdin replaced
From:       Jamie Lokier <lkd () tantalophile ! demon ! co ! uk>
Date:       1999-07-05 16:11:53
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We don't want to be rewriting any interpreters.  New options are not an
option (as it were).

Richard Guenther wrote:
> >   - Open fd 3, pass /proc/self/fd/3 as the script name.
> 
> And rewrite each program to _not_ open("/proc/self/fd/3") as
> this is just a symlink to the real file, i.e. I could have passed
> the filename right away.

No, /proc/self/fd/3 is not an ordinary symlink although it looks like
one to `ls'.  It always reopens the correct file.  Programs do not have
to be changed, and it doesn't have the same race condition as passing
the filename.

> stdin replacement seems the only way to deal with this _without_
> rewriting the interpreters to know about /proc/self/script.

Why would the interpreters need rewriting?

> [I could just add an option to interpreter to take a fd as argument
> anyway]
> 
> >   - Pass /proc/self/script as the script name and add code to proc
> >     to support this -- this provides the interpreter with fds 0,1 & 2
> >     as the only open ones which it may be expecting.
> 
> see above. of course, with appropriate /proc/self/script that handles
> open() just fine (in fact ignores the open and just returns the fd)
> this would be fine.

> Implementation would be ugly though. How (where)
> do you pass the information to /proc? (that 3 is the script fd)
> Probably you have to add this to struct task?

The point of /proc/self/script is that no fd is allocated until it is
opened -- for interpreters that expect the next free fd to be number 3.
Yes I would add it to struct task.

> or just reserve fd number 3 for this and nothing else (would this
> break any userspace semantics?  i.e. open() never returns fd 3, fd 3
> is reserved for script passing only).

If you're going to reserve fd number 3, /proc/self/fd/3 is exactly the
right way to refer to this.  Of course opening it returns fd 4, but
that's not so bad is it?

-- Jamie

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