Re: [PATCH] Add a /proc/self/exedir link

[Bodo Eggert <7eggert@gmx.de>]

On Thu, 6 Apr 2006, Mike Hearn wrote:

> > IMO the program must be aware of the get-my-exedir feature, just configuring
> > --prefix=/proc/... is aiming for your feet.
> 
> I disagree, though /proc/self/exedir may not be the right answer. The 
> problem with the original proposal is there's no concept of a group 
> leader to which files are resolved relative to so there is this problem 
> with child processes.

The problem ist the word 'the'. If parent and child are using 'the foo',
they will clash.

> I sent a mail outlining a scheme that used file descriptor passing to 
> achieve the same effect but with the needed "inheritance" of the path, 
> but, vger seems to have munched it! At least I don't see it on the gmane 
> archives. But the scheme is simple enough:
> 
>   * get_prefix() reads /proc/self/exe and turns it into the correct
>     directory
> 
>   * dup2(open(get_my_exedir()), 999)
>
>   * ./configure --prefix=/proc/self/fd/999

bin/foo calls bin/bar refering to /proc/self/fd/999
bin_2/bar does dup2(open(get_my_exedir()), 999)  ***FUBAR***

possible solution:

don't dup2, and only close fds you opened yourself.

Disadvantage: Leaky (too), may break scripts.

.oO(Can you chroot a single filedescriptor or somehow make 
    /proc/self/fd/$n/.. be unavailable?)

> It also restricts the problem to passing paths to other processes that 
> are not subprocesses (eg via rpc). But as each process can have its own 
> namespace this will always be an issue that needs careful treatment, and 
> the pain of adjusting software to realpath() it is much lower than 
> modifying every path in every piece of software. That approach was 
> already tried and sucks.

There may be no "real path" corresponding to /proc/self/fd/4711.

IMO it's still best to just symlink the program directory to the correct 
place and make the programs search in e.g. ~/opt/ and /opt/.
-- 
Fun things to slip into your budget
An abacus