Re: FMODE_EXEC or alike?

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Mon, 2006-02-20 at 21:51 -0800, Andrew Morton wrote:
> Oleg Drokin <green@linuxhacker.ru> wrote:
> >
> > Hello!
> > 
> >    We are working on a lustre client that would not require any patches
> >    to linux kernel. And there are few things that would be nice to have
> >    that I'd like your input on.
> > 
> >    One of those is FMODE_EXEC - to correctly detect cross-node situations with
> >    executing a file that is opened for write or the other way around, we need
> >    something like this extra file mode to be present (and used as a file open
> >    mode when opening files for exection, e.g. in fs/exec.c)
> >    Do you think there is a chance this can be included into vanilla kernel,
> >    or is there a better solution I oversee?
> >    I am just thinking about something as simple as this
> >    (with some suitable FMODE_EXEC define, of course):
> > 
> > --- linux/fs/exec.c.orig	2006-02-21 00:11:47.000000000 +0200
> > +++ linux/fs/exec.c	2006-02-21 00:12:24.000000000 +0200
> > @@ -127,7 +127,7 @@ asmlinkage long sys_uselib(const char __
> >  	struct nameidata nd;
> >  	int error;
> >  
> > -	error = __user_path_lookup_open(library, LOOKUP_FOLLOW, &nd, FMODE_READ);
> > +	error = __user_path_lookup_open(library, LOOKUP_FOLLOW, &nd, FMODE_READ|FMODE_EXEC);
> >  	if (error)
> >  		goto out;
> >  
> > @@ -477,7 +477,7 @@ struct file *open_exec(const char *name)
> >  	int err;
> >  	struct file *file;
> >  
> > -	err = path_lookup_open(name, LOOKUP_FOLLOW, &nd, FMODE_READ);
> > +	err = path_lookup_open(name, LOOKUP_FOLLOW, &nd, FMODE_READ|FMODE_EXEC);
> >  	file = ERR_PTR(err);
> >  
> >  	if (!err) {
> > 
> 
> Such a patch would have zero runtime cost.  I'd have no problem carrying
> that if it makes things easier for lustre, personally.
> 
> We would need to understand whether this is needed by other distributed
> filesystems and if so, whether the proposed implementation is suitable and
> sufficient.

Hmm.... We might possibly want to use that for NFSv4 at some point in
order to deny write access to the file to other clients while it is in
use.

Cheers
  Trond