On 10/19/2014 01:20 PM, Al Viro wrote: > On Fri, Oct 17, 2014 at 02:45:03PM -0700, Andy Lutomirski wrote: > >> For example, I want to be able to reliably do something like nsenter >> --namespace-flags-here toybox sh. Toybox's shell is unusual in that >> it is more or less fully functional, so this should Just Work (tm), >> except that the toybox binary might not exist in the namespace being >> entered. If execveat were available, I could rig nsenter or a similar >> tool to open it with O_CLOEXEC, enter the namespace, and then call >> execveat. > > The question I hadn't seen really answered through all of that was how to > deal with #!... "Just use d_path()" isn't particulary appealing - if that > file has a pathname reachable for you, you could bloody well use _that_ > from the very beginning. > > Frankly, I wonder if it would make sense to provide something like > dupfs. We can't mount it by default on /dev/fd (more's the pity), but > it might be a good thing to have. > > What it is, for those who are not familiar with Plan 9: a filesystem with > one directory and a bunch of files in it. Directory contents depends on > who's looking; for each opened descriptor in your descriptor table, you'll > see two files there. One series is 0, 1, ... - opening one of those gives > dup(). IOW, it's *not* giving you a new struct file; it gives you a new > reference to existing one, complete with sharing IO position, etc. Another > is 0ctl, 1ctl, ... - those are read-only and reading from them gives pretty > much a combination of our /proc/self/fdinfo/n with readlink of /proc/self/fd/n. > > It's actually a better match for what one would expect at /dev/fd than what > we do. Example: > Yes, it is really unfortunate that /proc/self/fd/* had the wrong semantics for the start, due to then-existing implementation issues. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
