* Linus Torvalds <[EMAIL PROTECTED]> wrote: > > I agree. What would be a good interface to allocate fds in such > > area? We don't want to replicate syscalls, so maybe a special new > > dup function? > > I'd do it with something like "newfd = dup2(fd, NONLINEAR_FD)" or > similar, and just have NONLINEAR_FD be some magic value (for example, > make it be 0x40000000 - the bit that says "private, nonlinear" in the > first place). > > But what's gotten lost in the current discussion is that we probably > don't actually _need_ such a private space. I'm just saying that if > the *choice* is between memory-mapped interfaces and a private > fd-space, we should probably go for the latter. "Everything is a file" > is the UNIX way, after all. But there's little reason to introduce > private fd's otherwise.
it's both a flexibility and a speedup thing as well: flexibility: for libraries to be able to open files and keep them open comes up regularly. For example currently glibc is quite wasteful in a number of common networking related functions (Ulrich, please correct me if i'm wrong), which could be optimized if glibc could just keep a netlink channel fd open and could poll() it for changes and cache the results if there are no changes (or something like that). speedup: i suggested O_ANY 6 years ago as a speedup to Apache - non-linear fds are cheaper to allocate/map: http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg23820.html (i definitely remember having written code for that too, but i cannot find that in the archives. hm.) In theory we could avoid _all_ fd-bitmap overhead as well and use a per-process list/pool of struct file buffers plus a maximum-fd field as the 'non-linear fd allocator' (at the price of only deallocating them at process exit time). Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
