On Thu, 8 Mar 2007, Davide Libenzi wrote:
>
> So, to cut it short, I can do the pseudo-siginfo read(2), but I don't
> like it too much (little, actually). The siginfo, as bad as it is, is a
> standard used in many POSIX APIs (hence even in kernel), and IMO if we
> want to send that back, a struct siginfo should be.
> No?
I think it's perfectly fine if you make it "struct siginfo" (even though I
think it's a singularly ugly struct). It's just that then you'd have to
make your read() know whether it's a compat-read or not, which you really
can't.
Which is why you introduced a new system call, but that leads to all the
problems with the file descriptor no longer being *usable*.
Think scripts. It's easy to do reads in perl scripts, and parse the
output. In contrast, making perl use a new system call is quite
challenging.
And *that* is why "everything is a stream of bytes" is so important. You
don't know where the file descriptor has been, or who uses it. Special
system calls for special file descriptors are just *wrong*.
After all, that's why we'd have a signalfd() in the first place: exactly
so that you do *not* have to use special system calls, but can just pass
it on to any event waiting mechanism like select, poll, epoll. The same is
just *even*more*true* when it comes to reading the data!
Linus
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