Re: [PATCH] Futex Asynchronous Interface

[Peter W鋍htler]

Linus Torvalds schrieb:
> 
> On Fri, 7 Jun 2002, Peter W鋍htler wrote:
> >
> > What about /proc/futex then?
> 
> Why?
> 
> Tell me _one_ advantage from having the thing exposed as a filename?
> 

There is no enforcing advantage for this.

newbie question: how to provide file operations like poll
without an entry in the filesystem? (in the meantime I will try
to answer this myself :)

> The whole point with "everything is a file" is not that you have some
> random filename (indeed, sockets and pipes show that "file" and "filename"
> have nothing to do with each other), but the fact that you can use common
> tools to operate on different things.
> 
> But there's absolutely no point in opening /dev/futex from a shell script
> or similar, because you don't get anything from it. You still have to bind
> the fd to it's real object.
> 
> In short, the name "/dev/futex" (or "/proc/futex") is _meaningless_.
> There's no point to it. It has no life outside the FUTEX system call, and
> the only thing that you can do by exposing it as a name is to cause
> problems for people who don't want to mount /proc, or who do not happen to
> have that device node in their /dev.
> 
> > Give it an entry in the namespace, why not with sockets (unix and ip) also?
> 
> Perhaps because you cannot enumerate sockets and pipes? They don't _have_
> names before they are created. Same as futexes, btw.
> 

Still you can open a file in the namespace and write some commands to it.
Then it turns out to be a socket on port 25:

fd=open("/dev/socket",O_RDWR);
write(fd,"connect stream 25\n",sizeof(..));
write(fd,"helo mail.my.com\n",..);
...

Just one more question: would it be possible to specify a poll operation
for /proc/blah?