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SubjectRe: Signal handling different for root and others
Andi Kleen wrote:
> On Tue, Sep 12, 2000 at 02:20:02AM +0200, jury gerold wrote:
> > I ran into a problem with 2.2.x kernels, posix signals and sockets.
> >
> > I have a program that creates a serversocket, puts it into listen state,
> > attaches the socket to a realtime signal and simply waits for the signal.
> >
> > When i create a connection (telnet a.b.c.d port) the signal is delivered depending
> > on the user that does the telnet.
> > If root creates the socket, then only root or another machine is able to trigger the signal
> > by connecting to the socket.
> > Normal users are only able to create a SIGIO signal when connecting.
> That's very unlikely. TCP does not propagate gid/uid information over sockets,
> not even over localhost.
> There was probably some other factor during your tests. When you overflow
> the rt signal queue then the kernel will fall back to sending SIGIO. In
> this case you have to collect outstanding events using poll.
> -Andi
> -

Thats right. A connection from a different machine always triggers the realtime signal.
On the same machine however, it depends on the user that does the connect and on the
user that creates the listening socket.

While you mention it : Somewhere in net/socket.c there is a connection between SIGIO and SO_NOSPACE.

int sock_wake_async(struct socket *sock, int how)

I am trying to follow the code, but it's a little bit difficult for me.

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