Rationale for paccept() sigset argument?

[Michael Kerrisk]

Ulrich,

I'll need to cover this point in the man pages, and the rationale still isn't
clear to me, so I'll check it with you...

2.6.27-rc has paccept():

int paccept(int fd, struct sockaddr *sockaddr, socklen_t *addrlen,
        const sigset_t *sigmask, int setsize, int flags)

paccept() blocks until either a connection is received on fd, or a signal is
sigmask() is caught.

What is the rationale for the sigset argument of paccept()?

For pselect()/ppoll()/epoll_pwait(), the sigset argument allows us to deal
with a not uncommon situation: waiting for both signals and (multiple) file
descriptors.  (The alternative is the self-pipe trick, which requires more
programming effort.)

However, do we really need this argument for paccept()?  I ask this for the
following reasons:

* This seems to be special casing for accept().  But there are other system
calls (e.g., open(), connect(), recvfrom()) that are similar, in the sense
that they may wait on a file descriptor, for which there is no [perceived
need for a] sigset argument.

* It seems to me that any case where we might want to use paccept() could be
equivalently dealt with using the existing pselect()/ppoll()/epoll_pwait()
followed by a conventional accept() if the listening file descriptor
indicates as ready.  (But perhaps I missed something?)

Can you please explain why we need this special case for [p]accept()?

Cheers,

Michael


--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html

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