Hi Mats,
I fixed the page after Petr's comments, and also added a note to
explicitly say that the implementation doesn't use sin->sin_port.
Revised version of the page below.
Cheers,
Michael
.\" Copyright (C) 2007, Michael Kerrisk <mtk.manpages@xxxxxxxxx>
.\" and Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@xxxxxxxxx>
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.\" 2007-05-31, mtk: Rewrite and substantial additional text.
.\" 2008-12-03, mtk: Rewrote some pieces and fixed some errors
.\"
.TH BINDRESVPORT 3 2008-12-03 "" "Linux Programmer's Manual"
.SH NAME
bindresvport \- bind a socket to a privileged IP port
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <netinet/in.h>
.LP
.BI "int bindresvport(int " sockfd ", struct sockaddr_in *" sin );
.fi
.SH DESCRIPTION
.LP
.BR bindresvport ()
is used to bind a socket descriptor to a privileged anonymous IP port,
that is, a port number arbitrarily selected from the range 512 to 1023.
.\" Glibc actually starts searching with a port # in the range 600 to 1023
If the
.BR bind (2)
performed by
.BR bindresvport ()
is successful, and
.I sin
is not NULL, then
.I sin\->sin_port
returns the port number actually allocated.
.I sin
can be NULL, in which case
.I sin\->sin_family
is implicitly taken to be
.BR AF_INET .
However, in this case,
.BR bindresvport ()
has no way to return the port number actually allocated.
(This information can later be obtained using
.BR getsockname (2).)
.SH RETURN VALUE
.BR bindresvport ()
returns 0 on success; otherwise \-1 is returned and
.I errno
set to indicate the cause of the error.
.SH ERRORS
.BR bindresvport ()
can fail for any of the same reasons as
.BR bind (2).
In addition, the following errors may occur:
.TP
.BR EACCES
The caller did not have superuser privilege (to be precise: the
.B CAP_NET_BIND_SERVICE
capability is required).
.TP
.B EADDRINUSE
All privileged ports are in use.
.TP
.BR EAFNOSUPPORT " (" EPFNOSUPPORT " in glibc 2.7 and earlier)"
.I sin
is not NULL and
.I sin->sin_family
is not
.BR AF_INET .
.SH "CONFORMING TO"
Not in POSIX.1-2001.
Present on the BSDs, Solaris, and many other systems.
.SH NOTES
Unlike some
.BR bindresvport ()
implementations,
the glibc implementation ignores any value that the caller supplies in
.IR sin\->sin_port .
.SH SEE ALSO
.BR bind (2),
.BR getsockname (2)
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