int bindresvport(int sockfd, struct sockaddr_in *sin);
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.
If the bind(2) performed by bindresvport() is successful, and sin is
not NULL, then sin->sin_port returns the port number actually allo-
sin can be NULL, in which case sin->sin_family is implicitly taken to
be AF_INET. However, in this case, bindresvport() has no way to return
the port number actually allocated. (This information can later be
obtained using getsockname(2).)
bindresvport() returns 0 on success; otherwise -1 is returned and errno
set to indicate the cause of the error.
bindresvport() can fail for any of the same reasons as bind(2). In
addition, the following errors may occur:
EACCES The caller did not have superuser privilege (to be precise: the
CAP_NET_BIND_SERVICE capability is required).
All privileged ports are in use.
EAFNOSUPPORT (EPFNOSUPPORT in glibc 2.7 and earlier)
sin is not NULL and sin->sin_family is not AF_INET.
Multithreading (see pthreads(7))
Before glibc 2.17, the bindresvport() function uses a static variable
that is not protected, so it is not thread-safe.
Since glibc 2.17, the bindresvport() function uses a lock to protect
static variable, so it is thread-safe.
Not in POSIX.1-2001. Present on the BSDs, Solaris, and many other sys-
Unlike some bindresvport() implementations, the glibc implementation
ignores any value that the caller supplies in sin->sin_port.
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