Provided by: libssl-doc_1.0.1f-1ubuntu2.27_all 
NAME
SSL_get_fd - get file descriptor linked to an SSL object
SYNOPSIS
#include <openssl/ssl.h>
int SSL_get_fd(const SSL *ssl);
int SSL_get_rfd(const SSL *ssl);
int SSL_get_wfd(const SSL *ssl);
DESCRIPTION
SSL_get_fd() returns the file descriptor which is linked to ssl. SSL_get_rfd() and SSL_get_wfd() return
the file descriptors for the read or the write channel, which can be different. If the read and the write
channel are different, SSL_get_fd() will return the file descriptor of the read channel.
RETURN VALUES
The following return values can occur:
-1 The operation failed, because the underlying BIO is not of the correct type (suitable for file
descriptors).
>=0 The file descriptor linked to ssl.
SEE ALSO
SSL_set_fd(3), ssl(3) , bio(3)