Hello Nick,
The GHC runtime system uses alarm signals for a variety of purposes,
and part of this means that your code needs to properly handle
EINTR. Please see:
http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Signals
for more information.
Cheers,
Edward
Excerpts from Nick Rudnick's message of Sat Apr 28 07:21:30 -0400 2012:
> Dear all,
>
> after noticing problems with libssh2, and trying to fix this myself, I ran
> into a strange experience which I wish to get an explanation for.
>
> After compiling an OpenSSH server and a raw C libssh2 (for comparison) with
> debug messaging, I with support of the libssh2 community was able to trace
> the problem back to a call to poll(3) in session.c::_libssh2_wait_socket(),
>
> rc = poll(sockets, 1, has_timeout?ms_to_next: -1);
>
> where sockets consists of a single socket, session->socket_fd.
>
> This is roughly a polling with timeout for the connection – and, with the
> Haskell FFI, an
>
> error 4 / EINTR / Interrupted system call
>
> is thrown, and I was explained that this probably is caused by another
> signal of the same code unit. Not finding anything, I at the end extended
> libssh2 by a function,
>
> LIBSSH2_API void libssh2_test(void){
> struct sockaddr_in sin;
> LIBSSH2_SESSION *session;
> const char *fingerprint;
> LIBSSH2_CHANNEL *channel;
> const unsigned long hostaddr= htonl(0x7F000001);
> const char *username= "i";
> const char *keyfile1="/home/i/.ssh/id_rsa.pub";
> const char *keyfile2="/home/i/.ssh/id_rsa";
> const char *password= "D0r1nha23";
> int got= 0;
> int sock= socket(AF_INET, SOCK_STREAM, 0);
> sin.sin_family= AF_INET;
> sin.sin_port= htons(22);
> sin.sin_addr.s_addr= hostaddr;
> if(connect( sock, (struct sockaddr*)(&sin), sizeof(struct sockaddr_in)
> ) != 0 ) {
> fprintf(stderr, "failed to connect!\n");
> return;
> }
> session= libssh2_session_init();
> libssh2_trace(session,~0);
> if(libssh2_session_handshake(session, sock)) {
> _libssh2_debug(session, LIBSSH2_TRACE_TRANS
> , "Failure establishing SSH session" );
> return;
> }
> fingerprint= libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_SHA1);
> libssh2_userauth_list(session, username, strlen(username)); // ??
> if(libssh2_userauth_publickey_fromfile( session
> , username
> , keyfile1
> , keyfile2
> , password )) {
> _libssh2_debug(session, LIBSSH2_TRACE_TRANS
> , "\tAuthentication by public key failed!" );
> return;
> } else {
> _libssh2_debug( session, LIBSSH2_TRACE_TRANS
> , "\tAuthentication by public key succeeded." );
> if(!(channel= libssh2_channel_open_session(session))) {
> _libssh2_debug( session, LIBSSH2_TRACE_TRANS
> , "Unable to open a session" );
> return;
> } else {
> libssh2_channel_setenv(channel, "FOO", "bar");
> if(libssh2_channel_request_pty(channel, "vanilla")) {
> _libssh2_debug( session, LIBSSH2_TRACE_TRANS
> , "Failed requesting pty" );
> } else {
> if(libssh2_channel_shell(channel)) {
> _libssh2_debug( session, LIBSSH2_TRACE_TRANS
> , "Unable to request shell on allocated pty" );
> } else {
> if(channel){
> libssh2_channel_free(channel);
> channel= NULL;
> }
> }
> }
> }
> }
> libssh2_session_disconnect( session
> , "Normal Shutdown, Thank you for playing" );
> libssh2_session_free(session);
> close(sock);
> libssh2_exit();
> return;
> }
>
> and called it by
>
> foreign import ccall unsafe "libssh2_test"
> libssh2Test:: IO ()
>
> as well as
>
> {# context lib="ssh2" prefix="libssh2" #}
> {# fun test as test { } -> `()' #}
>
> With both approaches, I still got the same EINTR error, while coalling
> libssh2_test() from C works completely flawless.
>
> Is it possible that an interfering signal comes from the FFI? If yes, is
> there a workaround?
>
> Grateful for any kind of enlightenment... :-)
>
> Thanks a lot in advance, Nick
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