First steps in make signals more abstract from the underlying mechanism; replace epoll with poll.

We now don't assume that a signal equals a single fd (eventfd on Linux).
The next step would be to create a version of signal.c that uses a pipe
internally, so it can be used on other platforms, like *BSD.

This is also the reason epoll was replaced with poll in uplink.c

2 files changed, 52 insertions, 21 deletions

diff --git a/src/shared/signal.c b/src/shared/signal.c
index a0697f8..e023c49 100644
--- a/src/shared/signal.c
+++ b/src/shared/signal.c
@@ -5,25 +5,38 @@
 #include <errno.h>
 #include <unistd.h>
 
-int signal_new()
+/*
+ * Linux implementation of signals.
+ * Internally, eventfds are used for signalling, as they
+ * provide the least overhead. We don't allocate any struct
+ * ever, but cast the event fd+1 to dnbd3_signal_t*
+ * to save all the malloc() and free() calls.
+ */
+
+dnbd3_signal_t* signal_new()
 {
-	return eventfd( 0, EFD_NONBLOCK );
+	// On error, eventfd() returns -1, so essentially we return NULL on error.
+	// (Yes, NULL doesn't have to be 0 everywhere, but cmon)
+	return (dnbd3_signal_t*)(intptr_t)( eventfd( 0, EFD_NONBLOCK ) + 1 );
 }
 
-int signal_newBlocking()
+dnbd3_signal_t* signal_newBlocking()
 {
-	return eventfd( 0, 0 );
+	return (dnbd3_signal_t*)(intptr_t)( eventfd( 0, 0 ) + 1 );
 }
 
-int signal_call(int signalFd)
+int signal_call(const dnbd3_signal_t* const signal)
 {
-	if ( signalFd < 0 ) return 0;
+	if ( signal == NULL ) return SIGNAL_ERROR;
 	static uint64_t one = 1;
+	const int signalFd = ( (int)(intptr_t)signal ) - 1;
 	return write( signalFd, &one, sizeof one ) == sizeof one;
 }
 
-int signal_wait(int signalFd, int timeoutMs)
+int signal_wait(const dnbd3_signal_t* const signal, int timeoutMs)
 {
+	if ( signal == NULL ) return SIGNAL_ERROR;
+	const int signalFd = ( (int)(intptr_t)signal ) - 1;
 	struct pollfd ps = {
 		.fd = signalFd,
 		.events = POLLIN
@@ -32,12 +45,14 @@ int signal_wait(int signalFd, int timeoutMs)
 	if ( ret == 0 ) return SIGNAL_TIMEOUT;
 	if ( ret == -1 ) return SIGNAL_ERROR;
 	if ( ps.revents & ( POLLERR | POLLNVAL ) ) return SIGNAL_ERROR;
-	return signal_clear( signalFd );
+	return signal_clear( signal );
 }
 
-int signal_clear(int signalFd)
+int signal_clear(const dnbd3_signal_t* const signal)
 {
+	if ( signal == NULL ) return SIGNAL_ERROR;
 	uint64_t ret;
+	const int signalFd = ( (int)(intptr_t)signal ) - 1;
 	if ( read( signalFd, &ret, sizeof ret ) != sizeof ret ) {
 		if ( errno == EAGAIN ) return 0;
 		return SIGNAL_ERROR;
@@ -45,8 +60,15 @@ int signal_clear(int signalFd)
 	return (int)ret;
 }
 
-void signal_close(int signalFd)
+void signal_close(const dnbd3_signal_t* const signal)
 {
+	const int signalFd = ( (int)(intptr_t)signal ) - 1;
 	close( signalFd );
 }
 
+int signal_getWaitFd(const dnbd3_signal_t* const signal)
+{
+	const int signalFd = ( (int)(intptr_t)signal ) - 1;
+	return signalFd;
+}
+
diff --git a/src/shared/signal.h b/src/shared/signal.h
index 6fd2765..3eea6fb 100644
--- a/src/shared/signal.h
+++ b/src/shared/signal.h
@@ -5,23 +5,25 @@
 #define SIGNAL_TIMEOUT (-2)
 #define SIGNAL_ERROR (-1)
 
+typedef struct _dnbd3_signal dnbd3_signal_t;
+
 /**
- * Create a new signal fd (eventfd), nonblocking.
- * @return >= 0 on success, which is the fd; < 0 on error
+ * Create a new signal, nonblocking.
+ * @return NULL on error, pointer to dnbd3_signal_t on success.
  */
-int signal_new();
+dnbd3_signal_t* signal_new();
 
 /**
- * Create a new signal fd (eventfd), blocking.
- * @return >= 0 on success, which is the fd; < 0 on error
+ * Create a new signal, blocking.
+ * @return NULL on error, pointer to dnbd3_signal_t on success.
  */
-int signal_newBlocking();
+dnbd3_signal_t* signal_newBlocking();
 
 /**
  * Trigger the given signal, so a wait or clear call will succeed.
  * @return SIGNAL_OK on success, SIGNAL_ERROR on error
  */
-int signal_call(int signalFd);
+int signal_call(const dnbd3_signal_t* const signal);
 
 /**
  * Wait for given signal, with an optional timeout.
@@ -31,18 +33,25 @@ int signal_call(int signalFd);
  *    SIGNAL_TIMEOUT if the timeout was reached,
  *    SIGNAL_ERROR if some error occured
  */
-int signal_wait(int signalFd, int timeoutMs);
+int signal_wait(const dnbd3_signal_t* const signal, int timeoutMs);
 
 /**
- * Clears any pending signals on this signal fd.
+ * Clears any pending signals on this signal.
  * @return number of signals that were pending,
  *    SIGNAL_ERROR if some error occured
  */
-int signal_clear(int signalFd);
+int signal_clear(const dnbd3_signal_t* const signal);
 
 /**
  * Close the given signal.
  */
-void signal_close(int signalFd);
+void signal_close(const dnbd3_signal_t* const signal);
+
+/**
+ * Get a file descriptor for the given signal that can be
+ * waited on using poll or similar.
+ * @return -1 if the signal is invalid
+ */
+int signal_getWaitFd(const dnbd3_signal_t* const signal);
 
 #endif