[pending] Add concept of "pending operations"

iPXE is fundamentally asynchronous in operation: some operations
continue in the background even after the foreground has continued to
a new task.  For example, the closing FIN/ACK exchanges of a TCP
connection will take place in the background after an HTTP download
has completed.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/pending.c

@@ -0,0 +1,79 @@
+/*
+ * Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <errno.h>
+#include <ipxe/process.h>
+#include <ipxe/timer.h>
+#include <ipxe/pending.h>
+
+/** @file
+ *
+ * Pending operations
+ *
+ */
+
+/** Total count of pending operations */
+static int pending_total;
+
+/**
+ * Mark an operation as pending
+ *
+ * @v pending		Pending operation
+ */
+void pending_get ( struct pending_operation *pending ) {
+
+	pending->count++;
+	pending_total++;
+	DBGC ( pending, "PENDING %p incremented to %d (total %d)\n",
+	       pending, pending->count, pending_total );
+}
+
+/**
+ * Mark an operation as no longer pending
+ *
+ * @v pending		Pending operation
+ */
+void pending_put ( struct pending_operation *pending ) {
+
+	if ( pending->count ) {
+		pending_total--;
+		pending->count--;
+		DBGC ( pending, "PENDING %p decremented to %d (total %d)\n",
+		       pending, pending->count, pending_total );
+	}
+}
+
+/**
+ * Wait for pending operations to complete
+ *
+ * @v timeout		Timeout period, in ticks (0=indefinite)
+ * @ret rc		Return status code
+ */
+int pending_wait ( unsigned long timeout ) {
+	unsigned long start = currticks();
+
+	do {
+		if ( pending_total == 0 )
+			return 0;
+		step();
+	} while ( ( timeout == 0 ) || ( ( currticks() - start ) < timeout ) );
+
+	return -ETIMEDOUT;
+}

src/include/ipxe/errfile.h

@@ -62,6 +62,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define ERRFILE_parseopt	       ( ERRFILE_CORE | 0x00160000 )
 #define ERRFILE_test		       ( ERRFILE_CORE | 0x00170000 )
 #define ERRFILE_xferbuf		       ( ERRFILE_CORE | 0x00180000 )
+#define ERRFILE_pending		       ( ERRFILE_CORE | 0x00190000 )
 
 #define ERRFILE_eisa		     ( ERRFILE_DRIVER | 0x00000000 )
 #define ERRFILE_isa		     ( ERRFILE_DRIVER | 0x00010000 )

src/include/ipxe/pending.h

@@ -0,0 +1,34 @@
+#ifndef _IPXE_PENDING_H
+#define _IPXE_PENDING_H
+
+/** @file
+ *
+ * Pending operations
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <ipxe/list.h>
+
+/** A pending operation */
+struct pending_operation {
+	/** Pending count */
+	unsigned int count;
+};
+
+/**
+ * Check if an operation is pending
+ *
+ * @v pending		Pending operation
+ * @v is_pending	Operation is pending
+ */
+static inline int is_pending ( struct pending_operation *pending ) {
+	return ( pending->count != 0 );
+}
+
+extern void pending_get ( struct pending_operation *pending );
+extern void pending_put ( struct pending_operation *pending );
+extern int pending_wait ( unsigned long timeout );
+
+#endif /* _IPXE_PENDING_H */