Introduce the new error framework

New error-handling framework that allows for exception-like error
propagation.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

error.h

@@ -0,0 +1,70 @@
+/*
+ * QEMU Error Objects
+ *
+ * Copyright IBM, Corp. 2011
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.  See
+ * the COPYING.LIB file in the top-level directory.
+ */
+#ifndef ERROR_H
+#define ERROR_H
+
+#include <stdbool.h>
+
+/**
+ * A class representing internal errors within QEMU.  An error has a string
+ * typename and optionally a set of named string parameters.
+ */
+typedef struct Error Error;
+
+/**
+ * Set an indirect pointer to an error given a printf-style format parameter.
+ * Currently, qerror.h defines these error formats.  This function is not
+ * meant to be used outside of QEMU.
+ */
+void error_set(Error **err, const char *fmt, ...)
+    __attribute__((format(printf, 2, 3)));
+
+/**
+ * Returns true if an indirect pointer to an error is pointing to a valid
+ * error object.
+ */
+bool error_is_set(Error **err);
+
+/**
+ * Get a human readable representation of an error object.
+ */
+const char *error_get_pretty(Error *err);
+
+/**
+ * Get an individual named error field.
+ */
+const char *error_get_field(Error *err, const char *field);
+
+/**
+ * Get an individual named error field.
+ */
+void error_set_field(Error *err, const char *field, const char *value);
+
+/**
+ * Propagate an error to an indirect pointer to an error.  This function will
+ * always transfer ownership of the error reference and handles the case where
+ * dst_err is NULL correctly.
+ */
+void error_propagate(Error **dst_err, Error *local_err);
+
+/**
+ * Free an error object.
+ */
+void error_free(Error *err);
+
+/**
+ * Determine if an error is of a speific type (based on the qerror format).
+ * Non-QEMU users should get the `class' field to identify the error type.
+ */
+bool error_is_type(Error *err, const char *fmt);
+
+#endif