[Qemu-devel] [PATCH 03/11] add a generic Error object

[Anthony Liguori <aliguori@us.ibm.com>]

The Error class is similar to QError (now deprecated) except that it supports
propagation.  This allows for higher quality error handling.  It's losely
modeled after glib style GErrors.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

diff --git a/Makefile.objs b/Makefile.objs
index 0ba02c7..da31530 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -15,6 +15,7 @@ oslib-obj-$(CONFIG_POSIX) += oslib-posix.o
 
 block-obj-y = cutils.o cache-utils.o qemu-malloc.o qemu-option.o module.o
 block-obj-y += nbd.o block.o aio.o aes.o qemu-config.o
+block-obj-y += error.o
 block-obj-$(CONFIG_POSIX) += posix-aio-compat.o
 block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
 
diff --git a/error.c b/error.c
new file mode 100644
index 0000000..5d84106
--- /dev/null
+++ b/error.c
@@ -0,0 +1,122 @@
+/*
+ * 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.
+ */
+#include "error.h"
+#include "error_int.h"
+#include "qemu-objects.h"
+#include "qerror.h"
+#include <assert.h>
+
+struct Error
+{
+    QDict *obj;
+    const char *fmt;
+    char *msg;
+};
+
+void error_set(Error **errp, const char *fmt, ...)
+{
+    Error *err;
+    va_list ap;
+
+    if (errp == NULL) {
+        return;
+    }
+
+    err = qemu_mallocz(sizeof(*err));
+
+    va_start(ap, fmt);
+    err->obj = qobject_to_qdict(qobject_from_jsonv(fmt, &ap));
+    va_end(ap);
+    err->fmt = fmt;
+
+    *errp = err;
+}
+
+bool error_is_set(Error **errp)
+{
+    return (errp && *errp);
+}
+
+const char *error_get_pretty(Error *err)
+{
+    if (err->msg == NULL) {
+        QString *str;
+        str = qerror_format(err->fmt, err->obj);
+        err->msg = qemu_strdup(qstring_get_str(str));
+    }
+
+    return err->msg;
+}
+
+const char *error_get_field(Error *err, const char *field)
+{
+    if (strcmp(field, "class") == 0) {
+        return qdict_get_str(err->obj, field);
+    } else {
+        QDict *dict = qdict_get_qdict(err->obj, "data");
+        return qdict_get_str(dict, field);
+    }
+}
+
+void error_free(Error *err)
+{
+    QDECREF(err->obj);
+    qemu_free(err->msg);
+    qemu_free(err);
+}
+
+bool error_is_type(Error *err, const char *fmt)
+{
+    char *ptr;
+    char *end;
+    char classname[1024];
+
+    ptr = strstr(fmt, "'class': '");
+    assert(ptr != NULL);
+    ptr += strlen("'class': '");
+
+    end = strchr(ptr, '\'');
+    assert(end != NULL);
+    
+    memcpy(classname, ptr, (end - ptr));
+    classname[(end - ptr)] = 0;
+
+    return strcmp(classname, error_get_field(err, "class")) == 0;
+}
+
+void error_propagate(Error **dst_err, Error *local_err)
+{
+    if (dst_err) {
+        *dst_err = local_err;
+    } else if (local_err) {
+        error_free(local_err);
+    }
+}
+
+QObject *error_get_qobject(Error *err)
+{
+    QINCREF(err->obj);
+    return QOBJECT(err->obj);
+}
+
+void error_set_qobject(Error **errp, QObject *obj)
+{
+    Error *err;
+    if (errp == NULL) {
+        return;
+    }
+    err = qemu_mallocz(sizeof(*err));
+    err->obj = qobject_to_qdict(obj);
+    qobject_incref(obj);
+
+    *errp = err;
+}
diff --git a/error.h b/error.h
new file mode 100644
index 0000000..317d487
--- /dev/null
+++ b/error.h
@@ -0,0 +1,65 @@
+/*
+ * 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);
+
+/**
+ * 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
diff --git a/error_int.h b/error_int.h
new file mode 100644
index 0000000..eaba65e
--- /dev/null
+++ b/error_int.h
@@ -0,0 +1,27 @@
+/*
+ * 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 QEMU_ERROR_INT_H
+#define QEMU_ERROR_INT_H
+
+#include "qemu-common.h"
+#include "qobject.h"
+#include "error.h"
+
+/**
+ * Internal QEMU functions for working with Error.
+ *
+ * These are used to convert QErrors to Errors
+ */
+QObject *error_get_qobject(Error *err);
+void error_set_qobject(Error **errp, QObject *obj);
+  
+#endif
-- 
1.7.0.4