error: On abort, report where the error was created

This is particularly useful when we abort in error_propagate(),
because there the stack backtrace doesn't lead to where the error was
created.  Looks like this:

    Unexpected error in parse_block_error_action() at .../qemu/blockdev.c:322:
    qemu-system-x86_64: -drive if=none,werror=foo: 'foo' invalid write error action
    Aborted (core dumped)

Note: to get this example output, I monkey-patched drive_new() to pass
&error_abort to blockdev_init().

To keep the error handling boiler plate from growing even more, all
error_setFOO() become macros expanding into error_setFOO_internal()
with additional __FILE__, __LINE__, __func__ arguments.  Not exactly
pretty, but it works.

The macro trickery breaks down when you take the address of an
error_setFOO().  Fortunately, we do that in just one place: qemu-ga's
Windows VSS provider and requester DLL wants to call
error_setg_win32() through a function pointer "to avoid linking glib
to the DLL".  Use error_setg_win32_internal() there.  The use of the
function pointer is already wrapped in a macro, so the churn isn't
bad.

Code size increases by some 35KiB for me (0.7%).  Tolerable.  Could be
less if we passed relative rather than absolute source file names to
the compiler, or forwent reporting __func__.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>

2 files changed, 7 insertions, 4 deletions

diff --git a/qga/vss-win32/requester.cpp b/qga/vss-win32/requester.cpp
index aae0d5f..9b3e310 100644
--- a/qga/vss-win32/requester.cpp
+++ b/qga/vss-win32/requester.cpp
@@ -23,8 +23,9 @@
 /* Call QueryStatus every 10 ms while waiting for frozen event */
 #define VSS_TIMEOUT_EVENT_MSEC 10
 
-#define err_set(e, err, fmt, ...) \
-    ((e)->error_setg_win32((e)->errp, err, fmt, ## __VA_ARGS__))
+#define err_set(e, err, fmt, ...)                                       \
+    ((e)->error_setg_win32((e)->errp, __FILE__, __LINE__, __func__,     \
+                           err, fmt, ## __VA_ARGS__))
 /* Bad idea, works only when (e)->errp != NULL: */
 #define err_is_set(e) ((e)->errp && *(e)->errp)
 /* To lift this restriction, error_propagate(), like we do in QEMU code */
diff --git a/qga/vss-win32/requester.h b/qga/vss-win32/requester.h
index 34be5c1..c3093cf 100644
--- a/qga/vss-win32/requester.h
+++ b/qga/vss-win32/requester.h
@@ -23,8 +23,10 @@ extern "C" {
 struct Error;
 
 /* Callback to set Error; used to avoid linking glib to the DLL */
-typedef void (*ErrorSetFunc)(struct Error **errp, int win32_err,
-                             const char *fmt, ...) GCC_FMT_ATTR(3, 4);
+typedef void (*ErrorSetFunc)(struct Error **errp,
+                             const char *src, int line, const char *func,
+                             int win32_err, const char *fmt, ...)
+    GCC_FMT_ATTR(6, 7);
 typedef struct ErrorSet {
     ErrorSetFunc error_setg_win32;
     struct Error **errp;        /* restriction: must not be null */