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__.
Backports commit 1e9b65bb1bad51735cab6c861c29b592dccabf0e from qemu
