Re: [Qemu-devel] [PATCH v2 7/7] error: On abort, report where the error was created

[Laszlo Ersek <lersek@redhat.com>]

On 07/23/15 16:47, Eric Blake wrote:
> On 07/23/2015 08:01 AM, Markus Armbruster wrote:
>> 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 /work/armbru/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>
>> ---
>>  include/qapi/error.h        | 43 +++++++++++++++++++++++++++--------
>>  qga/vss-win32.c             |  2 +-
>>  qga/vss-win32/requester.cpp |  5 +++--
>>  qga/vss-win32/requester.h   |  6 +++--
>>  util/error.c                | 55 ++++++++++++++++++++++++++++++++-------------
>>  5 files changed, 81 insertions(+), 30 deletions(-)
>>
> 
>> +++ 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__))
> 
> Indentation looks odd here, but not fatal.
> 
>> -void error_setg_errno(Error **errp, int os_errno, const char *fmt, ...)
>> +void error_setg_errno_internal(Error **errp,
>> +                               const char *src, int line, const char *func,
>> +                              int os_errno, const char *fmt, ...)
> 
> Indentation off again.
> 
> Those are minor, and could be fixed by maintainer.
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 

I'm going to freeload in the wake of Eric's review, and just say "thank
you" for including __func__.

Acked-by: Laszlo Ersek <lersek@redhat.com>