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

[Eric Blake]

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 <address@hidden>
> ---
>  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 <address@hidden>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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