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qga/vss-win32: Document the DLL requires non-null errp

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requester.cpp uses this pattern to receive an error and pass it on to
the caller (err_is_set() macro peeled off for clarity):

    ... code that may set errset->errp ...
    if (errset->errp && *errset->errp) {
        ... handle error ...
    }

This breaks when errset->errp is null.  As far as I can tell, it
currently isn't, so this is merely fragile, not actually broken.

The robust way to do this is to receive the error in a local variable,
then propagate it up, like this:

    Error *err = NULL;

    ... code that may set err ...
    if (err)
        ... handle error ...
        error_propagate(errset->errp, err);
    }

See also commit 5e54769, 0f230bf, a903f40.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Markus Armbruster 2015-06-20 09:33:56 +02:00
parent e7cf59e847
commit 08e6464035
3 changed files with 4 additions and 2 deletions
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3
qga/vss-win32/requester.cpp
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@ -25,8 +25,9 @@
#define err_set(e, err, fmt, ...) \
((e)->error_setg_win32((e)->errp, 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 */
/* Handle to VSSAPI.DLL */
static HMODULE hLib;