Commit 08e64640 authored by Markus Armbruster's avatar Markus Armbruster
Browse files

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



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 5e54769c, 0f230bf7, a903f40c.

Signed-off-by: default avatarMarkus Armbruster <armbru@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
parent e7cf59e8

qga/vss-win32.c

+1 −0
Original line number Diff line number Diff line
@@ -154,6 +154,7 @@ void qga_vss_fsfreeze(int *nr_volume, Error **errp, bool freeze) 
        .errp = errp,

    };



    g_assert(errp);             /* requester.cpp requires it */

    func = (QGAVSSRequesterFunc)GetProcAddress(provider_lib, func_name);

    if (!func) {

        error_setg_win32(errp, GetLastError(), "failed to load %s from %s",

qga/vss-win32/requester.cpp

+2 −1
Original line number Diff line number Diff line
@@ -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;

qga/vss-win32/requester.h

+1 −1
Original line number Diff line number Diff line
@@ -27,7 +27,7 @@ typedef void (*ErrorSetFunc)(struct Error **errp, int win32_err, 
                             const char *fmt, ...) GCC_FMT_ATTR(3, 4);

typedef struct ErrorSet {

    ErrorSetFunc error_setg_win32;

    struct Error **errp;

    struct Error **errp;        /* restriction: must not be null */

} ErrorSet;



STDAPI requester_init(void);