Re: [Xen-devel] [PATCH] libxl: fix an error path that uses uninitialised rc in libxl_set_memory_target

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.06.16 at 15:59, <wei.liu2@xxxxxxxxxx> wrote:
> On Wed, Jun 22, 2016 at 07:53:56AM -0600, Jan Beulich wrote:
>> >>> On 22.06.16 at 15:47, <wei.liu2@xxxxxxxxxx> wrote:
>> > On Wed, Jun 22, 2016 at 06:58:28AM -0600, Jan Beulich wrote:
>> >> >>> On 12.06.16 at 16:09, <wei.liu2@xxxxxxxxxx> wrote:
>> >> > --- a/tools/libxl/libxl.c
>> >> > +++ b/tools/libxl/libxl.c
>> >> > @@ -4927,10 +4927,12 @@ retry_transaction:
>> >> >  
>> >> >      target = libxl__xs_read(gc, t, GCSPRINTF("%s/memory/target", 
> dompath));
>> >> >      if (!target && !domid) {
>> >> > -        if (!xs_transaction_end(ctx->xsh, t, 1))
>> >> > +        if (!xs_transaction_end(ctx->xsh, t, 1)) {
>> >> > +            rc = ERROR_FAIL;
>> >> 
>> >> I'm sorry for noticing this only now - is ERROR_FAIL the right thing
>> >> to use here, considering how things worked before the change that
>> >> introduced the issue getting fixed here? I had intentionally decided
>> >> to use ERROR_INVAL in the patch variant I did submit (as at that
>> >> time I wasn't yet aware of the other fix floating around already).
>> >> 
>> > 
>> > When I wrote this patch, I thought the return value should be tied to
>> > xs_transaction_end.
>> 
>> xs_transaction_end() returning zero means success afaict.
>> 
> 
> /* End a transaction.
>  * If abandon is true, transaction is discarded instead of committed.
>  * Returns false on failure: if errno == EAGAIN, you have to restart
>  * transaction.
>  */
> bool xs_transaction_end(struct xs_handle *h, xs_transaction_t t,
>                         bool abort);
> 
> I think you misread.

Indeed, I got mislead by "goto out_no_transaction". Yet that
doesn't change the discussion of the error - originally this didn't
return -1 here, but +1 (i.e. reflecting the surrounding if(), not
the inner one).

Jan


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