Re: [Qemu-devel] [PATCH v3] Add param Error ** for msi_init()

[Marcel Apfelbaum]

On 03/30/2016 07:10 AM, Cao jin wrote:
> Hi Marcel,
>     Thanks for your quick review for this big fat patch:)
>     please see my comments inline.
>
> On 03/30/2016 04:56 AM, Marcel Apfelbaum wrote:
> > On 03/28/2016 01:44 PM, Cao jin wrote:
>
> > > -#define VMXNET3_USE_64BIT         (true)
> > > -#define VMXNET3_PER_VECTOR_MASK   (false)
> > > -
> > > -static bool
> > > -vmxnet3_init_msi(VMXNET3State *s)
> > > -{
> > > -    PCIDevice *d = PCI_DEVICE(s);
> > > -    int res;
> > > -
> > > -    res = msi_init(d, VMXNET3_MSI_OFFSET(s), VMXNET3_MAX_NMSIX_INTRS,
> > > -                   VMXNET3_USE_64BIT, VMXNET3_PER_VECTOR_MASK);
> > > -    if (0 > res) {
> > > -        VMW_WRPRN("Failed to initialize MSI, error %d", res);
> > > -        s->msi_used = false;
> > > -    } else {
> > > -        s->msi_used = true;
> > > -    }
> > > -
> > > -    return s->msi_used;
> > > -}
> > > -
> > >   static void
> > >   vmxnet3_cleanup_msi(VMXNET3State *s)
> > >   {
> > > @@ -2271,6 +2250,10 @@ static uint8_t
> > > *vmxnet3_device_serial_num(VMXNET3State *s)
> > >       return dsnp;
> > >   }
> > >
> > > +
> > > +#define VMXNET3_USE_64BIT         (true)
> > > +#define VMXNET3_PER_VECTOR_MASK   (false)
> > > +
> > >   static void vmxnet3_pci_realize(PCIDevice *pci_dev, Error **errp)
> > >   {
> > >       DeviceState *dev = DEVICE(pci_dev);
> > > @@ -2278,6 +2261,16 @@ static void vmxnet3_pci_realize(PCIDevice
> > > *pci_dev, Error **errp)
> > >
> > >       VMW_CBPRN("Starting init...");
> > >
> > > +    msi_init(pci_dev, VMXNET3_MSI_OFFSET(s), VMXNET3_MAX_NMSIX_INTRS,
> > > +             VMXNET3_USE_64BIT, VMXNET3_PER_VECTOR_MASK, errp);
> > > +    if (*errp) {
> > > +        error_report_err(*errp);
> > > +        *errp = NULL;
> >
> > You suppress prev debug message: VMW_WRPRN("Failed to initialize MSI,
> > error %d", res),
> > but you replace with one of yourself. If the vmxnet maintainers have
> > nothing against,
> > I suppose is OK.
> >
> > Then, you don't propagate the error because you don't want realize
> > to fail, so you report it and NULL it. I suppose we should have
> > a "warning only" error type so the reporting party can decide to issue a
> > warning
> > or to fail, but is out of the scope of this patch, of course.

Hi,

> Yes, I should add more hint message. I don`t quite understand about:
>
> /have a "warning only" error type so the reporting party can decide to issue a  
> warning or to fail/
>
> Do you mean still using VMW_WRPRN or using error_append_hint? It seems 
> VMW_WRPRN should only work in debug time? and if user should see this error 
> message, should use error_report_err ?

No, it is not related to VMW_WRPRN. On this subject, those are debugging 
warnings
and we should keep them the same as before.

About the "warning only" error type: if an error is returned, the caller
assumes that the initialization failed and it will return with failure. That 
means
that you cannot return a non-null error if you want the process to finish OK.

This is why you had to:
   -  report the error (even if this function should not be a reporter because 
it receives an Error parameter)
   -  empty the error: so why use error at all, right?

My point is if the caller had a way to check what kind of error this is
and act accordingly, it would be nicer. But again, this is out of the scope of 
this patch, only some thoughts.

> > > -    if (!vmxnet3_init_msi(s)) {
> > > -        VMW_WRPRN("Failed to initialize MSI, configuration is
> > > inconsistent.");
> >
> > Here again you remove an existent debug warning, maybe you should keep it.
> >
> > > -    }
> > > -
> > >       vmxnet3_net_init(s);
>
> > > diff --git a/hw/pci-bridge/pci_bridge_dev.c
> > > b/hw/pci-bridge/pci_bridge_dev.c
> > > index 862a236..07c7bf8 100644
> > > --- a/hw/pci-bridge/pci_bridge_dev.c
> > > +++ b/hw/pci-bridge/pci_bridge_dev.c
> > > @@ -52,6 +52,7 @@ static int pci_bridge_dev_initfn(PCIDevice *dev)
> > >       PCIBridge *br = PCI_BRIDGE(dev);
> > >       PCIBridgeDev *bridge_dev = PCI_BRIDGE_DEV(dev);
> > >       int err;
> > > +    Error *local_err = NULL;
> >
> > You use both local_err and err for local error names. It doesn't really
> > matter
> > the name, but please be consistent. I personally like local_error but is
> > up to you, of course.
>
> Yes, I prefer consistent way, but here, you see there is a "int err", so I 
> thought two different variants using same name maybe not so good for reading code?  what 
> would you choose?(I like local_err
> at first because it is easy to understand for newbie, but when I get familiar 
> with error handling, I turn to like err, just because it is shorter:p)

Indeed is a little confusing, this is why I prefer "local_error" because it is 
used widely
and became a familiar pattern.

> > >       pci_bridge_initfn(dev, TYPE_PCI_BUS);
> > >
> > > @@ -67,17 +68,21 @@ static int pci_bridge_dev_initfn(PCIDevice *dev)
> > >           /* MSI is not applicable without SHPC */
> > >           bridge_dev->flags &= ~(1 << PCI_BRIDGE_DEV_F_MSI_REQ);
> > >       }
> > > +
> > >       err = slotid_cap_init(dev, 0, bridge_dev->chassis_nr, 0);
> > >       if (err) {
> > >           goto slotid_error;
> > >       }
> > > +
> >
> > You have several new lines (before and after this comment) that have
> > nothing
> > to do with the patch. I suggest putting them into a trivial separate patch.
>
> see what I was told before:
> http://lists.nongnu.org/archive/html/qemu-trivial/2015-10/msg00116.html
> http://lists.nongnu.org/archive/html/qemu-trivial/2015-10/msg00123.html
>
> Actually I am ok with both sides. I just stop sending coding style patch since 
> then:)

Oh, I hate when it happens to me, tho different opinions, how can you deal with 
that, right ? :)

> I don`t know, coding style & indentation patch really matters or is just a 
> personal taste thing?

Coding style and indentation *are important* IMHO.

For this case, what I would do is put the new lines and comments in a separate 
patch,\
but send it with *the same* series, not through trivial list, saying something 
like:
"fixed some code style problems while resolving the ... problem".

> > > +++ b/hw/scsi/mptsas.c
> > > @@ -1274,10 +1274,22 @@ static void mptsas_scsi_init(PCIDevice *dev,
> > > Error **errp)
> > >   {
> > >       DeviceState *d = DEVICE(dev);
> > >       MPTSASState *s = MPT_SAS(dev);
> > > +    Error *err = NULL;
> > >
> > >       dev->config[PCI_LATENCY_TIMER] = 0;
> > >       dev->config[PCI_INTERRUPT_PIN] = 0x01;
> > >
> > > +    if (s->msi_available) {
> > > +        if (msi_init(dev, 0, 1, true, false, &err) >= 0) {
> > > +            s->msi_in_use = true;
> > > +        }
> > > +        else {
> > > +            error_append_hint(&err, "MSI init fail, will use INTx
> > > instead");
> >
> > The hint should end with a new line: "\n".
> >
> > > +            error_report_err(err);
> >
> > You should not report the error if the fucntion has an **errp parameter.
>
> it will use INTx even if msi_init fail, so it should not break realize. But I 
> think user should know it if something wrong happened there，so I use a local 
> *err* to report error message, while don`t
> touch **errp. Is there any better way?

Same problem as discussed before, Markus do you have any idea how to solve this 
elegantly?
CC: Markus Armbruster <address@hidden>

Thanks,
Marcel

> >
>
> For all the other comments, will fix them in next version.