Re: [Qemu-devel] [for-4.0 PATCH v3 3/9] qapi: Define PCIe link speed and width properties

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 05 Dec 2018 15:16:27 +0100
Markus Armbruster <armbru@redhat.com> wrote:

> Auger Eric <eric.auger@redhat.com> writes:
> 
> > Hi Alex,
> >
> > On 12/4/18 5:26 PM, Alex Williamson wrote:  
> >> Create properties to be able to define speeds and widths for PCIe
> >> links.  The only tricky bit here is that our get and set callbacks
> >> translate from the fixed QAPI automagic enums to those we define
> >> in PCI code to represent the actual register segment value.
> >> 
> >> Cc: Eric Blake <eblake@redhat.com>
> >> Cc: Markus Armbruster <armbru@redhat.com>
> >> Tested-by: Geoffrey McRae <geoff@hostfission.com>
> >> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> >> ---
> >>  hw/core/qdev-properties.c    |  178 ++++++++++++++++++++++++++++++++++++++++++
> >>  include/hw/qdev-properties.h |    8 ++
> >>  qapi/common.json             |   42 ++++++++++
> >>  3 files changed, 228 insertions(+)
> >> 
> >> diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
> >> index 35072dec1ecf..f5ca5b821a79 100644
> >> --- a/hw/core/qdev-properties.c
> >> +++ b/hw/core/qdev-properties.c
> >> @@ -1327,3 +1327,181 @@ const PropertyInfo qdev_prop_off_auto_pcibar = {
> >>      .set = set_enum,
> >>      .set_default_value = set_default_value_enum,
> >>  };
> >> +
> >> +/* --- PCIELinkSpeed 2_5/5/8/16 -- */
> >> +
> >> +static void get_prop_pcielinkspeed(Object *obj, Visitor *v, const char *name,
> >> +                                   void *opaque, Error **errp)
> >> +{
> >> +    DeviceState *dev = DEVICE(obj);
> >> +    Property *prop = opaque;
> >> +    PCIExpLinkSpeed *p = qdev_get_prop_ptr(dev, prop);
> >> +    PCIELinkSpeed speed;
> >> +
> >> +    switch (*p) {
> >> +    case QEMU_PCI_EXP_LNK_2_5GT:
> >> +        speed = PCIE_LINK_SPEED_2_5;
> >> +        break;
> >> +    case QEMU_PCI_EXP_LNK_5GT:
> >> +        speed = PCIE_LINK_SPEED_5;
> >> +        break;
> >> +    case QEMU_PCI_EXP_LNK_8GT:
> >> +        speed = PCIE_LINK_SPEED_8;
> >> +        break;
> >> +    case QEMU_PCI_EXP_LNK_16GT:
> >> +        speed = PCIE_LINK_SPEED_16;
> >> +        break;
> >> +    default:
> >> +        /* Unreachable */
> >> +        abort();  
> > nit: g_assert_not_reached() here and below.  
> 
> In my opinion, g_assert_not_reached() & friends are an overly ornate
> reinvention of an old and perfectly adequate wheel.
> 
> A long time ago for reasons since forgotten, the maintainers in charge
> back then demanded abort() instead of assert(0).  Either is fine with
> me.
> 
> I tolerate g_assert_not_reached() in files that already use g_assert().
> This one doesn't.
> 
> In any case, I'd drop the comment.

I added the comment because as a casual QAPI contributor it's otherwise
not obvious that bogus user input can't reach that case.  Comments are
free.
 
> Note that I'm not this file's maintainer.

get_maintainer.pl says there is no maintainer here and references:

"Michael S. Tsirkin" <mst@redhat.com> (commit_signer:3/4=75%)
"Marc-André Lureau" <marcandre.lureau@redhat.com> (commit_signer:2/4=50%)
Markus Armbruster <armbru@redhat.com> (commit_signer:1/4=25%)
"Philippe Mathieu-Daudé" <f4bug@amsat.org> (commit_signer:1/4=25%)
Paolo Bonzini <pbonzini@redhat.com> (commit_signer:1/4=25%)

CC'ing those folks.  Unless anyone expresses a strong opinion or trend
towards using g_assert_not_reached(), I'll stick with Markus' style to
only use it in files where g_assert() is already present... or at least
claim that's why I didn't use it ;)  Thanks,

Alex