Messages in this thread | | | Date | Sun, 8 Mar 2015 12:31:25 +0100 | From | Jean Delvare <> | Subject | Re: [dmidecode] [Patch v3] firmware: dmi-sysfs: add SMBIOS entry point area raw attribute |
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Hi Ivan,
On Sat, 07 Mar 2015 22:53:32 +0200, Ivan.khoronzhuk wrote: > On 03/05/2015 09:46 AM, Jean Delvare wrote: > > It's not just two tables (I don't expect a lot of BIOSes to provide two > > tables in practice, and they would have essentially the same format > > anyway) but more importantly two entry points. The _SM3_ entry point is > > brand new and most applications (including dmidecode) don't support it > > yet. It doesn't matter if the kernel itself can parse it, as it passes > > the raw entry point to applications anyway. > > > > It happens that we are introducing this new sysfs raw interface at the > > same time _SM3_ is being introduced, so we do not have to care about > > backwards compatibility. Both the kernel and dmidecode will need to be > > updated to support the new interface, so we can keep things simple and > > let the kernel expose only the best entry point. > > > > If the sysfs raw interface was already present at the time _SM3_ > > support was being added, then we would have had to present both entry > > points for backwards compatibility. And if some _SM4_ entry point is > > ever added in the future with a new format, we will have to export it > > as a new sysfs attribute so as to not break compatibility. > > > > As a summary, I agree that a single entry point file is OK for now, but > > only because we are lucky that the timing is right. > > Despite of timing is right. > > The specification doesn't oblige firmware to provide two entry points. > An implementation may provide either the 32-bit entry point or the 64-bit > entry point, or both. For compatibility with existing SMBIOS parsers, an > implementation should provide the 32-bit entry point, but it's not required.
I expect most implementations will do, as it's trivial to implement.
> Another case if specification requires to provide two entry points. Then > you can > be sure in backward compatibility. But at least for now you can't. > > It's obvious, if kernel found two entry points then it can create two > sysfs attributes. > But, what kernel should do in case if only one new entry point is present. > Generate entry point of old version..., sorry but it's bad idea. At > least because > where guarantee that we have enough information for this. Only field we > can bring > thought entry point versions is magic string _SM*_, and based on it, if util > don't support new version it can warn. It's used for differ versions and > there is nothing we can do more.
I agree that the kernel should not fake an entry point which does not exist (I'm not sure if you misunderstood me but I never suggested that.)
-- Jean Delvare SUSE L3 Support
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