On Sun, 2018-06-10 at 21:12 +1200, Michael Schmitz wrote: > Hi Geert, Top posting, sorry ...
We are painting that bike shed with way too many coats.. We can keep the existing definitions, stick a comment on them stating "obsolete" and use new number if/when needed. Ben. > Am 10.06.2018 um 20:29 schrieb Geert Uytterhoeven: > > Hi Finn, > > > > On Sat, Jun 9, 2018 at 2:20 PM Finn Thain <fth...@telegraphics.com.au> > > wrote: > > > > > > Is this enum used by any user space code? If so, perhaps rather > > > > > > leave the PMU_68K_V1 in there to avoid upsetting that? > > > > > > > > > > It also changes the value of PMU_68K_V2, which is an ABI break. > > > > > > > > Yes, that's what I worry about - but do we know of any users of that > > > > particular interface? > > > > > > There is no ABI issue AFAIK. The value of pmu_kind is visible to userland > > > only on powerpc. /dev/pmu and /proc/pmu/* do not exist on m68k. This patch > > > series will make these UAPIs available on m68k, and for that reason I've > > > chosen the value PMU_UNKNOWN for pmu_kind. > > > > While /dev/pmu and /proc/pmu/* may not exist on m68k, definitions in > > include/uapi/linux/pmu.h are part of the ABI, and cannot be changed or > > removed, > > unless we are 100% sure there are no users. > > > > If I would write a program interfacing with /dev/pmu and /proc/pmu/*, and > > needing to check the PMU type, it would have a switch() statement with > > all existing values defined in <linux/pmu.h>. So that would become broken > > by your change. > > > > Hence the enum is append-only. > > The PMU type from pmu.h was never exposed to user space on m68k via > /proc/pmu/*, and /dev/pmu is used for ioctls to the PMU driver on > powerpc only (the 68k PMU driver doesn't have ioctl support). No way > that I can see for user space to make use of the PMU type definition > from pmu.h, so I suppose we can be sure there are no users. > > The m68k PMU types cannot be said to be exposed on powerpc either (which > has ioctl support to interrogate the PMU type), as these only return > values up to PMU_KEYLARGO_BASED. > > Applications like pbbuttonsd or pmud don't use the kernel PMU type at > all, but go straight to the PMU via the ADB bus to interrogate the > hardware type, so won't be affected either. > > Is there any other way besides procfs and ioctl for user space to > interrogate the PMU type that I'm missing here? > > (I understand that breaking the ABI should not be done as a rule, but > this may be a case where we can successfully argue the definitions were > never in use, so the rules may be bent a little).
