Messages in this thread |  | | Date | Wed, 4 Dec 2013 10:43:16 +0100 | From | Roger Pau Monné <> | Subject | Re: [Xen-devel] [PATCH RFC] xen-block: correctly define structures in public headers |
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On 04/12/13 10:28, Ian Campbell wrote: > On Tue, 2013-12-03 at 15:11 -0500, Konrad Rzeszutek Wilk wrote: >>>> If Konrad and Boris agree that breaking the kernel's ABI in this way is >>>> acceptable in this specific case, I'll defer to them. >>> >>> My opinion as Xen on ARM hypervisor maintainer is that this is the right >>> thing to do in this case. >> >> Heh. If somebody can guarantee me that (by testing the right variants and >> mentioning this in the git commit) that this does not break x86, then >> I am fine. >> >> And by 'break x86' I mean that this combination works: >> 32-bit domU on 64-bit dom0 >> 64-bit domU on 32-bit dom0 >> >> And perhaps also the obvious: >> 64-bit domU on 64-bit dom0 >> 32-bit domU on 32-bit dom0 > > One way to test this is with gdb on a vmlinux for each arch with > CONFIG_DEBUG_INFO=y. For each MEMBER of each interesting STRUCT: > (gdb) print &((struct STRUCT *)0)->MEMBER > (this is effectively an open coded offsetof) > > This could probably even be semi automated by producing a script to feed > to gdb which run through all of the options and diffing the result. > > If I could have the moon on a stick I would have a tool such as this > running against the canonical Xen headers, to catch breakage as it is > introduced upstream and a tool which could run against an arbitrary ELF > binary to validate it against the upstream results. > tools/include/xen-foreign/mkchecker.py goes some way towards that but > isn't really extensible to the extent we would need/want. > > While I'm asking for unicorns a gcc __attribute__((warn_on_holes)) which > could be applied to a struct to enforce the need for explicit padding > would probably be incredibly useful for this of thing.
Right now I would be happy to add something like:
#if !defined(CONFIG_X86_32) && !defined(CONFIG_X86_64) && !defined(CONFIG_ARM... #error This architecture is not supported by the Xen PV block ABI #endif
To the Linux copy of blkif.h
>> Since the xen-blkback has its own version of the structs there is no >> need to change change newer and older version of it. > > Someone should check that these are producing the right interface on ARM > though!
AFAICT blkback on ARM is not using the structures defined in blkback/common.h, since the protocol is "native", it's using the same structures defined in the public header (just as blkfront). There's no translation needed and blkback just does a memcpy from the ring to the native struct.
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