From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <54D9157D.3010905@control.lth.se> Date: Mon, 09 Feb 2015 21:15:57 +0100 From: Anders Blomdell MIME-Version: 1.0 References: <54D4D409.2020708@control.lth.se> <54D4D9B2.8090805@xenomai.org> <54D4DF0C.2080007@control.lth.se> <54D4E285.9000906@xenomai.org> <54D4E44B.4060403@control.lth.se> <20150206161215.GC27277@hermes.click-hack.org> <20150206161626.GD27277@hermes.click-hack.org> <54D8D7D5.2060000@control.lth.se> <20150209155716.GE3200@hermes.click-hack.org> <54D8DC0B.3070107@control.lth.se> <20150209162409.GF3200@hermes.click-hack.org> <54D8E83F.6020601@control.lth.se> <54D8EE0A.8040600@xenomai.org> <54D8F09A.7030802@control.lth.se> <54D913AD.8040906@xenomai.org> In-Reply-To: <54D913AD.8040906@xenomai.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] Mixing linux and alchemy (cobalt) calls List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Philippe Gerum , Gilles Chanteperdrix Cc: "Xenomai@xenomai.org" On 2015-02-09 21:08, Philippe Gerum wrote: > On 02/09/2015 06:38 PM, Anders Blomdell wrote: >> On 2015-02-09 18:27, Philippe Gerum wrote: >>> On 02/09/2015 06:02 PM, Anders Blomdell wrote: >>>> On 2015-02-09 17:24, Gilles Chanteperdrix wrote: >>>>> On Mon, Feb 09, 2015 at 05:10:51PM +0100, Anders Blomdell wrote: >>>>>> On 2015-02-09 16:57, Gilles Chanteperdrix wrote: >>>>>>> On Mon, Feb 09, 2015 at 04:52:53PM +0100, Anders Blomdell wrote: >>>>>>>> On 2015-02-06 17:16, Gilles Chanteperdrix wrote: >>>>>>>>> On Fri, Feb 06, 2015 at 05:12:15PM +0100, Gilles Chanteperdrix wrote: >>>>>>>>>> On Fri, Feb 06, 2015 at 04:56:59PM +0100, Anders Blomdell wrote: >>>>>>>>>>> On 2015-02-06 16:49, Philippe Gerum wrote: >>>>>>>>>>>> On 02/06/2015 04:34 PM, Anders Blomdell wrote: >>>>>>>>>>>>> On 2015-02-06 16:11, Philippe Gerum wrote: >>>>>>>>>>>>>> On 02/06/2015 03:47 PM, Anders Blomdell wrote: >>>>>>>>>>>>>>> I have an application that need both realtime and linux sockets, am I correct in assuming that >>>>>>>>>>>>>>> withe the alchemy skin I could access them like >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> socket(... // Linux version >>>>>>>>>>>>>>> __real_socket(... // Linux version >>>>>>>>>>>>>>> __cobalt_socket(... // Alchemy/cobalt version >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> while under the cobalt skin, it would be: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> socket(... // Alchemy/cobalt version >>>>>>>>>>>>>>> __real_socket(... // Linux version >>>>>>>>>>>>>>> __cobalt_socket(... // Alchemy/cobalt version >>>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> This depends on the LDFLAGS retrieved from xeno-config: >>>>>>>>>>>>>> >>>>>>>>>>>>>> 1. with --posix mentioned in the xeno-config --ldflags request >>>>>>>>>>>>>> >>>>>>>>>>>>>> socket(...), __cobalt_socket(...) or __RT(socket(...)) => Cobalt >>>>>>>>>>>>>> implementation >>>>>>>>>>>>>> __real_socket(...) or __STD(socket(...)) => glibc service >>>>>>>>>>>>>> >>>>>>>>>>>>>> 2. without --posix mentioned in the xeno-config --ldflags request >>>>>>>>>>>>>> >>>>>>>>>>>>>> __cobalt_socket(...) or __RT(socket(...)) => Cobalt implementation >>>>>>>>>>>>>> socket(...) or __STD(socket(...)) => glibc service >>>>>>>>>>>>>> >>>>>>>>>>>>>> e.g. >>>>>>>>>>>>>> >>>>>>>>>>>>>> - the application only wants to access the POSIX services implemented by >>>>>>>>>>>>>> Cobalt using the regular POSIX names: LDFLAGS should contain the output of: >>>>>>>>>>>>>> $ xeno-config --posix --ldflags, or --cobalt --ldflags. >>>>>>>>>>>>>> >>>>>>>>>>>>>> - the application wants to access the POSIX services implemented by >>>>>>>>>>>>>> Cobalt using the regular POSIX names, and the alchemy API: LDFLAGS >>>>>>>>>>>>>> should contain the output of: >>>>>>>>>>>>>> $ xeno-config --posix --alchemy --ldflags, or --cobalt --alchemy --ldflags. >>>>>>>>>>>>>> >>>>>>>>>>>>>> - the application wants to access the POSIX services implemented by >>>>>>>>>>>>>> Cobalt solely via the explicit POSIX wrappers, and the alchemy API: >>>>>>>>>>>>>> LDFLAGS should contain the output of (i.e. omitting --posix): >>>>>>>>>>>>>> $ xeno-config --alchemy --ldflags, or --alchemy --ldflags. >>>>>>>>>>>>>> >>>>>>>>>>>>>> NOTE: using __RT() is preferred to calling __cobalt(), in case an API >>>>>>>>>>>>>> stacked over the Cobalt POSIX API redefines its own implementation of >>>>>>>>>>>>>> POSIX services over the dual kernel. __RT() would call the stacked >>>>>>>>>>>>>> implementation, __cobalt() would force a call to the Cobalt >>>>>>>>>>>>>> implementation of the service. >>>>>>>>>>>>>> >>>>>>>>>>>>> Thanks for the clarification, will sprinkle the code with __STD(...) >>>>>>>>>>>>> and __RT(...), from here on :-). >>>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> That's only required if you want your code to unambiguously route to the >>>>>>>>>>>> proper service in case the default symbol wrapping does not fit, or is >>>>>>>>>>>> not present. This is typically what libcopperplate does, so that >>>>>>>>>>>> non-POSIX apps can link against it, without being required to wrap the >>>>>>>>>>>> POSIX symbols in the final executable. >>>>>>>>>>> >>>>>>>>>>> More to avoid me shooting myself in the foot when trying to juggle sockets >>>>>>>>>>> from two different domains (also makes the code less dependent on the linker >>>>>>>>>>> flags given). Already got bitten by 'modprobe rtpacket' not loading properly >>>>>>>>>>> and the __wrap_socket picking up the posix version. And of course making the >>>>>>>>>>> code clearly document what belongs where. >>>>>>>>>> >>>>>>>>>> Not loading rtpacket should cause __wrap_socket to use the posix >>>>>>>>>> version only if you are trying to create a socket type that the >>>>>>>>>> rtpacket module implements. Otherwise, this is a bug. >>>>>>>>> >>>>>>>>> And unless code has changed between 2.x and 3.x in this area, using >>>>>>>>> __RT() will result in exactly the same behaviour. >>>>>>>> >>>>>>>> You might be right, but AFAICT, on 2.6.2.1 'int __rt_dev_socket(...)' >>>>>>>> (ksrc/skins/rtdm/core.c) calls 'struct rtdm_device *get_protocol_device(...)' >>>>>>>> (ksrc/skins/rtdm/device.c), while in xenomai3/next 'COBALT_IMPL(int, socket,...)' >>>>>>>> does a 'XENOMAI_SYSCALL3(sc_cobalt_socket, ...)' and then does a failover to >>>>>>>> '_STD(socket, ...)' in case of -ENOSYS (which is what I believe an unloaded rt_packet.ko >>>>>>>> gives as a result). >>>>>>>> >>>>>>>> Am I missing something obvious? >>>>>>> >>>>>>> You are comparing user-space code with kernel space code. In xenomai >>>>>>> 2.6, the user-space code you should be looking at is >>>>>>> src/skins/posix/rtdm.c >>>>>> Even from native mode (which is what I use in 2.6)? >>>>> >>>>> In that case, you should look at src/skins/rtdm/core.c >>>>> The services rt_dev_socket belongs to the rtdm skin not to native >>>>> skin. >>>> I stand humbly corrected. >>>> >>>>> >>>>>> >>>>>>> And in that code __wrap_socket falls back to __real_socket if the >>>>>>> kernel-space code returns one of the known errors. >>>>>>> >>>>>>> Now the real question is: what arguments do you pass to the cobalt >>>>>>> rt socket call? If these arguments are the one corresponding to the >>>>>>> socket protocol implemented by the rtpacket module, the behaviour >>>>>>> you observe is normal, otherwise, this is a bug. >>>>>> I don't say it's a bug, but to me it seems like alchemy differs from >>>>>> the old native skin in this case. >>>>> >>>>> Well, not really, the native skin never had a socket call anyway, >>>>> and alchemy does not either. It is just that the rtdm skin >>>>> disappeared, so now you use the cobalt service instead of the rtdm >>>>> skin. >>>> # /usr/xenomai/bin/xeno-config --version >>>> 3.0-rc2 >>>> # usr/xenomai/bin/xeno-config --help >>>> Usage xeno-config OPTIONS >>>> Options : >>>> --help >>>> --v,--verbose >>>> --version >>>> --cc >>>> --ccld >>>> --arch >>>> --prefix >>>> --[skin=]posix/cobalt|vxworks|psos|alchemy|rtdm|smokey >>>> >>>> --rtdm is there, bug? >>> >>> The ambiguous rt_dev_*() API has been obsoleted, since any application >>> can now use the POSIX call (all apps have libcobalt underneath). Compat >>> wrappers should be provided by libtrank though, I'll push this before 3.0. >>> >>> We will then have: >>> >>> - rtdm_open/read/write...() => inter-driver calls, kernel-space only >>> - open/read/write...() => RTDM service calls for applications >>> - rt_dev_open/read/write...() => compat wrappers from libtrank to >>> open/read/write...(), for 2.x apps that need them. >> >> Ok, so for libraries where I don't know which skin will be used for linking, the >> best way would be to use __RT(...) for the calls, thereby forcing the symbol >> to be whatever the skin --cflags stipulates (if I don't use __RT, the symbol >> might unwrapped at link time), > > Yes, forcing __RT() is the way to make sure that the wrapper for that > symbol will be called over Cobalt, regardless of whether --wrap was > mentioned in the link flags. Using this in API-neutral libs makes sense. > Over Mercury, __RT() has no effect and just returns the argument unchanged. > > and then do an ioctl(RTIOC_DEVICE_INFO) to check >> that I really got a realtime filedescriptor? >> > > Yes. > Philippe and Gilles: big thanks for the clarifications and patience. /Anders -- Anders Blomdell Email: anders.blomdell@control.lth.se Department of Automatic Control Lund University Phone: +46 46 222 4625 P.O. Box 118 Fax: +46 46 138118 SE-221 00 Lund, Sweden