From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 16 Sep 2019 05:10:42 -0500 (CDT) From: Per Oberg Message-ID: <1762355232.5762576.1568628642606.JavaMail.zimbra@wolfram.com> In-Reply-To: References: <2078452807.5749189.1568619128144.JavaMail.zimbra@wolfram.com> Subject: Re: RTDM open, open_rt, and open_nrt MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: xenomai ----- Den 16 sep 2019, p=C3=A5 kl 11:34, Jan Kiszka jan.kiszka@siemens.com = skrev: > On 16.09.19 09:32, Per Oberg via Xenomai wrote: > > Hello list >> I am trying to understand how rtdm works, and possibly why out of a hist= orical >> context. Perhaps there is a good place to read up on this stuff, then pl= ease > > let me know. > > It seems like in the rtdm-api there is only open, but no open_rt or ope= n_nrt. > > More specifically we have: > > - read_rt / read_nrt > > - recvmsg_rt / recvmsg_nrt > > - ioctl_rt / ioctl_nrt > > - .. etc. >> However, when studying an old xenomai2->3 ported driver it seems like th= ere used >> to be open_rt and open_nrt. The problem I was having before (see my back= ground >> comment below) was because the open had been mapped to the old open_nrt = code, >> which in turned used a rt-lock, thus a mix of the two. When switching to= a > > regular mutex it "worked", as in it didn't complain. >> In a short discussion Jan Kiszka gave me the impression that open could = possibly > > end up being rt or nrt depending on situation. >> P=C3=96: I'm guessing that open is always non-rt and therefore a rtdm_lo= ck should be > > used? ... > > JK: This depends. If the open code needs to synchronize only with other= non-RT > > JK: paths, normal Linux locks are fine. If there is the need to sync wi= th the > > JK: interrupt handler or some of the _rt callbacks, rtdm_lock & Co. is = needed. >> So, how does this work? And why was (if it was) open_nrt and open_rt rep= laced > > with a common open? > The original RTDM design was foreseeing the use case of creating and dest= roying > resources like file descriptors for devices in RT context. That idea was = dropped > as also the trend for the core was clearly making this less realistic. > Therefore, we removed open/socket_rt from Xenomai 3. > If you have a driver that exploited open_rt, you need to remove all rt-sl= eeping > operations from its open function. If rtdm_lock is an appropriate alterna= tive > depends on the driver locking structure and the code run under the lock. > rtdm_lock_get makes the lock holder unpreemptible. So, if rtdm_mutex was = chosen > because of lengthy code under the lock, that would not be a good alternat= ive. > Then we would have to discuss what exactly is run there, and why. Ok, can I read up on this somewhere? I found [1], is that still valid in th= is context? ( Oh, and can we expect a third edition perhaps ? =3D) ) [1] Building Embedded Linux Systems: Concepts, Techniques, Tricks, and Trap= s 2nd Edition, Kindle Edition > > Background > > ---------------- >> I recently wrote about a driver which warned about "drvlib.c:1349 >> rtdm_mutex_timedlock". I got good answers which led me to some more gene= ral >> questions, but instead of continuing in the old tread I thought it bette= r to >> start a new one since it's not about the initial problem. The driver in = case is > > the Peak Linux Driver for their CAN hardware, see [1] > > [1] https://www.peak-system.com/fileadmin/media/linux/index.htm > Did you inform them about their problem already? Maybe they are willing t= o fix > it. We can't, it's not upstream code. No, I haven't, but I will. The reason I haven't yet is because I was under = the impression that this didn't happen to them. I'm trying to compile every= thing (driver, lib, and application) in a Yocto based SDK setup and it seem= s like compilation flags and environment variables are getting squashed in = interesting ways. My reasoning so far was that I got this wrong somehow. Then there's the fact that making it work is only part of the goal. I do re= ally want to understand how this fits together. > Jan > -- > Siemens AG, Corporate Technology, CT RDA IOT SES-DE > Corporate Competence Center Embedded Linux Thanks Per =C3=96berg=20