OpenBSC March 2019

openbsc@lists.osmocom.org

11 participants
28 discussions

RFC: talloc contexts / automatic free at select loop
by Harald Welte 25 Mar '19

25 Mar '19

Hi all, this idea has been floating around for quite some time, and I finally took some time for a proposed implementation: The introduction of a "volatile" talloc context which one can use to allocate whatever temporary things from, and which would automatically be free'd once we leave the select dispatch. The current proposal is in https://gerrit.osmocom.org/#/c/libosmocore/+/13312 and I'm happy to receive any review. How this works: * within a new osmo_select_main_ctx() function, we create a temporary talloc context before calling the filedescriptor call-back functions, and we free that after the call-backs have returned * any of the code running from within the select loop dispatch (which for "normal" osmocom CNI projects is virtually everything) can use that temporary context for allocations. There's a OTC_SELECT #define for convenience. So you could do something like talloc_zero(OTC_SELECT, ...) which would be automatically free'd after the current select loop iteration. Where is this useful? There's at least two common use cases: * allocation of message buffers without having to worry about msgb ownership * various temporary buffers e.g. for something-to-string conversions where currently we use library-internal static buffers with all their known problems (not being able to use them twice within a single printf() statement, not being thread-safe, ...) To Neels' disappointment, this is not all automatic. You a) have to call the _c suffix of the respective function, e.g. osmo_hexdump_c() instead of osmo_hexdump() with one extra initial argument: OTC_SELECT. There's also msgb_alloc_c(), msgb_copy_c() and the like, allowing msgb allocation from a context of your choice, as opposed to the library-internal msgb_tall_ctx that we had so far. b) have to use osmo_select_main_ctx() instead of osmo_select_main(). This is an arbitrary limitation for optimization that Pau requested, to make sure applications that don't want this can avoid all the extra talloc+free at every select iteration. This is debatable, and we can make it automatic in osmo_select_main(). It's probably worth a benchmark how expensive that 'empty' allocation + free is. However, I think that's a rather "OK" price to pay. Converting the existing callers can be more or less done with "sed" (yes, spatch is of course better). While introducing this feature, I also tried to address two other topics, which are not strictly related. However, ignoring those two now would mean we'd have API/ABI breaks if we'd care about them in the future. Hence I think we should resolve them right away: 1) introduce another context: OTC_GLOBAL. This is basically a library-internal replacement for the "g_tall_ctx" that we typically generate as one of the first things in every application. You can use it anywhere where you'd want to allocate something form the global talloc context 2) make those contexts thread-local. As you may know, talloc is not thread safe. So you cannot allocate/free from a single context on multiple threds. However, it is safe to have separate talloc contexts on each thread. Making the new OTC_* contexts per-thread, we are enabling the [limited] use of this functionality in multi-threaded programs. This is of course very far from making libosmocore thread-safe. There are many library-internal data structures like timers, file descriptors, the VTY, ... which are absolutely not thread-safe. However, I think it's a step in the right direction and I don't expect any performance impact for single-threaded programs by marking the contexts as __thread. -- - Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/ ============================================================================ "Privacy in residential applications is a desirable marketing option." (ETSI EN 300 175-7 Ch. A6)

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OSMO SMSc functionality
by Alex Alwin Thomas 23 Mar '19

23 Mar '19

Hi, We had a question with regards to the OSMO MSc - as per the documentation , it does support a scaled down version of SMSC. Can we bring up just the SMSc service so that it can talk to another vendor's MSC/HLR . We are trying to perform CSFB SMS tests with an external MSC / OSMO SMSC and Amarisoft EPC Core . So wanted to check if the OSMO SMSC could be used for this test. Thanks Alex

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"signal.c: Make non-exported tall_sigh_ctx static" broke openbsc
by Oliver Smith 22 Mar '19

22 Mar '19

Hello, openbsc.git doesn't build anymore against libosmocore master: > ../../src/libcommon/libcommon.a(talloc_ctx.o): In function `talloc_ctx_init': > /build/openbsc/src/libcommon/talloc_ctx.c:50: undefined reference to `tall_sigh_ctx' Full build log: https://jenkins.osmocom.org/jenkins/job/master-openbsc/IU=--disable-iu,MGCP… Looks like this patch broke it: https://gerrit.osmocom.org/#/c/libosmocore/+/13337/ Regards, Oliver -- - Oliver Smith <osmith(a)sysmocom.de> https://www.sysmocom.de/ ======================================================================= * sysmocom - systems for mobile communications GmbH * Alt-Moabit 93 * 10559 Berlin, Germany * Sitz / Registered office: Berlin, HRB 134158 B * Geschaeftsfuehrer / Managing Director: Harald Welte

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TTCN-3 L1CTL-related test issue
by Max 20 Mar '19

20 Mar '19

Hi. While experimenting with BTS TTCN-3 tests I've got some of the tests misteriously failing with: FBSB Failed with non-zero return code 255 Anyone hit this before? Any ideas what could be causing this? -- - Max Suraev <msuraev(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * sysmocom - systems for mobile communications GmbH * Alt-Moabit 93 * 10559 Berlin, Germany * Sitz / Registered office: Berlin, HRB 134158 B * Geschaeftsfuehrer / Managing Directors: Harald Welte

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SCCP connection identifiers vs. local references
by Harald Welte 20 Mar '19

20 Mar '19

Hi Neels, > 21:14 < neeels> LaF0rge, I need a solution for picking a conn_id as an SCCP SAP user. The way osmo-bsc > does it isn't much good either. There has to be some way to obtain an unused local > reference without running into potential collisions > 21:16 < neeels> (I submitted the patch expecting your -1, but just to make sure that I understood > correctly I wanted to submit as code that has no room for misunderstandings) > 21:18 < neeels> if I can't use the internal "next_id" thing, then what I would have to do is mimick the > exact same in osmo-msc by looking up what conn_ids are already in use and pick an unused > one. That's quite brain damaged IMHO, it's the same thing as that layer violation patch, > only with much more effort and more chances for id collisions. Nobody is suggesting that. > 21:21 < neeels> ideas: add some primitive to hand out a local reference -- but that would be non-standard > IIUC I had mentioned and discarded that option in Message-ID: <20190311204817.GA725@nataraja> here on this list. The reason is not that it's non-standard, but that it again wouldn't work over any type of asynchronous / message based SAP [and that's how a SAP is conceptualized]. > 21:21 < neeels> give each application some unique number space for local references, like the highest > byte is configured in .cfg file, and then each SCCP user cycles through its own number > space of local references > 21:23 < neeels> ...and libosmo-sccp would have to be constrain-able to its own number space for incoming > connections I was quite sure we've had that discussion before. Unfortuantely it doesn't seem to be on this mailing list or in gerrit. It may have been on IRC or I am starting to be delusional :/ The correct solution from the spec / SCCP architecutre point of view is rather clear, I think: * don't recycle the SCCP local reference (protocol) from the SCCP connection ID (SAP), but use distinct number spaces for that. It was an oversimplification to do that in the original implementation. I simply missed the different scoping of those two identifiers. The scoping is the root of our problems here. * only once we have distinct identifiers, we can fix the scope: One of the two identifiers has a per-SCCP-user scope, while the other has a per-SCCP-instance scope * this way, every SCCP user knows exactly which SCCP connection identifiers are currently in use between this specific user and the SCCP provider, and it hence can choose any unused ID for a new connection * right now, the primitive exchange across the SCCP user SAP is synchronous, so there can be no races where the SCCP provider and the SCCP user could chose the same connection ID at the same time. If you want to prepare for some kind of possible future asynchronous, message-queue based SAP, then you could use the highest bit as "allocation flag", e.g. highest bit = 0, allocated by the SCCP provider and highest bit = 1, allocated by SCCP user. Let me know if you see any problem with above proposal. Regards, Harald -- - Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/ ============================================================================ "Privacy in residential applications is a desirable marketing option." (ETSI EN 300 175-7 Ch. A6)

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jenkins: master-libosmocore running for 20 hours
by Oliver Smith 20 Mar '19

20 Mar '19

Hi all, master-libosmocore was running for 20 hours on jenkins, hanging here: > make[7]: Entering directory '/home/osmocom-build/jenkins/workspace/master-libosmocore/a2/default/a3/default/a4/default/arch/amd64/label/osmocom-master-debian9/builddir/tests' > osmo_verify_transcript_vty.py -v \ > -p 42042 \ > -r "../tests/tdef/tdef_vty_test_config_root" \ > /home/osmocom-build/jenkins/workspace/master-libosmocore/a2/default/a3/default/a4/default/arch/amd64/label/osmocom-master-debian9/tests/tdef/tdef_vty_test_config_root.vty > <0000> /home/osmocom-build/jenkins/workspace/master-libosmocore/a2/default/a3/default/a4/default/arch/amd64/label/osmocom-master-debian9/src/socket.c:367 unable to bind socket:127.0.0.1:42042: Address already in use > [0;m<0000> /home/osmocom-build/jenkins/workspace/master-libosmocore/a2/default/a3/default/a4/default/arch/amd64/label/osmocom-master-debian9/src/socket.c:378 no suitable addr found for: 127.0.0.1:42042 > [0;m<0000> /home/osmocom-build/jenkins/workspace/master-libosmocore/a2/default/a3/default/a4/default/arch/amd64/label/osmocom-master-debian9/src/vty/telnet_interface.c:100 Cannot bind telnet at 127.0.0.1 42042 https://jenkins.osmocom.org/jenkins/job/master-libosmocore/a2=default,a3=de… I've stopped the job. Right after that, a new job spawned, and it also failed to bind telnet at 42042. It did not hang this time, but stopped there instead: https://jenkins.osmocom.org/jenkins/job/master-libosmocore/a2=default,a3=de… After triggering the job once more manually, it went through. >From a quick analysis, I can not see why this has happened in the first place. The master-libosmocore job is set to non-concurrent: https://git.osmocom.org/osmo-ci/tree/jobs/master-builds.yml And the gerrit verification jobs are running on another machine. Other than that, none but libosamocore.git of the (almost all) Osmocom repositories that I have checked out mention port 42042, so nothing else should bind that in theory. Regards, Oliver -- - Oliver Smith <osmith(a)sysmocom.de> https://www.sysmocom.de/ ======================================================================= * sysmocom - systems for mobile communications GmbH * Alt-Moabit 93 * 10559 Berlin, Germany * Sitz / Registered office: Berlin, HRB 134158 B * Geschaeftsfuehrer / Managing Director: Harald Welte

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easier way to avoid msgb leaks in libosmo-sccp callers?
by Neels Hofmeyr 19 Mar '19

19 Mar '19

Avoiding msgb leaks is easiest if the caller retains ownership of the msgb. Take this hypothetical chain where leaks are obviously avoided: void send() { msg = msgb_alloc(); dispatch(msg); msgb_free(msg); } void dispatch(msg) { osmo_fsm_inst_dispatch(fi, msg); } void fi_on_event(fi, data) { if (socket_is_ok) socket_write((struct msgb*)data); } void socket_write(msgb) { if (!ok1) return; if (ok2) { if (!ok3) return; write(sock, msg->data); } } However, if the caller passes ownership down to the msgb consumer, things become nightmarishly complex: void send() { msg = msgb_alloc(); rc = dispatch(msg); /* dispatching event failed? */ if (rc) msgb_free(msg); } int dispatch(msg) { if (osmo_fsm_inst_dispatch(fi, msg)) return -1; if (something_else()) return -1; // <-- double free! } void fi_on_event(fi, data) { if (socket_is_ok) { socket_write((struct msgb*)data); else /* socket didn't consume? */ msgb_free(data); } int socket_write(msgb) { if (!ok1) return -1; // <-- leak! if (ok2) { if (!ok3) goto out; write(sock, msg->data); } out: msgb_free(msg); return -2; } If any link in this call chain fails to be aware of the importance to return a failed RC or to free a msgb if the chain is broken, we have a hidden msgb leak. This is the case with osmo_sccp_user_sap_down(). In new osmo-msc, passing data through various FSM instances, there is high potential for leak/double-free bugs. A very large brain is required to track down every msgb path. Isn't it possible to provide osmo_sccp_user_sap_down() in the caller-owns paradigm? Thinking about an osmo_sccp_user_sap_down2() that simply doesn't msgb_free(). Passing ownership to the consumer is imperative if a msg queue is involved that might send out asynchronously. (A workaround could be to copy the message before passing into the wqueue.) However, looks to me like no osmo_wqueue is involved in osmo_sccp_user_sap_down()? It already frees the msgb right upon returning, so this should be perfectly fine -- right? I think I'll just try it, but if anyone knows a definite reason why this will not work, please let me know. (Remotely related, I also still have this potential xua msg leak fix lying around, never got around to verify it: https://gerrit.osmocom.org/#/c/libosmo-sccp/+/9957/ ) ~N -- - Neels Hofmeyr <nhofmeyr(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * sysmocom - systems for mobile communications GmbH * Alt-Moabit 93 * 10559 Berlin, Germany * Sitz / Registered office: Berlin, HRB 134158 B * Geschäftsführer / Managing Directors: Harald Welte

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osmo-bsc voice assignment broken by 'assignment_fsm: Properly support assigning signalling mode TCH/x'
by Neels Hofmeyr 15 Mar '19

15 Mar '19

Hi Sylvain, completely unrelated to the osmo-msc patch, your other patch that was merged to osmo-bsc breaks voice channel assignment, and I had to revert it. Mentioned so on IRC, but since you didn't reply I thought it best to also post this here: tnt, I think you broke voice Assignment in osmo-bsc. Can't get a voice call in current master. It works again if I revert 4d3a21269b25e7164a94fa8ce3ad67ff80904aee tnt, I'm choosing to revert this from current master now; let's fix it, test and the re-apply the patch when it is ready https://gerrit.osmocom.org/c/osmo-bsc/+/13256 I hope I'm not annoying you by annulling all of your patches :P It's definitely not on purpose! ~N

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merge conflicts in osmo-msc
by Neels Hofmeyr 14 Mar '19

14 Mar '19

Hi everyone, and in this particular case Sylvain, I know I'm hogging osmo-msc.git and I don't intend to hinder everyone else's work, but I doubt that it was really necessary to merge the silent call channel types patch to master right now. I'm really overloaded with doing the inter-MSC handover work, I'm again postponing my well earned leave that I would have liked to have started two months ago, and I don't want to be burdened with also resolving everyone else's merge conflicts. You all know that pretty much everything changes in osmo-msc, even if only slightly. As a rule of thumb, if you see a 'ran_conn', 'vlr_subscr_get()', a Paging callback function or a 'gsm_trans' in a bit of code, likely there will be merge conflicts with my current branch. Most should be trivial, but they will be stones put in my way. So please, before you merge onto master, consider doing the same work on the tip of my branch 'neels/ho' in osmo-msc, rather than on current master. That would be the ideal situation for me, because then you also test my patches. There still is ongoing work at the tip of neels/ho, if you want a more stable point to apply modifications to, look at the commit 'add LOG_TRANS, proper context for all transactions' and rebase your changes onto that. If you push those changes onto a private branch, I will even see them in tig and can simply incorporate them in by branch, carrying them along until we're ready to merge. If you prefer working on master, still do me a favor: just try to rebase the patch onto neels/ho. All the conflicts that you see in such a rebase will end up on my table and stop me from going forward until I have resolved them. Consider that before you hit that "Submit" button on gerrit in the osmo-msc.git repository. Plus, if I resolve conflicts with *your* code, likely I won't grok some minor detail and introduce bugs. So let's work together on this. Thanks! Working on osmo-msc.git neels/ho branch also needs various patches in other repositories; all these branches are kept up-to-date every day and all the time: libosmocore neels/misc libosmo-sccp neels/conn_id osmo-mgw neels/endpoint_fsm osmo-msc neels/ho Thanks again! ~N

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ttcn3: more than one BSC
by Neels Hofmeyr 12 Mar '19

12 Mar '19

I'm trying to test inter-BSC Handover in ttcn3. At first I had problems grasping the concepts, but in the end it worked pretty nicely to start two distinct BSC handlers like this: testcase TC_ho_inter_bsc() runs on MTC_CT { var BSC_ConnHdlr vc_conn0; var BSC_ConnHdlr vc_conn1; f_init(2); vc_conn0 := f_start_handler(refers(f_tc_ho_inter_bsc0), 53, 0); vc_conn1 := f_start_handler(refers(f_tc_ho_inter_bsc1), 53, 1); vc_conn0.done; vc_conn1.done; } It's walking all the way through inter-BSC Handover now (!) up until the point where I want to discard the call. Now I'm facing the simple problem that I want to call f_call_hangup() in the second f_tc_ho_inter_bsc1() -- but I have no cpars (CallParameters) with a valid MNCC callref nor the CC transaction ID, those are in the first function. How can I share cpars between those functions? The transaction_id and callref determined by the MNCC and CC messages that happened in f_tc_ho_inter_bsc0 need to move over to f_tc_ho_inter_bsc1, much like the MS has moved to the other BSC. So it would make sense to have some global struct representing the MS which both BSC_ConnHdlr instances can access, if that is at all possible ... ? As a bit of a weak workaround, I could inter-BSC handover right back to the first BSC and then f_call_hangup() there :P ~N -- - Neels Hofmeyr <nhofmeyr(a)sysmocom.de> http://www.sysmocom.de/ ======================================================================= * sysmocom - systems for mobile communications GmbH * Alt-Moabit 93 * 10559 Berlin, Germany * Sitz / Registered office: Berlin, HRB 134158 B * Geschäftsführer / Managing Directors: Harald Welte

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OpenBSC March 2019