l4-hackers June 2014

l4-hackers@os.inf.tu-dresden.de

24 participants
33 discussions

A conceptual question about IPC
by Jorge Ventura 24 Jun '14

24 Jun '14

I have been reading several papers about micro kernel and they explain how critical the IPC design is for kernel performance, most of them point to use of register, incomplete context switch and so on. Here is my question: Is not possible to use the MMU and just execute a page swap between address spaces ? Make changes in the page table is not something fast ?

2 1

Setting task priority in loader configuration script
by Peter Howard 24 Jun '14

24 Jun '14

Dear all, I've looked through the documentation, but it doesn't seem clear how you set the priority of a task as you create it from a .cfg script. I've tried: loader:start({caps = { ... }, l4re_dbg = L4.Dbg.Warn, log = {"foo", "red" }, priority = 100}, "rom/foo"); But I'm not seeing any difference from that, with priority < 0x10, > 0x10, or unset. (I got the 0x10 value from http://os.inf.tu-dresden.de/l4env/doc/html/loader/p_script.html) So, is that the correct way? If now, what is the correct way to specify priority? Thanks, -- Peter Howard <pjh(a)northern-ridge.com.au>

2 3

Fwd: l4shmnet and its structure
by cem akpolat 22 Jun '14

22 Jun '14

Hi, "So I understand that you configured one L4Linux with two l4shmnet network interfaces and one of those two did not work? Hard to tell for me what's wrong without more info." I added printf lines to shmc.c file and the output I get the following output while a connection is created btw. the server and the first client. //*************************************// client1 | l4shmc_create : starting client1 | l4shmc_create : l4re_ns_register_obj_srv returned error client1 | l4shmc_attach_to : starting client1 | l4shmc_attach_to : no problem, returning L4_OK client1 | l4shmc_add_chunk : starting client1 | l4shmc_add_chunk : executing chunk_get client1 | l4shmc_add_chunk : in the else side due to offs client1 | l4shmc_add_chunk : returning L4_OK client1 | l4shmc_add_signal : starting client1 | l4shmc_add_signal : returning L4_EOK client1 | l4shmc_get_chunk_to :starting server | l4shmc_get_chunk_to :starting net shm0: shm0: L4ShmNet established, with 54:42:00:00:ff:01, IRQ 66 client1 net shm0: shm0: L4ShmNet established, with 54:42:00:00:ff:02, IRQ 65 And the following output between the server and the second client: //*************************************// client2 | l4shmc_create : starting client2 | l4shmc_create : l4re_ns_register_obj_srv returned error client2 | l4shmc_attach_to : starting client2 | l4shmc_attach_to : no problem, returning L4_OK client2 | l4shmc_add_chunk : starting client2 | l4shmc_add_chunk : executing chunk_get client2 | l4shmc_add_chunk : in the else side due to offs client2 | l4shmc_add_chunk : returning L4_OK client2 | l4shmc_add_signal : starting client2 | l4shmc_add_signal : returning L4_EOK client2 | l4shmc_get_chunk_to :starting server | l4shmc_get_chunk_to :starting net shm1: shm1: L4ShmNet established, with 54:42:00:00:ff:04, IRQ 67 //*************************************// As you can see, the second client does not respond after the connection established message from the server. I have two questions regarding this problem: 1) Is the message "l4re_ns_register_obj_srv returned error" the source of the problem? If so, then what might be the reason for this error? And also, why does the connection work properly between the first server and the client if that is the source of the problem? 2) Could it be the case that the second client obtains the same IRQ number with the first client(IRQ 65) or the server (IRQ66 or 67), and therefore the trigger signal is not received by the second client? How can I detect this problem? Which function is responsible for the IRQ numbering? As you can see, the second client does not respond after the connection established message from the server. I have two questions regarding this problem: 1) Is the message "l4re_ns_register_obj_srv returned error" the source of the problem? If so, then what might be the reason for this error? And also, why does the connection work properly between the first server and the client if that is the source of the problem? 2) Could it be the case that the second client obtains the same IRQ number with the first client(IRQ 65) or the server (IRQ66 or 67), and therefore the trigger signal is not received by the second client? How can I detect this problem? Which function is responsible for the IRQ numbering? Thank you very much for your time, Cem

2 3

RCU period
by Yuxin Ren 22 Jun '14

22 Jun '14

Hi I do not understand the period in Rcu class. How do we use it? Now it is 10ms, how is it calculated? Thanks a lot.

2 3

How does Fiasco implement printf
by Yuxin Ren 22 Jun '14

22 Jun '14

Hi, I think printf usually invoke system call. But in Fiasco only one system call is capability invocation. So what capability is invoked by printf? Or Fiasco implements printf in user level, so printf triggers a normal IPC? Thank you. Best

3 2

Question about seL4 on July 29th
by Jorge Ventura 21 Jun '14

21 Jun '14

Anybody knows what kind of Open Source License is expected to be deployed with seL4 on July 29th ?

3 2

Istream beginner help
by ba_f 17 Jun '14

17 Jun '14

Hallo Hackers, for design reason i would like to use separate Istream & Ostream instead of IOstream with call(). ostream.send() does work, but i cant manage istream.receive(). It keeps waiting for ever. I did edit the client from pkg/examples/clntsrv, the server sends the result, so there should be something to receive. What am i missing? // pkg/examples/clntsrv/myClient.cc static L4::Cap<void> server; static int func_neg_transmit() { L4::Ipc::Ostream oStream(l4_utcb()); l4_uint32_t val = 8; s << l4_umword_t(Opcode::func_neg) << val; int r = l4_error(s.send(server.cap(), Protocol::Calc)); } static int getResult() { L4::Ipc::Istream iStream(l4_utcb()); l4_uint32_t val; // while ( iStream.has_more<l4_uint32_t>()) { // doesnt work neither int r = l4_error(iStream.receive(server.cap())); printf("receive success\n"); // doesnt pass here iStream >> val; } int main() { server = L4Re::Env::env()->get_cap<void>("calc_server"); func_neg_transmit(); getResult(); return 0; } THANK YOU

2 1

Multiple IPC_Gate channels per task
by professor xavier 13 Jun '14

13 Jun '14

Hi, I am a newbie to L4 and have a simple question about the IPC_Gate feature. Can a single task support multiple IPC_Gates? If so, can you please provide an example of a *.cfg script that shows this? Thank you. px

2 1

l4shmnet and its structure
by cem akpolat 13 Jun '14

13 Jun '14

Dear all, As far as I tested, l4smnet.c file establishes a communication channel between client ann server l4linux and I asked couple of weeks ago about the posibility of multiple clients and one server example and Adam recommended me to use one of the l4linux, in this case server, as a router. That is exactly the way that I am following. For this reason, I tried first of all a simple example: one server two clients with two different shm. Interestingly, I couldn't see the second client. I couldn't evaluate whether this trial was logical or not, but if this works for one of the clients why not for the second? Apart from this case, I attempt to convert l4shmnet from two l4linux to multiple case, but this is really not easy. I tried one shared memory first of all, modifying some parts of the code is quite difficult, you can easily encounter a failure such as page_fault. That's why I did two shared memory as mentioned above. My simple question, which way is really more logical, 1- using one shared memory for all clients and server or 2- multiple shared memory for each separate client. Is there any document or source snippet that I can to use a similar structure in l4re. shm code is already here, but it doesn't really give insight into this part. Thanks, Best Regards, Cem Akpolat

2 1

Trouble building l4linux
by Sören Jonsson 10 Jun '14

10 Jun '14

Hello, I have successfully built L4Fiasco and L4Re, and tested it by running the hello test program under quemu. After that I attempted to build L4linux, using instructions from this site: http://wiki.tudos.org/L4Linux/build . Unfortunately, when I came to the stage of "make O=/home/osj/l4linux_bld/" I get an error message "make[2]: *** [/home/osj/l4/l4linux_bld/Makeconf.l4conf] Error 1 make[1]: *** No rule for creating the target "/home/osj/l4/l4linux_bld/Makeconf.l4conf" Is there another web page I should get my instructions from, or is there anything I have missed in my attempt to build l4linux? Best regards, Sören Jonsson Sweden

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l4-hackers June 2014