[lttng-dev] Problem to get lttng work with a daemon application

[Mathieu Desnoyers]

* Hans Nordebäck (hans.nordeback at ericsson.com) wrote:
> Hi, I've just started using lttng and run it in Ubuntu 12.04 in VirtualBox.
>
> I have run the sample applications without any problem, but I have  
> problems to get a daemon application work.
>
> I have added tracepoint support in the same way as for the sample  
> applications and do the following:
>
> 1) The lttng-sessiond (version 2.0.1) is started (with  

2.0.1 is old. Please upgrade to the latest versions of the 2.0.x series
for both lttng-tools and lttng-ust and try again.

Thanks,

Mathieu

> --verbose--verbose-consumer).
> 2) I start the daemon application with one tracepoint implemented.
> 3) I can see that the lttng-sessiond gets called regarding this tracepoint:
>
> DEBUG1: App registered with pid:18421 ppid:18419 uid:0 gid:0 sock:18  
> name:osafamfnd (version 2.0) [in ust_app_register() at ust-app.c:1365]
>
> 4) I run, strace -f lttng -v list -u, and can see that it "hangs" in  
> recvmsg:
> write(2, "DEBUG1: Getting UST tracing even"..., 81DEBUG1: Getting UST  
> tracing events [in list_ust_events() at     commands/list.c:253]
> ) = 81
> getuid()                                = 0
> socket(PF_FILE, SOCK_STREAM, 0)         = 3
> connect(3, {sa_family=AF_FILE,  
> path="/var/run/lttng/client-lttng-sessiond"}, 110) = 0
> geteuid()                               = 0
> getegid()                               = 0
> sendmsg(3, {msg_name(0)=NULL,  
> msg_iov(1)=[{"\16\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 
> 8784}], msg_controllen=28, {cmsg_len=28, cmsg_level=SOL_SOCKET,  
> cmsg_type=SCM_CREDENTIALS{pid=28878, uid=0, gid=0}}, msg_flags=0}, 0) = 
> 8784
> recvmsg(3,
>
> 5) the lttng-sessiond outputs only the following and hangs as long as  
> the daemon application is running.
> DEBUG1: Processing client command 14 [in process_client_msg() at  
> main.c:3309]
>
> 6) The only difference between sample app logs and daemon app logs is  
> that the pid and ppid seen at DEBUG1: App registered. In the daemon case  
> in this run it is pid 18421 ppid 18419 but when I print it in the  
> function calling tracepoint
> it is pid 18430. I don't know if that is related to the problem. Any  
> help on this would be appreciated.
>
> /Thanks Hans
>
>
>
>
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-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com