Re: [PATCH v28 0/8] Timestamp synchronization of host - guest tracing session

[Dario Faggioli <dfaggioli@suse.com>]

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Hello,

On Mon, 2021-02-08 at 08:17 +0200, Tzvetomir Stoyanov (VMware) wrote:
> Basic infrastructure for host - guest timestamp synchronization and a
> PoC implementation of PTP-like and KVM algorithms. 
> 
I'm trying to play with trace-cmd agent & clock syncronization, so I
applied this series.

However, when I try to connect to a VM where I have the agent running,
I'm seeing this (on the host):

# ./tracecmd/trace-cmd record --debug -p nop -e sched:* -e kvm:* -e timer:hrtimer* -A tumbleweed-jeos:8888 -e all sleep 1
trace-cmd: No such file or directory
  Failed to receive trace response -107

I tried to do a strace, still on the host, and this is what I see (the
last part of the output):

rt_sigaction(SIGINT, {sa_handler=0x4116a5, sa_mask=[INT], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x7f29f1b55b70}, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
openat(AT_FDCWD, "/var/lib/trace-cmd/virt/(null)/trace-pipe-cpu0.out", O_RDONLY|O_NONBLOCK) = -1 ENOENT (No such file or directory)
socket(AF_VSOCK, SOCK_STREAM, 0)        = 4
connect(4, {sa_family=AF_VSOCK, sa_data="\0\0\270\"\0\0\3\0\0\0\0\0\0\0"}, 16) = 0
openat(AT_FDCWD, "/sys/kernel/debug/tracing/trace_clock", O_RDONLY) = 6
read(6, "local global counter uptime perf"..., 8192) = 62
read(6, "", 8192)                       = 0
close(6)                                = 0
write(4, "\0\0\0<\0\0\0\6\0\0\0\20\0\0\0\0\0\0\0\0\347\366+n\204\271\35\334", 28) = 28
write(4, "\0\0\0\0\0\0\0\v\0\0\0\2-e\0all\0\0\0\0\1\0\0\0\5ptp\0\0", 32) = 32
read(4, "", 12)                         = 0
dup(2)                                  = 6
fcntl(6, F_GETFL)                       = 0x402 (flags O_RDWR|O_APPEND)
fstat(6, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x9), ...}) = 0
write(6, "trace-cmd: No such file or direc"..., 37trace-cmd: No such file or directory
) = 37
close(6)                                = 0
write(2, "  ", 2  )                       = 2
write(2, "Failed to receive trace response"..., 37Failed to receive trace response -107) = 37
write(2, "\n", 1
)                       = 1
exit_group(2)                           = ?
+++ exited with 2 +++

Finally, if I use `--debug` both on the host and in the VM, here's what
I get.

Guest:
# ./tracecmd/trace-cmd agent -p 8888 --debug
listening on @3:8888
msg received: 6 (TRACE_REQ) [60]
Segmentation fault

Host:
# ./tracecmd/trace-cmd record --debug -p nop -e sched:* -e kvm:* -e timer:hrtimer* -A tumbleweed-jeos:8888 -e all sleep 1
msg send: 6 (TRACE_REQ) [60]
trace-cmd: No such file or directory
  Failed to receive trace response -107

Am I doing something wrong? :-)

If necessary, I can provide more info about my setup, or do more tests.

Thanks and Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

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