Re: qemu couldn't connect the unix domain socket

[Li Feng <fengli@smartx.com>]

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On Fri, Oct 29, 2021 at 5:34 PM Stefano Brivio <sbrivio(a)redhat.com> wrote:
>
> On Fri, 29 Oct 2021 16:54:47 +0800
> Li Feng <fengli(a)smartx.com> wrote:
>
> > [...]
> >
> > Thanks for the detailed explanation.
> > I finally found out that the `qrap` was the root cause.
> > I patched the qemu, and it works well.
>
> Have you found out what was the offending syscall? I'll probably hit
> this later too, but that would help me double checking what the problem
> was.

I made a mistake in the previous mail, using `./passt -f` works, but
if running in background,
it still exits without any output.

This is the strace output.

```
$ strace -f ./passt
...
...
accept(6, NULL, NULL)                   = 7
epoll_ctl(5, EPOLL_CTL_ADD, 7, {events=EPOLLIN|EPOLLRDHUP|EPOLLET,
data={u32=7, u64=7}}) = 0
getrandom("\x40\xfc\xc5\x4a\x29\x3e\xdb\xcd\x25\x92\xc6\xc3\xc7\xcb\x57\x5a",
16, GRND_RANDOM) = 16
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 8
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 9
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 10
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 11
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 12
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 13
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 14
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 15
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 16
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 17
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 18
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 19
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 20
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 21
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 22
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 23
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 24
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 25
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 26
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 27
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 28
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 29
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 30
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 31
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 32
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 33
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 34
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 35
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 36
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 37
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 38
socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 39
clone(child_stack=NULL,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLDstrace: Process
172939 attached
, child_tidptr=0x7f7b89b1da10) = 172939
[pid 172921] exit_group(0 <unfinished ...>
[pid 172939] set_robust_list(0x7f7b89b1da20, 24 <unfinished ...>
[pid 172921] <... exit_group resumed>)  = ?
[pid 172921] +++ exited with 0 +++
<... set_robust_list resumed>)          = ?
+++ killed by SIGSYS (core dumped) +++
```
Which is the bad syscall?

>
> > [...]
> >
> > This background knowledge helped me a lot.
> > The seccomp works well with Fedora 35 without the `qrap`.
> > Thanks again for your great work.
>
> You're welcome, I'm glad to hear it works for you!
>
> --
> Stefano
>