Re: qemu couldn't connect the unix domain socket

[Stefano Brivio <sbrivio@redhat.com>]

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On Fri, 29 Oct 2021 19:02:15 +0800
Li Feng <fengli(a)smartx.com> wrote:

> 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?

Oh, it's set_robust_list(), it's normal that exit_group() doesn't
return. That new usage probably comes from:
	https://sourceware.org/git/?p=glibc.git;a=commit;h=9a7565403758f65c07fe3705e966381d9cfd35b6

and that code path is not really needed for passt, so I would have a
quick try at avoiding it rather than adding a syscall, perhaps with a
small replacement of daemon() using clone() instead of fork().

Meanwhile, this should work for you:

diff --git a/passt.c b/passt.c
index 6436a45..2a4ba8b 100644
--- a/passt.c
+++ b/passt.c
@@ -280,3 +280,3 @@ static void pid_file(struct ctx *c) {
  * #syscalls openat fstat fcntl lseek clone setsid exit_group getpid
- * #syscalls clock_gettime newfstatat
+ * #syscalls clock_gettime newfstatat set_robust_list
  * #syscalls:pasta rt_sigreturn

-- 
@@ -280,3 +280,3 @@ static void pid_file(struct ctx *c) {
  * #syscalls openat fstat fcntl lseek clone setsid exit_group getpid
- * #syscalls clock_gettime newfstatat
+ * #syscalls clock_gettime newfstatat set_robust_list
  * #syscalls:pasta rt_sigreturn

-- 
Stefano