[CRIU] two runc related questions (-d and read-only)

[Adrian Reber]

On Wed, Sep 14, 2016 at 05:45:49AM -0700, Andrei Vagin wrote:
> On Mon, Sep 12, 2016 at 07:41:29PM +0200, Adrian Reber wrote:
> > I was trying to checkpoint and restore a runc container and so far I had
> > two smaller problems. My runc container has
> > 
> > 	"terminal": false
> > 
> > and I am starting it detached '-d'. Checkpointing this container fails
> > if I run 'runc checkpoint --shell-job test' or without '--shell-job'
> > with following error:
> > 
> > (00.003008) 29213 fdinfo 0: pos: 0x               0 flags: 102002/0
> > (00.003022) tty: Dumping tty 8 with id 0x7
> > (00.003026) Error (files-reg.c:1141): Can't lookup mount=22 for fd=0 path=/dev/pts/2
> > (00.003029) ----------------------------------------
> > (00.003071) Error (cr-dump.c:1296): Dump files (pid: 29213) failed with -1
> > 
> > I get the same error using criu-2.4 and latest master. If I start the
> > container without '-d' I can checkpoint it without any problem.
> 
> Could you try to run ./runc ... &> /dev/null  < /dev/null? Will it help?

Yes, that works.

> Could you show lsof -p for an init process of a container?

This is without the /dev/null redirection you suggested:

COMMAND  PID USER   FD   TYPE DEVICE SIZE/OFF      NODE NAME
start   7464 root  cwd    DIR  252,1     4096   9129255 /
start   7464 root  rtd    DIR  252,1     4096   9129255 /
start   7464 root  txt    REG  252,1   960376 192967906 /usr/bin/bash
start   7464 root  mem    REG  252,1          193825299 /usr/lib64/libnss_files-2.17.so (path inode=16885464)
start   7464 root  mem    REG  252,1          193773498 /usr/lib64/libc-2.17.so (path inode=16883722)
start   7464 root  mem    REG  252,1          193825248 /usr/lib64/libdl-2.17.so (path inode=16884707)
start   7464 root  mem    REG  252,1          193825325 /usr/lib64/libtinfo.so.5.9 (path inode=16860633)
start   7464 root  mem    REG  252,1          193773472 /usr/lib64/ld-2.17.so (path inode=16820578)
start   7464 root    0u   CHR  136,2      0t0         5 /dev/pts/2
start   7464 root    1u   CHR  136,2      0t0         5 /dev/pts/2
start   7464 root    2u   CHR  136,2      0t0         5 /dev/pts/2
start   7464 root  255r   REG  252,1       83   8550670 /start


> > Another problem I have seen is using runc with
> > 
> > 	"readonly": true
> > 
> > this gives me following error:
> > 
> > (00.079785) Dumping task cwd id 0xb root id 0xb
> > (00.079931) mnt: Dumping mountpoints
> > (00.079934) mnt: 	213: 2b:/null @ ./proc/sched_debug
> > (00.079934) mnt: Something is mounted on top of ./dev
> > (00.080004) Error (criu/mount.c:1044): mnt: Can't create a temporary directory: Read-only file system
> 
> It's known issue. Yesterday I started to rework mount.c to support this
> case. I will try to prepare draft patches before Friday.

Great, good to know.

		Adrian