Re: [uml-user] invalid /proc/PID/exe in UML processes

[Richard W. <ric...@gm...>]

On Mon, Jun 2, 2014 at 7:55 PM, Nalli, Sanketh <san...@hp...> wrote:
> Thanks a lot.
>
> Do you know why my /proc is empty in the guest

Did you mount procfs?

> And why does the /proc/PID/exe NOT point to anything in
>
> The host ? (PID is the pid of a dummy program running in UML)

Host PID != Guest PID

>
>
> From: enjoy mindful [mailto:enj...@gm...]
> Sent: Friday, May 30, 2014 12:06 AM
> To: Nalli, Sanketh
> Cc: use...@li...
> Subject: Re: [uml-user] invalid /proc/PID/exe in UML processes
>
>
>
> let me answer your second question.
>
> I did this analysis with kernel linux-3.12.6:
>
> 1) make ARCH=um cscope
> 2) search functions which called 'clone'
>   File       Function        Line
> 0 ubd_user.c start_io_thread   43 pid = clone(io_thread, (void *) sp,
> CLONE_FILES |
>                                   CLONE_VM, NULL);
> 1 helper.c   start_io_thread   74 pid = clone(helper_child, (void *) sp,
> CLONE_VM, &data);
> 2 helper.c   start_io_thread  124 pid = clone(proc, (void *) sp, flags,
> arg);
> 3 process.c  start_userspace  300 pid = clone(userspace_tramp, (void *) sp,
> flags, (void *)
>                                   stub_stack);
> 4 lguest.c   create_thread   1048 vq->thread = clone(do_thread, stack +
> 32768, CLONE_VM |
>                                   SIGCHLD, vq);
>
> 3) insert some printk statement in those function
> 4) build and run, then watch the booting process output
> [root@localhost ~]# dmesg | grep 6436
> [    0.190000] run_helper_thread : clone success, pid = 6436
> [root@localhost ~]# dmesg | grep 6437
> [    0.190000] start_io_thread - clone success : pid = 6437
> [root@localhost ~]# dmesg | grep 6438
> [    0.190000] run_helper_thread : clone success, pid = 6438
>
> [real@real runuml]$ ps -ef | grep patch
> real     6423  1553  6 16:17 pts/0    00:00:02 ./linux_patched
> ubda=./Fedora20-x86-root_fs mem=256m
> real     6436  6423  0 16:17 pts/0    00:00:00 ./linux_patched
> ubda=./Fedora20-x86-root_fs mem=256m
> real     6437  6423  0 16:17 pts/0    00:00:00 ./linux_patched
> ubda=./Fedora20-x86-root_fs mem=256m
> real     6438  6423  0 16:17 pts/0    00:00:00 ./linux_patched
> ubda=./Fedora20-x86-root_fs mem=256m
> real     6439  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6459  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6479  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6492  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6565  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6567  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6572  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6573  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6576  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6605  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6619  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6621  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6707  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6715  6423  0 16:17 pts/0    00:00:00 [linux_patched]
> real     6765  6423  0 16:18 pts/0    00:00:00 [linux_patched]
>
> [root@localhost ~]# dmesg | grep proc
> [    0.090000] run_helper_thread : clone success, pid = 8387, proc=0806471d
> [    0.100000] run_helper_thread : clone success, pid = 8389, proc=080663a3
>
> [real@real linux-3.12.6]$ grep 0806471d System.map
> 0806471d t aio_thread
> [real@real linux-3.12.6]$ grep 080663a3 System.map
> 080663a3 t write_sigio_thread
>
> so, the four processes are:
> 1) uml kernel main thread
> 2) aio_thread
> 3) io_thread
> 4) write_sigio_thread
>
>
>
> On Fri, May 30, 2014 at 9:22 AM, Nalli, Sanketh <san...@hp...>
> wrote:
>
> Hi,
>
> So I start UML with the cmdline
>
> ./linux rootfstype=hostfs rw mem=1G init=/bin/bash
>
>
>
> When the bash shell comes up, I run my prog : ./my_prog
>
>
>
> 6173 pts/8    00:00:00 linux
>
> 6180 pts/8    00:00:00 linux
>
> 6181 pts/8    00:00:00 linux
>
> 6182 pts/8    00:00:00 linux
>
> 6183 pts/8    00:00:00 linux
>
> 6188 pts/8    00:00:13 linux
>
>
>
>
>
> The last item in the list with PID is 6188 is my program.
>
> I can tell because my_prog increments a counter in an infinite loop
>
> And consumes CPU cycles. It shows up on “top” as the dominant process.
>
>
>
> My question:
>
> 1.       /proc/6188/exe is invalid. Why ??
>
> I mean, it doesn’t point to anything.
>
> Shouldn’t it point to my_prog or something ?
>
>
>
> 2.       What do the 4 UML processes 6173, 6180, 6181, 6182 do ? (6183 is
> /bin/bash whos “exe” symlink is also doesn’t point to anything !!)
>
> 3.       When a UML process, say my_prog (PID 6188) makes a system call,
> where is the system call executed – is it within the addr space of 6173 (the
> UML kernel process) or 6188 (my_prog running in UML ??)
>
>
>
> -Sanketh
>
>
>
>
>
>
> ------------------------------------------------------------------------------
> Time is money. Stop wasting it! Get your web API in 5 minutes.
> www.restlet.com/download
> http://p.sf.net/sfu/restlet
> _______________________________________________
> User-mode-linux-user mailing list
> Use...@li...
> https://lists.sourceforge.net/lists/listinfo/user-mode-linux-user
>
>
>
>
> ------------------------------------------------------------------------------
> Learn Graph Databases - Download FREE O'Reilly Book
> "Graph Databases" is the definitive new guide to graph databases and their
> applications. Written by three acclaimed leaders in the field,
> this first edition is now available. Download your free book today!
> http://p.sf.net/sfu/NeoTech
> _______________________________________________
> User-mode-linux-user mailing list
> Use...@li...
> https://lists.sourceforge.net/lists/listinfo/user-mode-linux-user
>



-- 
Thanks,
//richard