Hi, The linux kernel attaches a pid to newly forked process. I want to create a facility by which a process has the option of attaching a new pid to its child which is not in the pid space. Any suggestions of how this can be achieved? Nitin
On Sun, 20 Mar 2016 02:07:29 -0700, Nitin Varyani said:
The linux kernel attaches a pid to newly forked process. I want to create a facility by which a process has the option of attaching a new pid to its child which is not in the pid space.
Not at all sure what you mean by "not in the pid space", or what you're trying to achieve by doing it. But "pid namespaces" may be what you're looking for.
I am reframing my question: Sub-task 1: Until now, parent process cannot control the pid of the forked child. A pid gets assigned as a sequential number by the kernel at the time the process is forked . I want to modify kernel in such a way that parent process can control the pid of the forked child. Sub-task 2: On Linux, you can find the maximum PID value for your system with the following command: $ cat /proc/sys/kernel/pid_max Suppose pid_max=2000 for a system. I want that the parent process should be able to assign a pid which is greater that 2000 to the forked child. On Mon, Mar 21, 2016 at 12:03 AM, <Valdis.Kletnieks@vt.edu> wrote:
On Sun, 20 Mar 2016 02:07:29 -0700, Nitin Varyani said:
The linux kernel attaches a pid to newly forked process. I want to create a facility by which a process has the option of attaching a new
pid
to its child which is not in the pid space.
Not at all sure what you mean by "not in the pid space", or what you're trying to achieve by doing it.
But "pid namespaces" may be what you're looking for.
On Mon, 21 Mar 2016 10:33:44 +0530, Nitin Varyani said:
Sub-task 1: Until now, parent process cannot control the pid of the forked child. A pid gets assigned as a sequential number by the kernel at the time the process is forked . I want to modify kernel in such a way that parent process can control the pid of the forked child.
What does controlling the pid gain you? To what purpose?
Sub-task 2: On Linux, you can find the maximum PID value for your system with the following command:
$ cat /proc/sys/kernel/pid_max
Suppose pid_max=2000 for a system. I want that the parent process should be able to assign a pid which is greater that 2000 to the forked child.
Again, why would you want to do that? Anyhow... echo 3000 > /proc/sys/kernel/pid_max fork a process that gets a pid over 2000. Done. Note that on 32 bit systems, using a pid_max of over 32768 will cause various things in /proc to blow up. I suspect that you need to think harder about what problem you're actually trying to solve here - what will you do with a controlled child PID? Why does it even matter?
I am trying to create a distributed pid space. 0 to 2000 Computer 1 2001 to 4000 Computer 2 4001 to 6000 Computer 3 and so on... I am running a master user-level process at Computer 1 which sends a process context like code, data, registers, PC, etc as well as *"pid"* to slave processes running at other computers. The responsibility of the slave process is to fork a new process on order of master process and attach *"pid" *given by the master to the new process it has forked. Any system call on slave nodes will have an initial check of " Whether the process belongs to local node or to the master node?". That is, if kernel at Computer 2 pid of the process is 1500 On Mon, Mar 21, 2016 at 12:23 PM, <Valdis.Kletnieks@vt.edu> wrote:
On Mon, 21 Mar 2016 10:33:44 +0530, Nitin Varyani said:
Sub-task 1: Until now, parent process cannot control the pid of the forked child. A pid gets assigned as a sequential number by the kernel at the time the process is forked . I want to modify kernel in such a way that parent process can control the pid of the forked child.
What does controlling the pid gain you? To what purpose?
Sub-task 2: On Linux, you can find the maximum PID value for your system with the following command:
$ cat /proc/sys/kernel/pid_max
Suppose pid_max=2000 for a system. I want that the parent process should be able to assign a pid which is greater that 2000 to the forked child.
Again, why would you want to do that?
Anyhow...
echo 3000 > /proc/sys/kernel/pid_max fork a process that gets a pid over 2000.
Done.
Note that on 32 bit systems, using a pid_max of over 32768 will cause various things in /proc to blow up.
I suspect that you need to think harder about what problem you're actually trying to solve here - what will you do with a controlled child PID? Why does it even matter?
.....Continued.... That is, if kernel at Computer 2 finds that pid of a process requesting a system call is 1500, the request is forwarded to slave daemon which in turn contacts with the master daemon. Master daemon requests the kernel for the system call and sends the result back to slave daemon. On Mon, Mar 21, 2016 at 4:01 PM, Nitin Varyani <varyani.nitin1@gmail.com> wrote:
I am trying to create a distributed pid space.
0 to 2000 Computer 1 2001 to 4000 Computer 2 4001 to 6000 Computer 3
and so on...
I am running a master user-level process at Computer 1 which sends a process context like code, data, registers, PC, etc as well as *"pid"* to slave processes running at other computers. The responsibility of the slave process is to fork a new process on order of master process and attach *"pid" *given by the master to the new process it has forked. Any system call on slave nodes will have an initial check of " Whether the process belongs to local node or to the master node?". That is, if kernel at Computer 2 pid of the process is 1500
On Mon, Mar 21, 2016 at 12:23 PM, <Valdis.Kletnieks@vt.edu> wrote:
On Mon, 21 Mar 2016 10:33:44 +0530, Nitin Varyani said:
Sub-task 1: Until now, parent process cannot control the pid of the forked child. A pid gets assigned as a sequential number by the kernel at the time the process is forked . I want to modify kernel in such a way that parent process can control the pid of the forked child.
What does controlling the pid gain you? To what purpose?
Sub-task 2: On Linux, you can find the maximum PID value for your system with the following command:
$ cat /proc/sys/kernel/pid_max
Suppose pid_max=2000 for a system. I want that the parent process should be able to assign a pid which is greater that 2000 to the forked child.
Again, why would you want to do that?
Anyhow...
echo 3000 > /proc/sys/kernel/pid_max fork a process that gets a pid over 2000.
Done.
Note that on 32 bit systems, using a pid_max of over 32768 will cause various things in /proc to blow up.
I suspect that you need to think harder about what problem you're actually trying to solve here - what will you do with a controlled child PID? Why does it even matter?
A representative process, that is, a process without any user stack, register values, PC, etc, with *"pid" *is maintained at the master node. Now, the process which was migrated to a remote node, in this example Computer 2, and having process id *"pid", *decides to fork(). It is a system call and is forwarded in the same way to master process. This request is forwarded to the representative process with process id *"pid"*. The representative process forks() leading to a new representative process with process id *"cpid". *This "cpid" is forwarded to master process which forwards it to slave process. The slave process forwards *"cpid"* to the remote process with process id *"pid"*. The remote process with process id *"pid"* now forks a child and attaches *"cpid" * to its child. This is overview of what I want to achieve. A small correction in my last mail. .....Continued.... That is, if kernel at Computer 2 finds that pid of a process requesting a system call is 1500, the request is forwarded to slave daemon which in turn contacts with the master daemon. Master daemon forwards this information to corresponding representative process which requests the kernel for the system call and sends the result back to slave daemon. On Mon, Mar 21, 2016 at 4:03 PM, Nitin Varyani <varyani.nitin1@gmail.com> wrote:
.....Continued.... That is, if kernel at Computer 2 finds that pid of a process requesting a system call is 1500, the request is forwarded to slave daemon which in turn contacts with the master daemon. Master daemon requests the kernel for the system call and sends the result back to slave daemon.
On Mon, Mar 21, 2016 at 4:01 PM, Nitin Varyani <varyani.nitin1@gmail.com> wrote:
I am trying to create a distributed pid space.
0 to 2000 Computer 1 2001 to 4000 Computer 2 4001 to 6000 Computer 3
and so on...
I am running a master user-level process at Computer 1 which sends a process context like code, data, registers, PC, etc as well as *"pid"* to slave processes running at other computers. The responsibility of the slave process is to fork a new process on order of master process and attach *"pid" *given by the master to the new process it has forked. Any system call on slave nodes will have an initial check of " Whether the process belongs to local node or to the master node?". That is, if kernel at Computer 2 pid of the process is 1500
On Mon, Mar 21, 2016 at 12:23 PM, <Valdis.Kletnieks@vt.edu> wrote:
On Mon, 21 Mar 2016 10:33:44 +0530, Nitin Varyani said:
Sub-task 1: Until now, parent process cannot control the pid of the forked child. A pid gets assigned as a sequential number by the kernel at the time the process is forked . I want to modify kernel in such a way that parent process can control the pid of the forked child.
What does controlling the pid gain you? To what purpose?
Sub-task 2: On Linux, you can find the maximum PID value for your system with the following command:
$ cat /proc/sys/kernel/pid_max
Suppose pid_max=2000 for a system. I want that the parent process should be able to assign a pid which is greater that 2000 to the forked child.
Again, why would you want to do that?
Anyhow...
echo 3000 > /proc/sys/kernel/pid_max fork a process that gets a pid over 2000.
Done.
Note that on 32 bit systems, using a pid_max of over 32768 will cause various things in /proc to blow up.
I suspect that you need to think harder about what problem you're actually trying to solve here - what will you do with a controlled child PID? Why does it even matter?
On Mon, 21 Mar 2016 16:01:41 +0530, Nitin Varyani said:
I am running a master user-level process at Computer 1 which sends a process context like code, data, registers, PC, etc as well as *"pid"* to slave processes running at other computers. The responsibility of the slave process is to fork a new process on order of master process and attach *"pid" *given by the master to the new process it has forked. Any system call on slave nodes will have an initial check of " Whether the process belongs to local node or to the master node?". That is, if kernel at Computer 2 pid of the process is 1500
None of that requires actually controlling the PID of the child. Consider this code: int child_pid[5], j; pid_t child; for (j=0;j<5;j++) { child = fork(); if (child == 0) go_init_worker_process(); else child_pid[j] = child; } Now you have 5 children, and know what process IDs they are, without having to do any kernel hacking at all. This has been a long-understood idiom in the Unix/Linux world - I remember first seeing it on SunOS 3.2 back in 1985 or so...
On Die, 2016-03-22 at 01:26 -0400, Valdis.Kletnieks@vt.edu wrote:
On Mon, 21 Mar 2016 16:01:41 +0530, Nitin Varyani said:
I am running a master user-level process at Computer 1 which sends a process context like code, data, registers, PC, etc as well as *"pid"* to slave processes running at other computers. The responsibility of the slave process is to fork a new process on order of master process and attach *"pid" *given by the master to the new process it has forked. Any system call on slave nodes will have an initial check of " Whether the process belongs to local node or to the master node?". That is, if kernel at Computer 2 pid of the process is 1500
None of that requires actually controlling the PID of the child.
Well, I think that the OP wants to map the PIDs with a fixed offset per host. So e.g. the local PID == 14 becomes 20014 on all other nodes. At least for debugging it's easier than some random mappings;-) As for top post: TTBOMK there is no SysCall for doing that. * Perhaps one can achieve something similar with containers - one container per remote host or so (but I never used containers actively myself) or (ab)use KVM (does vServer still live?) for local "pseudo-VMs" (and use there the original PIDs - or so). * The manual page of clone(2) doesn't reveal to me if it's possible to wish for a PID. * You could clone (pun not intended;-) the fork() syscall and add an parameter - the PID - to it (and e.g. return -1 if it's already used). BTW I don't know how the rest of the kernel reacts to such artifical PIDs (but you will see;-) outside the "official range". MfG, Bernd -- "What happens when you read some doc and either it doesn't answer your question or is demonstrably wrong? In Linux, you say "Linux sucks" and go read the code. In Windows/Oracle/etc you say "Windows sucks" and start banging your head against the wall." - Denis Vlasenko on lkml
If I do the following thing: struct pid remote_struct_pid; remote_struct_pid.numbers[0].nr=*my_pid*; p = copy_process(clone_flags, stack_start, stack_size, child_tidptr, *remote_struct_pid*, trace, tls); and modify the copy_process function little bit (marked in BOLD), it may serve my objective. if (pid != &init_struct_pid *&& pid == NULL*) { retval = -ENOMEM; pid = alloc_pid(p->nsproxy->pid_ns); if (!pid) goto bad_fork_cleanup_io; } p->pid = pid_nr(pid); The pids by kernel are allocated in the range (RESERVED_PIDS, PID_MAX_DEFAULT) and I will choose *my_pid* outside this range. I will have to modify system calls/kernel to cater to such processes. On Tue, Mar 22, 2016 at 3:55 PM, Bernd Petrovitsch < bernd@petrovitsch.priv.at> wrote:
On Die, 2016-03-22 at 01:26 -0400, Valdis.Kletnieks@vt.edu wrote:
On Mon, 21 Mar 2016 16:01:41 +0530, Nitin Varyani said:
I am running a master user-level process at Computer 1 which sends a process context like code, data, registers, PC, etc as well as *"pid"* to slave processes running at other computers. The responsibility of the slave process is to fork a new process on order of master process and attach *"pid" *given by the master to the new process it has forked. Any system call on slave nodes will have an initial check of " Whether the process belongs to local node or to the master node?". That is, if kernel at Computer 2 pid of the process is 1500
None of that requires actually controlling the PID of the child.
Well, I think that the OP wants to map the PIDs with a fixed offset per host. So e.g. the local PID == 14 becomes 20014 on all other nodes. At least for debugging it's easier than some random mappings;-)
As for top post: TTBOMK there is no SysCall for doing that. * Perhaps one can achieve something similar with containers - one container per remote host or so (but I never used containers actively myself) or (ab)use KVM (does vServer still live?) for local "pseudo-VMs" (and use there the original PIDs - or so). * The manual page of clone(2) doesn't reveal to me if it's possible to wish for a PID. * You could clone (pun not intended;-) the fork() syscall and add an parameter - the PID - to it (and e.g. return -1 if it's already used).
BTW I don't know how the rest of the kernel reacts to such artifical PIDs (but you will see;-) outside the "official range".
MfG, Bernd -- "What happens when you read some doc and either it doesn't answer your question or is demonstrably wrong? In Linux, you say "Linux sucks" and go read the code. In Windows/Oracle/etc you say "Windows sucks" and start banging your head against the wall." - Denis Vlasenko on lkml
rather this will also suffice if (* pid == NULL*) { retval = -ENOMEM; pid = alloc_pid(p->nsproxy->pid_ns); if (!pid) goto bad_fork_cleanup_io; } p->pid = pid_nr(pid); On Sun, Mar 27, 2016 at 4:57 PM, Nitin Varyani <varyani.nitin1@gmail.com> wrote:
If I do the following thing:
struct pid remote_struct_pid; remote_struct_pid.numbers[0].nr=*my_pid*; p = copy_process(clone_flags, stack_start, stack_size, child_tidptr, *remote_struct_pid*, trace, tls);
and modify the copy_process function little bit (marked in BOLD), it may serve my objective.
if (pid != &init_struct_pid *&& pid == NULL*) { retval = -ENOMEM; pid = alloc_pid(p->nsproxy->pid_ns); if (!pid) goto bad_fork_cleanup_io; }
p->pid = pid_nr(pid);
The pids by kernel are allocated in the range (RESERVED_PIDS, PID_MAX_DEFAULT) and I will choose *my_pid* outside this range. I will have to modify system calls/kernel to cater to such processes.
On Tue, Mar 22, 2016 at 3:55 PM, Bernd Petrovitsch < bernd@petrovitsch.priv.at> wrote:
On Die, 2016-03-22 at 01:26 -0400, Valdis.Kletnieks@vt.edu wrote:
On Mon, 21 Mar 2016 16:01:41 +0530, Nitin Varyani said:
I am running a master user-level process at Computer 1 which sends a process context like code, data, registers, PC, etc as well as *"pid"* to slave processes running at other computers. The responsibility of the slave process is to fork a new process on order of master process and attach *"pid" *given by the master to the new process it has forked. Any system call on slave nodes will have an initial check of " Whether the process belongs to local node or to the master node?". That is, if kernel at Computer 2 pid of the process is 1500
None of that requires actually controlling the PID of the child.
Well, I think that the OP wants to map the PIDs with a fixed offset per host. So e.g. the local PID == 14 becomes 20014 on all other nodes. At least for debugging it's easier than some random mappings;-)
As for top post: TTBOMK there is no SysCall for doing that. * Perhaps one can achieve something similar with containers - one container per remote host or so (but I never used containers actively myself) or (ab)use KVM (does vServer still live?) for local "pseudo-VMs" (and use there the original PIDs - or so). * The manual page of clone(2) doesn't reveal to me if it's possible to wish for a PID. * You could clone (pun not intended;-) the fork() syscall and add an parameter - the PID - to it (and e.g. return -1 if it's already used).
BTW I don't know how the rest of the kernel reacts to such artifical PIDs (but you will see;-) outside the "official range".
MfG, Bernd -- "What happens when you read some doc and either it doesn't answer your question or is demonstrably wrong? In Linux, you say "Linux sucks" and go read the code. In Windows/Oracle/etc you say "Windows sucks" and start banging your head against the wall." - Denis Vlasenko on lkml
On Sun, Mar 20, 2016 at 02:07:29AM -0700, Nitin Varyani wrote:
Hi, The linux kernel attaches a pid to newly forked process. I want to create a facility by which a process has the option of attaching a new pid to its child which is not in the pid space. Any suggestions of how this can be achieved? Nitin
Don't know what you are trying to accomplish, but have a look at this: https://criu.org/Pid_restore
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participants (4)
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Nitin Varyani -
Valdis.Kletnieks＠vt.edu