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Message-ID: <87fvj3ngv0.fsf@x220.int.ebiederm.org>
Date: Tue, 17 Jun 2014 18:31:15 -0700
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Chen Hanxiao <chenhanxiao@...fujitsu.com>
Cc: <containers@...ts.linux-foundation.org>,
<linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Serge Hallyn <serge.hallyn@...ntu.com>,
"Daniel P. Berrange" <berrange@...hat.com>,
Oleg Nesterov <oleg@...hat.com>,
Al Viro <viro@...iv.linux.org.uk>,
David Howells <dhowells@...hat.com>,
Richard Weinberger <richard.weinberger@...il.com>,
Pavel Emelyanov <xemul@...allels.com>,
Vasiliy Kulikov <segooon@...il.com>,
Gotou Yasunori <y-goto@...fujitsu.com>,
Linux API <linux-api@...r.kernel.org>,
Michael Kerrisk-manpages <mtk.manpages@...il.com>
Subject: Re: [PATCH] ns: introduce getnspid syscall
Chen Hanxiao <chenhanxiao@...fujitsu.com> writes:
> We need a direct method of getting the pid inside containers.
> If some issues occurred inside container guest, host user
> could not know which process is in trouble just by guest pid:
> the users of container guest only knew the pid inside containers.
> This will bring obstacle for trouble shooting.
There is also some ongoing work to export this information via a proc
file which seems more appropriate for solving your problem. Certainly
for debugging something easily human discoverable is needed.
> int getnspid(pid_t pid, int fd1, int fd2, int pidtype);
The pidtype is nonsense. The translation of a pid does not depend upon
type. Using that kind of nonsense will lead you and others into confusion.
> pid: the pid number need to be translated.
>
> fd: a file descriptor referring to one of
> the namespace entries in a /proc/[pid]/ns/pid.
> fd1 for destination ns(ns1), where the pid came from.
> fd2 for reference ns(ns2), while fd2 = -2 means for current ns.
>
> pidtype: 0 PIDTYPE_PID; 1 PIDTYPE_PGID; 2 PIDTYPE_SID.
>
> return value:
> >0: translated pid in ns1(fd1) seen from ns2(fd2).
> <0: on failure.
Elsewhere we use 0 on pid translation failure. Why be different here?
Eric
> Signed-off-by: Chen Hanxiao <chenhanxiao@...fujitsu.com>
> ---
> arch/x86/syscalls/syscall_32.tbl | 1 +
> arch/x86/syscalls/syscall_64.tbl | 1 +
> include/linux/syscalls.h | 1 +
> kernel/nsproxy.c | 60 ++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 63 insertions(+)
>
> diff --git a/arch/x86/syscalls/syscall_32.tbl b/arch/x86/syscalls/syscall_32.tbl
> index d6b8679..9de0b32 100644
> --- a/arch/x86/syscalls/syscall_32.tbl
> +++ b/arch/x86/syscalls/syscall_32.tbl
> @@ -360,3 +360,4 @@
> 351 i386 sched_setattr sys_sched_setattr
> 352 i386 sched_getattr sys_sched_getattr
> 353 i386 renameat2 sys_renameat2
> +354 i386 getnspid sys_getnspid
> diff --git a/arch/x86/syscalls/syscall_64.tbl b/arch/x86/syscalls/syscall_64.tbl
> index ec255a1..1630a8a 100644
> --- a/arch/x86/syscalls/syscall_64.tbl
> +++ b/arch/x86/syscalls/syscall_64.tbl
> @@ -323,6 +323,7 @@
> 314 common sched_setattr sys_sched_setattr
> 315 common sched_getattr sys_sched_getattr
> 316 common renameat2 sys_renameat2
> +317 common getnspid sys_getnspid
>
> #
> # x32-specific system call numbers start at 512 to avoid cache impact
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index b0881a0..271c7b1 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -866,4 +866,5 @@ asmlinkage long sys_process_vm_writev(pid_t pid,
> asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type,
> unsigned long idx1, unsigned long idx2);
> asmlinkage long sys_finit_module(int fd, const char __user *uargs, int flags);
> +asmlinkage long sys_getpidns(pid_t pid, int fd1, int fd2, int pidtype);
> #endif
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index 8e78110..3eda90a 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -261,6 +261,66 @@ out:
> return err;
> }
>
> +SYSCALL_DEFINE4(getnspid, pid_t, pid, int, fd1, int, fd2, int, pidtype)
> +{
> + struct file *file1 = NULL, *file2 = NULL;
> + struct task_struct *task;
> + struct pid_namespace *ns1, *ns2;
> + struct proc_ns *ei;
> + int ret = -1;
> +
> + if (pidtype >= PIDTYPE_MAX)
> + return -EINVAL;
> +
> + file1 = proc_ns_fget(fd1);
> + if (IS_ERR(file1))
> + return PTR_ERR(file1);
> + ei = get_proc_ns(file_inode(file1));
> + ns1 = (struct pid_namespace *)ei->ns;
> +
> + /* fd == -2 for current pid ns */
> + if (fd2 == -2) {
> + ns2 = task_active_pid_ns(current);
> + } else {
> + file2 = proc_ns_fget(fd2);
> + if (IS_ERR(file2)) {
> + fput(file1);
> + return PTR_ERR(file2);
> + }
> + ei = get_proc_ns(file_inode(file2));
> + ns2 = (struct pid_namespace *)ei->ns;
> + }
> +
> + rcu_read_lock();
> + task = find_task_by_pid_ns(pid, ns1);
The functions you want to be using here are:
find_pid_ns and pid_nr_ns.
> + rcu_read_unlock();
> + if (!task) {
> + ret = -ESRCH;
> + goto out;
> + }
> +
> + switch (pidtype) {
> + case PIDTYPE_PID:
> + ret = task_pid_nr_ns(task, ns2);
> + break;
> + case PIDTYPE_PGID:
> + ret = task_pgrp_nr_ns(task, ns2);
> + break;
> + case PIDTYPE_SID:
> + ret = task_session_nr_ns(task, ns2);
> + break;
> + default:
> + ret = -EINVAL;
> + }
> + ret = (ret == 0) ? -ESRCH : ret;
> +
> +out:
> + fput(file1);
> + if (file2)
> + fput(file2);
> + return ret;
> +}
> +
> int __init nsproxy_cache_init(void)
> {
> nsproxy_cachep = KMEM_CACHE(nsproxy, SLAB_PANIC);
--
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