The patch titled
Subject: sysctl: add the kernel.ns_last_pid control
has been added to the -mm tree. Its filename is
sysctl-add-the-kernelns_last_pid-control.patch
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------------------------------------------------------
From: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Subject: sysctl: add the kernel.ns_last_pid control
The sysctl works on the current task's pid namespace, getting and setting
its last_pid field.
Writing is allowed for CAP_SYS_ADMIN-capable tasks thus making it possible
to create a task with desired pid value. This ability is required badly
for the checkpoint/restore in userspace.
This approach suits all the parties for now.
Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Serge Hallyn <serue@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/sysctl/kernel.txt | 8 +++++++
kernel/pid.c | 4 ++-
kernel/pid_namespace.c | 31 ++++++++++++++++++++++++++++++
3 files changed, 42 insertions(+), 1 deletion(-)
diff -puN Documentation/sysctl/kernel.txt~sysctl-add-the-kernelns_last_pid-control Documentation/sysctl/kernel.txt
--- a/Documentation/sysctl/kernel.txt~sysctl-add-the-kernelns_last_pid-control
+++ a/Documentation/sysctl/kernel.txt
@@ -401,6 +401,14 @@ PIDs of value pid_max or larger are not
==============================================================
+ns_last_pid:
+
+The last pid allocated in the current (the one task using this sysctl
+lives in) pid namespace. When selecting a pid for a next task on fork
+kernel tries to allocate a number starting from this one.
+
+==============================================================
+
powersave-nap: (PPC only)
If set, Linux-PPC will use the 'nap' mode of powersaving,
diff -puN kernel/pid.c~sysctl-add-the-kernelns_last_pid-control kernel/pid.c
--- a/kernel/pid.c~sysctl-add-the-kernelns_last_pid-control
+++ a/kernel/pid.c
@@ -137,7 +137,9 @@ static int pid_before(int base, int a, i
}
/*
- * We might be racing with someone else trying to set pid_ns->last_pid.
+ * We might be racing with someone else trying to set pid_ns->last_pid
+ * at the pid allocation time (there's also a sysctl for this, but racing
+ * with this one is OK, see comment in kernel/pid_namespace.c about it).
* We want the winner to have the "later" value, because if the
* "earlier" value prevails, then a pid may get reused immediately.
*
diff -puN kernel/pid_namespace.c~sysctl-add-the-kernelns_last_pid-control kernel/pid_namespace.c
--- a/kernel/pid_namespace.c~sysctl-add-the-kernelns_last_pid-control
+++ a/kernel/pid_namespace.c
@@ -191,9 +191,40 @@ void zap_pid_ns_processes(struct pid_nam
return;
}
+static int pid_ns_ctl_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct ctl_table tmp = *table;
+
+ if (write && !capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ /*
+ * Writing directly to ns' last_pid field is OK, since this field
+ * is volatile in a living namespace anyway and a code writing to
+ * it should synchronize its usage with external means.
+ */
+
+ tmp.data = ¤t->nsproxy->pid_ns->last_pid;
+ return proc_dointvec(&tmp, write, buffer, lenp, ppos);
+}
+
+static struct ctl_table pid_ns_ctl_table[] = {
+ {
+ .procname = "ns_last_pid",
+ .maxlen = sizeof(int),
+ .mode = 0666, /* permissions are checked in the handler */
+ .proc_handler = pid_ns_ctl_handler,
+ },
+ { }
+};
+
+static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
+
static __init int pid_namespaces_init(void)
{
pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
+ register_sysctl_paths(kern_path, pid_ns_ctl_table);
return 0;
}
_
Subject: Subject: sysctl: add the kernel.ns_last_pid control
Patches currently in -mm which might be from xemul@xxxxxxxxxxxxx are
procfs-make-proc_get_link-to-use-dentry-instead-of-inode.patch
procfs-introduce-the-proc-pid-map_files-directory.patch
sysctl-add-the-kernelns_last_pid-control.patch
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