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Subject[patch 2/4] proc: Show namespaces IDs in /proc/pid/ns/* files
This patch adds proc_ns_read method which provides
IDs for /proc/pid/ns/* files.

Based-on-patch-from: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
CC: Glauber Costa <glommer@parallels.com>
CC: Andi Kleen <andi@firstfloor.org>
CC: Tejun Heo <tj@kernel.org>
CC: Matt Helsley <matthltc@us.ibm.com>
CC: Pekka Enberg <penberg@kernel.org>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Vasiliy Kulikov <segoon@openwall.com>
CC: Andrew Morton <akpm@linux-foundation.org>
---
Documentation/filesystems/proc.txt | 24 ++++++++++++++++++++++++
fs/proc/namespaces.c | 21 +++++++++++++++++++++
include/linux/mm.h | 1 +
3 files changed, 46 insertions(+)

Index: linux-2.6.git/Documentation/filesystems/proc.txt
===================================================================
--- linux-2.6.git.orig/Documentation/filesystems/proc.txt
+++ linux-2.6.git/Documentation/filesystems/proc.txt
@@ -40,6 +40,7 @@ Table of Contents
3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
3.5 /proc/<pid>/mountinfo - Information about mounts
3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
+ 3.7 /proc/<pid>/ns - Information about namespaces


------------------------------------------------------------------------------
@@ -1545,3 +1546,26 @@ a task to set its own or one of its thre
is limited in size compared to the cmdline value, so writing anything longer
then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
comm value.
+
+3.7 /proc/<pid>/ns - Information about namespaces
+-----------------------------------------------------
+
+This directory consists of the following files "net", "uts", "ipc",
+and depend if appropriate CONFIG_ entry is set, i.e. it's possible
+to have only one, two or all three files here.
+
+Currently file contents provides that named "object id" number, which
+is a number useful for the one purpose only -- to test if two differen
+<pid> share the namespace.
+
+A typical format is
+
+id: 445332486300860161
+
+i.e. "id" followed by a number. One should never assume the number
+means something, it is only useful for "sameness" test with another number
+obtained from another <pid>.
+
+Moreover, a safe approach is to remember it as a string, since format may
+change in future and id would be not a long integer value, but something
+else, say SHA1/2 or even uuid encoded stream.
Index: linux-2.6.git/fs/proc/namespaces.c
===================================================================
--- linux-2.6.git.orig/fs/proc/namespaces.c
+++ linux-2.6.git/fs/proc/namespaces.c
@@ -27,10 +27,31 @@ static const struct proc_ns_operations *
#endif
};

+#ifdef CONFIG_GENERIC_OBJECT_IDS
+static ssize_t proc_ns_read(struct file *file, char __user *buf,
+ size_t len, loff_t *ppos)
+{
+ struct proc_inode *ei = PROC_I(file->f_dentry->d_inode);
+ char tmp[32];
+
+ snprintf(tmp, sizeof(tmp), "id:\t%lu\n",
+ gen_obj_id(ei->ns, GEN_OBJ_ID_NS));
+ return simple_read_from_buffer(buf, len, ppos, tmp, strlen(tmp));
+}
+
+static const struct file_operations ns_file_operations = {
+ .llseek = no_llseek,
+ .read = proc_ns_read,
+};
+
+#else
+
static const struct file_operations ns_file_operations = {
.llseek = no_llseek,
};

+#endif /* CONFIG_GENERIC_OBJECT_IDS */
+
static struct dentry *proc_ns_instantiate(struct inode *dir,
struct dentry *dentry, struct task_struct *task, const void *ptr)
{
Index: linux-2.6.git/include/linux/mm.h
===================================================================
--- linux-2.6.git.orig/include/linux/mm.h
+++ linux-2.6.git/include/linux/mm.h
@@ -1641,6 +1641,7 @@ extern void copy_user_huge_page(struct p
#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */

enum {
+ GEN_OBJ_ID_NS,
GEN_OBJ_ID_TYPES,
};



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