This is a very timely reminder!
[Devel] [PATCH][DOCUMENTATION] The namespaces compatibility list doc
—————————- Original Message —————————-
Subject: [Devel] [PATCH][DOCUMENTATION] The namespaces compatibility list doc
From: “Pavel Emelyanov” <firstname.lastname@example.org>
Date: Fri, November 16, 2007 5:34 pm
To: “Andrew Morton” <email@example.com>
Cc: “Linux Containers” <firstname.lastname@example.org>
“Cedric Le Goater” <email@example.com>
“Theodore Tso” <firstname.lastname@example.org>
“Linux Kernel Mailing List” <email@example.com>
From time to time people begin discussions about how the namespaces are working/going-to-work together.
Ted T’so proposed to create some document that describes what problems user may have when he/she creates some new namespace, but keeps others shared. I liked this idea, so here’s the initial version of such a document with the problems I currently have in mind and can describe somewhat audibly – the “namespaces compatibility list”.
The Documentation/namespaces/ directory is about to contain more docs about the namespaces stuff.
Thanks to Cedirc for notes and spell checks on the doc.
Signed-off-by: Pavel Emelyanov <firstname.lastname@example.org>
Author: Pavel <email@example.com>
Date: Fri Nov 16 12:25:53 2007 +0300
Namespaces compatibility list
diff –git a/Documentation/00-INDEX b/Documentation/00-INDEX
index 910e511..3ead06b 100644
@@ -262,6 +262,8 @@ mtrr.txt
– how to use PPro Memory Type Range Registers to increase performance.
– info on the generic mutex subsystem.
+ – directory with various information about namespaces
– info on a TCP implementation of a network block device.
diff –git a/Documentation/namespaces/compatibility-list.txt b/Documentation/namespaces/compatibility-list.txt
new file mode 100644
@@ -0,0 +1,33 @@
+ Namespaces compatibility list
+This document contains the information about the problems user
+may have when creating tasks living in different namespaces.
+Here’s the summary. This matrix shows the known problems, that
+occur when tasks share some namespace (the columns) while living
+in different other namespaces (the rows):
+ UTS IPC VFS PID User Net
+IPC X 1
+PID 1 1 X
+User 2 X
+1. Both the IPC and the PID namespaces provide IDs to address
+ object inside the kernel. E.g. semaphore with ipcid or
+ process group with pid.
+ In both cases, tasks shouldn’t try exposing this id to some
+ other task living in a different namespace via a shared filesystem
+ or IPC shmem/message. The fact is that this ID is only valid
+ within the namespace it was obtained in and may refer to some
+ other object in another namespace.
+2. Intentionnaly, two equal user ids in different user namespaces
+ should not be equal from the VFS point of view. In other
+ words, user 10 in one user namespace shouldn’t have the same
+ access permissions to files, beloging to user 10 in another
+ namespace. But currently this is not so.
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