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Message-Id: <1274460848-11377-26-git-send-email-gregkh@suse.de> Date: Fri, 21 May 2010 09:53:56 -0700 From: Greg Kroah-Hartman <gregkh@...e.de> To: linux-kernel@...r.kernel.org Cc: "Serge E. Hallyn" <serue@...ibm.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Tejun Heo <tj@...nel.org>, Greg Kroah-Hartman <gregkh@...e.de> Subject: [PATCH 26/38] sysfs-namespaces: add a high-level Documentation file From: Serge E. Hallyn <serue@...ibm.com> The first three paragraphs are almost verbatim taken from Eric's commit message on the patch introducing network ns tags. The next two paragraphs I wrote to be a brief high level overview. The last section is taken from the commit message on "Implement sysfs tagged directory support", but updated. Hopefully correctly. Signed-off-by: Serge E. Hallyn <serue@...ibm.com> Cc: Eric W. Biederman <ebiederm@...ssion.com> Cc: Tejun Heo <tj@...nel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de> --- Documentation/filesystems/sysfs-tagging.txt | 42 +++++++++++++++++++++++++++ 1 files changed, 42 insertions(+), 0 deletions(-) create mode 100644 Documentation/filesystems/sysfs-tagging.txt diff --git a/Documentation/filesystems/sysfs-tagging.txt b/Documentation/filesystems/sysfs-tagging.txt new file mode 100644 index 0000000..caaaf12 --- /dev/null +++ b/Documentation/filesystems/sysfs-tagging.txt @@ -0,0 +1,42 @@ +Sysfs tagging +------------- + +(Taken almost verbatim from Eric Biederman's netns tagging patch +commit msg) + +The problem. Network devices show up in sysfs and with the network +namespace active multiple devices with the same name can show up in +the same directory, ouch! + +To avoid that problem and allow existing applications in network +namespaces to see the same interface that is currently presented in +sysfs, sysfs now has tagging directory support. + +By using the network namespace pointers as tags to separate out the +the sysfs directory entries we ensure that we don't have conflicts +in the directories and applications only see a limited set of +the network devices. + +Each sysfs directory entry may be tagged with zero or one +namespaces. A sysfs_dirent is augmented with a void *s_ns. If a +directory entry is tagged, then sysfs_dirent->s_flags will have a +flag between KOBJ_NS_TYPE_NONE and KOBJ_NS_TYPES, and s_ns will +point to the namespace to which it belongs. + +Each sysfs superblock's sysfs_super_info contains an array void +*ns[KOBJ_NS_TYPES]. When a a task in a tagging namespace +kobj_nstype first mounts sysfs, a new superblock is created. It +will be differentiated from other sysfs mounts by having its +s_fs_info->ns[kobj_nstype] set to the new namespace. Note that +through bind mounting and mounts propagation, a task can easily view +the contents of other namespaces' sysfs mounts. Therefore, when a +namespace exits, it will call kobj_ns_exit() to invalidate any +sysfs_dirent->s_ns pointers pointing to it. + +Users of this interface: +- define a type in the kobj_ns_type enumeration. +- call kobj_ns_type_register() with its kobj_ns_type_operations which has + - current_ns() which returns current's namespace + - netlink_ns() which returns a socket's namespace + - initial_ns() which returns the initial namesapce +- call kobj_ns_exit() when an individual tag is no longer valid -- 1.7.0.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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