From ca567df74a28a9fb368c6b2d93e864113f73f5c2 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Sun, 7 Jun 2020 22:47:08 +0200 Subject: nsfs: add pid translation ioctls Add ioctl()s to translate pids between pid namespaces. LXCFS is a tiny fuse filesystem used to virtualize various aspects of procfs. LXCFS is run on the host. The files and directories it creates can be bind-mounted by e.g. a container at startup and mounted over the various procfs files the container wishes to have virtualized. When e.g. a read request for uptime is received, LXCFS will receive the pid of the reader. In order to virtualize the corresponding read, LXCFS needs to know the pid of the init process of the reader's pid namespace. In order to do this, LXCFS first needs to fork() two helper processes. The first helper process setns() to the readers pid namespace. The second helper process is needed to create a process that is a proper member of the pid namespace. The second helper process then creates a ucred message with ucred.pid set to 1 and sends it back to LXCFS. The kernel will translate the ucred.pid field to the corresponding pid number in LXCFS's pid namespace. This way LXCFS can learn the init pid number of the reader's pid namespace and can go on to virtualize. Since these two forks() are costly LXCFS maintains an init pid cache that caches a given pid for a fixed amount of time. The cache is pruned during new read requests. However, even with the cache the hit of the two forks() is singificant when a very large number of containers are running. With this simple patch we add an ns ioctl that let's a caller retrieve the init pid nr of a pid namespace through its pid namespace fd. This significantly improves performance with a very simple change. Support translation of pids and tgids. Other concepts can be added but there are no obvious users for this right now. To protect against races pidfds can be used to check whether the process is still valid. If needed, this can also be extended to work on pidfds directly. Link: https://lore.kernel.org/r/20240619-work-ns_ioctl-v1-1-7c0097e6bb6b@kernel.org Reviewed-by: Alexander Mikhalitsyn Signed-off-by: Christian Brauner --- include/uapi/linux/nsfs.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'include') diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h index a0c8552b64ee..faeb9195da08 100644 --- a/include/uapi/linux/nsfs.h +++ b/include/uapi/linux/nsfs.h @@ -15,5 +15,13 @@ #define NS_GET_NSTYPE _IO(NSIO, 0x3) /* Get owner UID (in the caller's user namespace) for a user namespace */ #define NS_GET_OWNER_UID _IO(NSIO, 0x4) +/* Translate pid from target pid namespace into the caller's pid namespace. */ +#define NS_GET_PID_FROM_PIDNS _IOR(NSIO, 0x5, int) +/* Return thread-group leader id of pid in the callers pid namespace. */ +#define NS_GET_TGID_FROM_PIDNS _IOR(NSIO, 0x7, int) +/* Translate pid from caller's pid namespace into a target pid namespace. */ +#define NS_GET_PID_IN_PIDNS _IOR(NSIO, 0x6, int) +/* Return thread-group leader id of pid in the target pid namespace. */ +#define NS_GET_TGID_IN_PIDNS _IOR(NSIO, 0x8, int) #endif /* __LINUX_NSFS_H */ -- cgit v1.2.3-70-g09d2