[PATCH v3] SUNRPC: set desired file system root before connecting local transports

[PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Stanislav Kinsbursky]

Today, there is a problem in connecting of local SUNRPC thansports. These
transports uses UNIX sockets and connection itself is done by rpciod
workqueue.
But all local transports are connecting in rpciod context. I.e. UNIX sockets
lookup is done in context of process file system root.
This works nice until we will try to mount NFS from process with other root -
for example in container. This container can have it's own (nested) root and
rcpbind process, listening on it's own unix sockets. But NFS mount attempt in
this container will register new service (Lockd for example) in global rpcbind
- not containers's one.
This patch solves the problem by switching rpciod kernel thread's file system
root to the right one (stored on transport) while connecting of local
transports.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
---
 net/sunrpc/xprtsock.c |   52 +++++++++++++++++++++++++++++++++++++++++++++++--
 1 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index aaaadfb..ecbced1 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -37,6 +37,7 @@
 #include <linux/sunrpc/svcsock.h>
 #include <linux/sunrpc/xprtsock.h>
 #include <linux/file.h>
+#include <linux/fs_struct.h>
 #ifdef CONFIG_SUNRPC_BACKCHANNEL
 #include <linux/sunrpc/bc_xprt.h>
 #endif
@@ -255,6 +256,11 @@ struct sock_xprt {
 	void			(*old_state_change)(struct sock *);
 	void			(*old_write_space)(struct sock *);
 	void			(*old_error_report)(struct sock *);
+
+	/*
+	 * Saved transport creator root. Required for local transports only.
+	 */
+	struct path		root;
 };
 
 /*
@@ -1876,6 +1882,30 @@ static int xs_local_finish_connecting(struct rpc_xprt *xprt,
 	return kernel_connect(sock, xs_addr(xprt), xprt->addrlen, 0);
 }
 
+/*
+ * __xs_local_swap_root - swap current root to tranport's root helper.
+ * @new_root - path to set to current fs->root.
+ * @old_root - optinal paoinet to save current root to
+ *
+ * This routine is requieed to connecting unix sockets to absolute path in
+ * proper root environment.
+ * Note: no path_get() will be called. I.e. caller have to hold reference to
+ * new_root.
+ */
+static void __xs_local_swap_root(struct path *new_root, struct path *old_root)
+{
+	struct fs_struct *fs = current->fs;
+
+	spin_lock(&fs->lock);
+	write_seqcount_begin(&fs->seq);
+	if (old_root)
+		*old_root = fs->root;
+	fs->root = *new_root;
+	write_seqcount_end(&fs->seq);
+	spin_unlock(&fs->lock);
+}
+
+
 /**
  * xs_local_setup_socket - create AF_LOCAL socket, connect to a local endpoint
  * @xprt: RPC transport to connect
@@ -1891,6 +1921,7 @@ static void xs_local_setup_socket(struct work_struct *work)
 	struct rpc_xprt *xprt = &transport->xprt;
 	struct socket *sock;
 	int status = -EIO;
+	struct path root;
 
 	current->flags |= PF_FSTRANS;
 
@@ -1907,7 +1938,10 @@ static void xs_local_setup_socket(struct work_struct *work)
 	dprintk("RPC:       worker connecting xprt %p via AF_LOCAL to %s\n",
 			xprt, xprt->address_strings[RPC_DISPLAY_ADDR]);
 
+	__xs_local_swap_root(&transport->root, &root);
 	status = xs_local_finish_connecting(xprt, sock);
+	__xs_local_swap_root(&root, NULL);
+
 	switch (status) {
 	case 0:
 		dprintk("RPC:       xprt %p connected to %s\n",
@@ -2256,6 +2290,18 @@ static void xs_connect(struct rpc_task *task)
 	}
 }
 
+static void xs_local_destroy(struct rpc_xprt *xprt)
+{
+	struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt);
+	struct path root = transport->root;
+
+	dprintk("RPC:       xs_local_destroy xprt %p\n", xprt);
+
+	xs_destroy(xprt);
+
+	path_put(&root);
+}
+
 /**
  * xs_local_print_stats - display AF_LOCAL socket-specifc stats
  * @xprt: rpc_xprt struct containing statistics
@@ -2475,7 +2521,7 @@ static struct rpc_xprt_ops xs_local_ops = {
 	.send_request		= xs_local_send_request,
 	.set_retrans_timeout	= xprt_set_retrans_timeout_def,
 	.close			= xs_close,
-	.destroy		= xs_destroy,
+	.destroy		= xs_local_destroy,
 	.print_stats		= xs_local_print_stats,
 };
 
@@ -2654,8 +2700,10 @@ static struct rpc_xprt *xs_setup_local(struct xprt_create *args)
 	dprintk("RPC:       set up xprt to %s via AF_LOCAL\n",
 			xprt->address_strings[RPC_DISPLAY_ADDR]);
 
-	if (try_module_get(THIS_MODULE))
+	if (try_module_get(THIS_MODULE)) {
+		get_fs_root(current->fs, &transport->root);
 		return xprt;
+	}
 	ret = ERR_PTR(-EINVAL);
 out_err:
 	xprt_free(xprt);

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

Cc'ing Eric since I seem to recall he suggested doing it this way?

Seems OK to me, but maybe that swap_root should be in common code?  (Or
maybe we could use set_fs_root()?)

I'm assuming it's up to Trond to take this.--b.

On Mon, Oct 08, 2012 at 02:56:32PM +0400, Stanislav Kinsbursky wrote:
> Today, there is a problem in connecting of local SUNRPC thansports. These
> transports uses UNIX sockets and connection itself is done by rpciod
> workqueue.
> But all local transports are connecting in rpciod context. I.e. UNIX sockets
> lookup is done in context of process file system root.
> This works nice until we will try to mount NFS from process with other root -
> for example in container. This container can have it's own (nested) root and
> rcpbind process, listening on it's own unix sockets. But NFS mount attempt in
> this container will register new service (Lockd for example) in global rpcbind
> - not containers's one.
> This patch solves the problem by switching rpciod kernel thread's file system
> root to the right one (stored on transport) while connecting of local
> transports.
> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
> ---
>  net/sunrpc/xprtsock.c |   52 +++++++++++++++++++++++++++++++++++++++++++++++--
>  1 files changed, 50 insertions(+), 2 deletions(-)
> 
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index aaaadfb..ecbced1 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -37,6 +37,7 @@
>  #include <linux/sunrpc/svcsock.h>
>  #include <linux/sunrpc/xprtsock.h>
>  #include <linux/file.h>
> +#include <linux/fs_struct.h>
>  #ifdef CONFIG_SUNRPC_BACKCHANNEL
>  #include <linux/sunrpc/bc_xprt.h>
>  #endif
> @@ -255,6 +256,11 @@ struct sock_xprt {
>  	void			(*old_state_change)(struct sock *);
>  	void			(*old_write_space)(struct sock *);
>  	void			(*old_error_report)(struct sock *);
> +
> +	/*
> +	 * Saved transport creator root. Required for local transports only.
> +	 */
> +	struct path		root;
>  };
>  
>  /*
> @@ -1876,6 +1882,30 @@ static int xs_local_finish_connecting(struct rpc_xprt *xprt,
>  	return kernel_connect(sock, xs_addr(xprt), xprt->addrlen, 0);
>  }
>  
> +/*
> + * __xs_local_swap_root - swap current root to tranport's root helper.
> + * @new_root - path to set to current fs->root.
> + * @old_root - optinal paoinet to save current root to
> + *
> + * This routine is requieed to connecting unix sockets to absolute path in
> + * proper root environment.
> + * Note: no path_get() will be called. I.e. caller have to hold reference to
> + * new_root.
> + */
> +static void __xs_local_swap_root(struct path *new_root, struct path *old_root)
> +{
> +	struct fs_struct *fs = current->fs;
> +
> +	spin_lock(&fs->lock);
> +	write_seqcount_begin(&fs->seq);
> +	if (old_root)
> +		*old_root = fs->root;
> +	fs->root = *new_root;
> +	write_seqcount_end(&fs->seq);
> +	spin_unlock(&fs->lock);
> +}
> +
> +
>  /**
>   * xs_local_setup_socket - create AF_LOCAL socket, connect to a local endpoint
>   * @xprt: RPC transport to connect
> @@ -1891,6 +1921,7 @@ static void xs_local_setup_socket(struct work_struct *work)
>  	struct rpc_xprt *xprt = &transport->xprt;
>  	struct socket *sock;
>  	int status = -EIO;
> +	struct path root;
>  
>  	current->flags |= PF_FSTRANS;
>  
> @@ -1907,7 +1938,10 @@ static void xs_local_setup_socket(struct work_struct *work)
>  	dprintk("RPC:       worker connecting xprt %p via AF_LOCAL to %s\n",
>  			xprt, xprt->address_strings[RPC_DISPLAY_ADDR]);
>  
> +	__xs_local_swap_root(&transport->root, &root);
>  	status = xs_local_finish_connecting(xprt, sock);
> +	__xs_local_swap_root(&root, NULL);
> +
>  	switch (status) {
>  	case 0:
>  		dprintk("RPC:       xprt %p connected to %s\n",
> @@ -2256,6 +2290,18 @@ static void xs_connect(struct rpc_task *task)
>  	}
>  }
>  
> +static void xs_local_destroy(struct rpc_xprt *xprt)
> +{
> +	struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt);
> +	struct path root = transport->root;
> +
> +	dprintk("RPC:       xs_local_destroy xprt %p\n", xprt);
> +
> +	xs_destroy(xprt);
> +
> +	path_put(&root);
> +}
> +
>  /**
>   * xs_local_print_stats - display AF_LOCAL socket-specifc stats
>   * @xprt: rpc_xprt struct containing statistics
> @@ -2475,7 +2521,7 @@ static struct rpc_xprt_ops xs_local_ops = {
>  	.send_request		= xs_local_send_request,
>  	.set_retrans_timeout	= xprt_set_retrans_timeout_def,
>  	.close			= xs_close,
> -	.destroy		= xs_destroy,
> +	.destroy		= xs_local_destroy,
>  	.print_stats		= xs_local_print_stats,
>  };
>  
> @@ -2654,8 +2700,10 @@ static struct rpc_xprt *xs_setup_local(struct xprt_create *args)
>  	dprintk("RPC:       set up xprt to %s via AF_LOCAL\n",
>  			xprt->address_strings[RPC_DISPLAY_ADDR]);
>  
> -	if (try_module_get(THIS_MODULE))
> +	if (try_module_get(THIS_MODULE)) {
> +		get_fs_root(current->fs, &transport->root);
>  		return xprt;
> +	}
>  	ret = ERR_PTR(-EINVAL);
>  out_err:
>  	xprt_free(xprt);
> 

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Myklebust, Trond]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 5942 bytes --]

On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
> Cc'ing Eric since I seem to recall he suggested doing it this way?
> 
> Seems OK to me, but maybe that swap_root should be in common code?  (Or
> maybe we could use set_fs_root()?)
> 
> I'm assuming it's up to Trond to take this.--b.

I'm reluctant to do that at this time since the original proposal was
precisely that of export set_fs_root() and using it around the AF_LOCAL
socket bind. That proposal was NACKed by Al Viro.

If Al is OK with the idea of us creating a private version of
set_fs_root, then I'd like to see an official Acked-by: that we can
append to this commit.

Cheers
  Trond

> On Mon, Oct 08, 2012 at 02:56:32PM +0400, Stanislav Kinsbursky wrote:
> > Today, there is a problem in connecting of local SUNRPC thansports. These
> > transports uses UNIX sockets and connection itself is done by rpciod
> > workqueue.
> > But all local transports are connecting in rpciod context. I.e. UNIX sockets
> > lookup is done in context of process file system root.
> > This works nice until we will try to mount NFS from process with other root -
> > for example in container. This container can have it's own (nested) root and
> > rcpbind process, listening on it's own unix sockets. But NFS mount attempt in
> > this container will register new service (Lockd for example) in global rpcbind
> > - not containers's one.
> > This patch solves the problem by switching rpciod kernel thread's file system
> > root to the right one (stored on transport) while connecting of local
> > transports.
> > 
> > Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
> > ---
> >  net/sunrpc/xprtsock.c |   52 +++++++++++++++++++++++++++++++++++++++++++++++--
> >  1 files changed, 50 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > index aaaadfb..ecbced1 100644
> > --- a/net/sunrpc/xprtsock.c
> > +++ b/net/sunrpc/xprtsock.c
> > @@ -37,6 +37,7 @@
> >  #include <linux/sunrpc/svcsock.h>
> >  #include <linux/sunrpc/xprtsock.h>
> >  #include <linux/file.h>
> > +#include <linux/fs_struct.h>
> >  #ifdef CONFIG_SUNRPC_BACKCHANNEL
> >  #include <linux/sunrpc/bc_xprt.h>
> >  #endif
> > @@ -255,6 +256,11 @@ struct sock_xprt {
> >  	void			(*old_state_change)(struct sock *);
> >  	void			(*old_write_space)(struct sock *);
> >  	void			(*old_error_report)(struct sock *);
> > +
> > +	/*
> > +	 * Saved transport creator root. Required for local transports only.
> > +	 */
> > +	struct path		root;
> >  };
> >  
> >  /*
> > @@ -1876,6 +1882,30 @@ static int xs_local_finish_connecting(struct rpc_xprt *xprt,
> >  	return kernel_connect(sock, xs_addr(xprt), xprt->addrlen, 0);
> >  }
> >  
> > +/*
> > + * __xs_local_swap_root - swap current root to tranport's root helper.
> > + * @new_root - path to set to current fs->root.
> > + * @old_root - optinal paoinet to save current root to
> > + *
> > + * This routine is requieed to connecting unix sockets to absolute path in
> > + * proper root environment.
> > + * Note: no path_get() will be called. I.e. caller have to hold reference to
> > + * new_root.
> > + */
> > +static void __xs_local_swap_root(struct path *new_root, struct path *old_root)
> > +{
> > +	struct fs_struct *fs = current->fs;
> > +
> > +	spin_lock(&fs->lock);
> > +	write_seqcount_begin(&fs->seq);
> > +	if (old_root)
> > +		*old_root = fs->root;
> > +	fs->root = *new_root;
> > +	write_seqcount_end(&fs->seq);
> > +	spin_unlock(&fs->lock);
> > +}
> > +
> > +
> >  /**
> >   * xs_local_setup_socket - create AF_LOCAL socket, connect to a local endpoint
> >   * @xprt: RPC transport to connect
> > @@ -1891,6 +1921,7 @@ static void xs_local_setup_socket(struct work_struct *work)
> >  	struct rpc_xprt *xprt = &transport->xprt;
> >  	struct socket *sock;
> >  	int status = -EIO;
> > +	struct path root;
> >  
> >  	current->flags |= PF_FSTRANS;
> >  
> > @@ -1907,7 +1938,10 @@ static void xs_local_setup_socket(struct work_struct *work)
> >  	dprintk("RPC:       worker connecting xprt %p via AF_LOCAL to %s\n",
> >  			xprt, xprt->address_strings[RPC_DISPLAY_ADDR]);
> >  
> > +	__xs_local_swap_root(&transport->root, &root);
> >  	status = xs_local_finish_connecting(xprt, sock);
> > +	__xs_local_swap_root(&root, NULL);
> > +
> >  	switch (status) {
> >  	case 0:
> >  		dprintk("RPC:       xprt %p connected to %s\n",
> > @@ -2256,6 +2290,18 @@ static void xs_connect(struct rpc_task *task)
> >  	}
> >  }
> >  
> > +static void xs_local_destroy(struct rpc_xprt *xprt)
> > +{
> > +	struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt);
> > +	struct path root = transport->root;
> > +
> > +	dprintk("RPC:       xs_local_destroy xprt %p\n", xprt);
> > +
> > +	xs_destroy(xprt);
> > +
> > +	path_put(&root);
> > +}
> > +
> >  /**
> >   * xs_local_print_stats - display AF_LOCAL socket-specifc stats
> >   * @xprt: rpc_xprt struct containing statistics
> > @@ -2475,7 +2521,7 @@ static struct rpc_xprt_ops xs_local_ops = {
> >  	.send_request		= xs_local_send_request,
> >  	.set_retrans_timeout	= xprt_set_retrans_timeout_def,
> >  	.close			= xs_close,
> > -	.destroy		= xs_destroy,
> > +	.destroy		= xs_local_destroy,
> >  	.print_stats		= xs_local_print_stats,
> >  };
> >  
> > @@ -2654,8 +2700,10 @@ static struct rpc_xprt *xs_setup_local(struct xprt_create *args)
> >  	dprintk("RPC:       set up xprt to %s via AF_LOCAL\n",
> >  			xprt->address_strings[RPC_DISPLAY_ADDR]);
> >  
> > -	if (try_module_get(THIS_MODULE))
> > +	if (try_module_get(THIS_MODULE)) {
> > +		get_fs_root(current->fs, &transport->root);
> >  		return xprt;
> > +	}
> >  	ret = ERR_PTR(-EINVAL);
> >  out_err:
> >  	xprt_free(xprt);
> > 

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com
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Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Eric W. Biederman]

"Myklebust, Trond" <Trond.Myklebust@netapp.com> writes:

> On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
>> Cc'ing Eric since I seem to recall he suggested doing it this way?

Yes.  On second look setting fs->root won't work. We need to change fs.
The problem is that by default all kernel threads share fs so changing
fs->root will have non-local consequences.

I very much believe we want if at all possible to perform a local
modification.

Changing fs isn't all that different from what devtmpfs is doing.

>> Seems OK to me, but maybe that swap_root should be in common code?  (Or
>> maybe we could use set_fs_root()?)
>> 
>> I'm assuming it's up to Trond to take this.--b.
>
> I'm reluctant to do that at this time since the original proposal was
> precisely that of export set_fs_root() and using it around the AF_LOCAL
> socket bind. That proposal was NACKed by Al Viro.

> If Al is OK with the idea of us creating a private version of
> set_fs_root, then I'd like to see an official Acked-by: that we can
> append to this commit.

Eric

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
> "Myklebust, Trond" <Trond.Myklebust@netapp.com> writes:
> 
> > On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
> >> Cc'ing Eric since I seem to recall he suggested doing it this way?
> 
> Yes.  On second look setting fs->root won't work. We need to change fs.
> The problem is that by default all kernel threads share fs so changing
> fs->root will have non-local consequences.

Oh, huh.  And we can't "unshare" it somehow?

Or, previously you suggested:

	- introduce sockaddr_fd that can be applied to AF_UNIX sockets,
	  and teach unix_bind and unix_connect how to deal with a second
	  type of sockaddr, AT_FD:
	  struct sockaddr_fd { short fd_family; short pad; int fd; }

	- introduce sockaddr_unix_at that takes a directory file
	  descriptor as well as a unix path, and teach unix_bind and
	  unix_connect to deal with a second sockaddr type, AF_UNIX_AT:
	  struct sockaddr_unix_at { short family; short pad; int dfd; char path[102]; }

Any other options?

> I very much believe we want if at all possible to perform a local
> modification.
> 
> Changing fs isn't all that different from what devtmpfs is doing.

Sorry, I don't know much about devtmpfs, are you suggesting it as a
model?  What exactly should we look at?

--b.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Eric W. Biederman]

"J. Bruce Fields" <bfields@fieldses.org> writes:

> On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
>> "Myklebust, Trond" <Trond.Myklebust@netapp.com> writes:
>> 
>> > On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
>> >> Cc'ing Eric since I seem to recall he suggested doing it this way?
>> 
>> Yes.  On second look setting fs->root won't work. We need to change fs.
>> The problem is that by default all kernel threads share fs so changing
>> fs->root will have non-local consequences.
>
> Oh, huh.  And we can't "unshare" it somehow?

I don't fully understand how nfs uses kernel threads and work queues.
My general understanding is work queues reuse their kernel threads
between different users.  So it is mostly a don't pollute your
environment thing.  If there was a dedicated kernel thread for each
environment this would be trivial.

What I was suggesting here is changing task->fs instead of
task->fs.root.  That should just require task_lock().

> Or, previously you suggested:
>
> 	- introduce sockaddr_fd that can be applied to AF_UNIX sockets,
> 	  and teach unix_bind and unix_connect how to deal with a second
> 	  type of sockaddr, AT_FD:
> 	  struct sockaddr_fd { short fd_family; short pad; int fd; }
>
> 	- introduce sockaddr_unix_at that takes a directory file
> 	  descriptor as well as a unix path, and teach unix_bind and
> 	  unix_connect to deal with a second sockaddr type, AF_UNIX_AT:
> 	  struct sockaddr_unix_at { short family; short pad; int dfd; char path[102]; }
>
> Any other options?

I am still half hoping we don't have to change the userspace API/ABI.
There is sanity checking on that path that no one seems interested in to
solve this problem.

This is a weird issue as we are dealing with both the vfs and the
networking stack.  Fundamentally we need to change task->fs.root or
we need to capitialize on the openat functionality in the kernel, so
that we don't create mountains of special cases to support this.

I think swapping task->fs instead of task->fs.root is effecitely the
same complexity.

>> I very much believe we want if at all possible to perform a local
>> modification.
>> 
>> Changing fs isn't all that different from what devtmpfs is doing.
>
> Sorry, I don't know much about devtmpfs, are you suggesting it as a
> model?  What exactly should we look at?

Roughly all I meant was that devtmpsfsd is a kernel thread that runs
with an unshared fs struct.  Although I admit devtmpfsd is for all
practical purposes a userspace daemon that just happens to run in kernel
space.

Eric

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Tue, Oct 09, 2012 at 03:47:42PM -0700, Eric W. Biederman wrote:
> "J. Bruce Fields" <bfields@fieldses.org> writes:
> 
> > On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
> >> "Myklebust, Trond" <Trond.Myklebust@netapp.com> writes:
> >> 
> >> > On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
> >> >> Cc'ing Eric since I seem to recall he suggested doing it this way?
> >> 
> >> Yes.  On second look setting fs->root won't work. We need to change fs.
> >> The problem is that by default all kernel threads share fs so changing
> >> fs->root will have non-local consequences.
> >
> > Oh, huh.  And we can't "unshare" it somehow?
> 
> I don't fully understand how nfs uses kernel threads and work queues.
> My general understanding is work queues reuse their kernel threads
> between different users.  So it is mostly a don't pollute your
> environment thing.  If there was a dedicated kernel thread for each
> environment this would be trivial.
> 
> What I was suggesting here is changing task->fs instead of
> task->fs.root.  That should just require task_lock().

Oh, OK, got it--if that works, great.

> > Sorry, I don't know much about devtmpfs, are you suggesting it as a
> > model?  What exactly should we look at?
> 
> Roughly all I meant was that devtmpsfsd is a kernel thread that runs
> with an unshared fs struct.  Although I admit devtmpfsd is for all
> practical purposes a userspace daemon that just happens to run in kernel
> space.

Thanks for the explanation.

--b.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Eric W. Biederman]

ebiederm@xmission.com (Eric W. Biederman) writes:

> "J. Bruce Fields" <bfields@fieldses.org> writes:
>
>> On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
>>> "Myklebust, Trond" <Trond.Myklebust@netapp.com> writes:
>>> 
>>> > On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
>>> >> Cc'ing Eric since I seem to recall he suggested doing it this way?
>>> 
>>> Yes.  On second look setting fs->root won't work. We need to change fs.
>>> The problem is that by default all kernel threads share fs so changing
>>> fs->root will have non-local consequences.
>>
>> Oh, huh.  And we can't "unshare" it somehow?
>
> I don't fully understand how nfs uses kernel threads and work queues.
> My general understanding is work queues reuse their kernel threads
> between different users.  So it is mostly a don't pollute your
> environment thing.  If there was a dedicated kernel thread for each
> environment this would be trivial.
>
> What I was suggesting here is changing task->fs instead of
> task->fs.root.  That should just require task_lock().
>
>> Or, previously you suggested:
>>
>> 	- introduce sockaddr_fd that can be applied to AF_UNIX sockets,
>> 	  and teach unix_bind and unix_connect how to deal with a second
>> 	  type of sockaddr, AT_FD:
>> 	  struct sockaddr_fd { short fd_family; short pad; int fd; }
>>
>> 	- introduce sockaddr_unix_at that takes a directory file
>> 	  descriptor as well as a unix path, and teach unix_bind and
>> 	  unix_connect to deal with a second sockaddr type, AF_UNIX_AT:
>> 	  struct sockaddr_unix_at { short family; short pad; int dfd; char path[102]; }
>>
>> Any other options?
>
> I am still half hoping we don't have to change the userspace API/ABI.
> There is sanity checking on that path that no one seems interested in to
> solve this problem.

There is a good option if we are up to userspace ABI extensions.

Implement open(2) on unix domain sockets.  Where open(2) would
essentially equal connect(2) on unix domain sockets.

With an open(2) implementation we could use file_open_path and the
implementation should be pretty straight forward and maintainable.
So implementing open(2) looks like a good alternative implementation
route.

Eric

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Stanislav Kinsbursky]

10.10.2012 02:47, Eric W. Biederman пишет:
> "J. Bruce Fields" <bfields@fieldses.org> writes:
>
>> On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
>>> "Myklebust, Trond" <Trond.Myklebust@netapp.com> writes:
>>>
>>>> On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
>>>>> Cc'ing Eric since I seem to recall he suggested doing it this way?
>>> Yes.  On second look setting fs->root won't work. We need to change fs.
>>> The problem is that by default all kernel threads share fs so changing
>>> fs->root will have non-local consequences.
>> Oh, huh.  And we can't "unshare" it somehow?
> I don't fully understand how nfs uses kernel threads and work queues.
> My general understanding is work queues reuse their kernel threads
> between different users.  So it is mostly a don't pollute your
> environment thing.  If there was a dedicated kernel thread for each
> environment this would be trivial.

One kernel thread per environment is exactly what we are trying to avoid 
if possible.
And the reason why we don't want to do this is that it's really looks 
like overkill.

> What I was suggesting here is changing task->fs instead of
> task->fs.root.  That should just require task_lock().
>
>> Or, previously you suggested:
>>
>> 	- introduce sockaddr_fd that can be applied to AF_UNIX sockets,
>> 	  and teach unix_bind and unix_connect how to deal with a second
>> 	  type of sockaddr, AT_FD:
>> 	  struct sockaddr_fd { short fd_family; short pad; int fd; }
>>
>> 	- introduce sockaddr_unix_at that takes a directory file
>> 	  descriptor as well as a unix path, and teach unix_bind and
>> 	  unix_connect to deal with a second sockaddr type, AF_UNIX_AT:
>> 	  struct sockaddr_unix_at { short family; short pad; int dfd; char path[102]; }
>>
>> Any other options?
> I am still half hoping we don't have to change the userspace API/ABI.
> There is sanity checking on that path that no one seems interested in to
> solve this problem.
>
> This is a weird issue as we are dealing with both the vfs and the
> networking stack.  Fundamentally we need to change task->fs.root or
> we need to capitialize on the openat functionality in the kernel, so
> that we don't create mountains of special cases to support this.
>
> I think swapping task->fs instead of task->fs.root is effecitely the
> same complexity.

Thanks for the idea. And for mentioning, that kernel threads shares fs 
struct. I missed it.

>
>>> I very much believe we want if at all possible to perform a local
>>> modification.
>>>
>>> Changing fs isn't all that different from what devtmpfs is doing.
>> Sorry, I don't know much about devtmpfs, are you suggesting it as a
>> model?  What exactly should we look at?
> Roughly all I meant was that devtmpsfsd is a kernel thread that runs
> with an unshared fs struct.  Although I admit devtmpfsd is for all
> practical purposes a userspace daemon that just happens to run in kernel
> space.
>
> Eric
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Stanislav Kinsbursky]

10.10.2012 06:00, Eric W. Biederman пишет:
> ebiederm@xmission.com (Eric W. Biederman) writes:
>
>> "J. Bruce Fields" <bfields@fieldses.org> writes:
>>
>>> On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
>>>> "Myklebust, Trond" <Trond.Myklebust@netapp.com> writes:
>>>>
>>>>> On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
>>>>>> Cc'ing Eric since I seem to recall he suggested doing it this way?
>>>> Yes.  On second look setting fs->root won't work. We need to change fs.
>>>> The problem is that by default all kernel threads share fs so changing
>>>> fs->root will have non-local consequences.
>>> Oh, huh.  And we can't "unshare" it somehow?
>> I don't fully understand how nfs uses kernel threads and work queues.
>> My general understanding is work queues reuse their kernel threads
>> between different users.  So it is mostly a don't pollute your
>> environment thing.  If there was a dedicated kernel thread for each
>> environment this would be trivial.
>>
>> What I was suggesting here is changing task->fs instead of
>> task->fs.root.  That should just require task_lock().
>>
>>> Or, previously you suggested:
>>>
>>> 	- introduce sockaddr_fd that can be applied to AF_UNIX sockets,
>>> 	  and teach unix_bind and unix_connect how to deal with a second
>>> 	  type of sockaddr, AT_FD:
>>> 	  struct sockaddr_fd { short fd_family; short pad; int fd; }
>>>
>>> 	- introduce sockaddr_unix_at that takes a directory file
>>> 	  descriptor as well as a unix path, and teach unix_bind and
>>> 	  unix_connect to deal with a second sockaddr type, AF_UNIX_AT:
>>> 	  struct sockaddr_unix_at { short family; short pad; int dfd; char path[102]; }
>>>
>>> Any other options?
>> I am still half hoping we don't have to change the userspace API/ABI.
>> There is sanity checking on that path that no one seems interested in to
>> solve this problem.
> There is a good option if we are up to userspace ABI extensions.
>
> Implement open(2) on unix domain sockets.  Where open(2) would
> essentially equal connect(2) on unix domain sockets.
>
> With an open(2) implementation we could use file_open_path and the
> implementation should be pretty straight forward and maintainable.
> So implementing open(2) looks like a good alternative implementation
> route.

This requires patching of vfs layer as well. I don't want to say, that 
the idea is not good. But it requires much more time to implement and test.
And this patch addresses the problem, which exist already and would be 
great to fix it as soon as possible.
So, probably, implementing open for unix sockets is the next and more 
generic step.
Thanks.

> Eric
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Stanislav Kinsbursky]

10.10.2012 05:23, J. Bruce Fields пишет:
> On Tue, Oct 09, 2012 at 03:47:42PM -0700, Eric W. Biederman wrote:
>> "J. Bruce Fields" <bfields@fieldses.org> writes:
>>
>>> On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
>>>> "Myklebust, Trond" <Trond.Myklebust@netapp.com> writes:
>>>>
>>>>> On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
>>>>>> Cc'ing Eric since I seem to recall he suggested doing it this way?
>>>>
>>>> Yes.  On second look setting fs->root won't work. We need to change fs.
>>>> The problem is that by default all kernel threads share fs so changing
>>>> fs->root will have non-local consequences.
>>>
>>> Oh, huh.  And we can't "unshare" it somehow?
>>
>> I don't fully understand how nfs uses kernel threads and work queues.
>> My general understanding is work queues reuse their kernel threads
>> between different users.  So it is mostly a don't pollute your
>> environment thing.  If there was a dedicated kernel thread for each
>> environment this would be trivial.
>>
>> What I was suggesting here is changing task->fs instead of
>> task->fs.root.  That should just require task_lock().
>
> Oh, OK, got it--if that works, great.
>

The main problem with swapping fs struct is actually the same as in root 
swapping. I.e. routines for copy fs_struct are not exported.
It could be done on place, but I don't think, that Al Viro would support such 
implementation.
Trond?

>>> Sorry, I don't know much about devtmpfs, are you suggesting it as a
>>> model?  What exactly should we look at?
>>
>> Roughly all I meant was that devtmpsfsd is a kernel thread that runs
>> with an unshared fs struct.  Although I admit devtmpfsd is for all
>> practical purposes a userspace daemon that just happens to run in kernel
>> space.
>
> Thanks for the explanation.
>
> --b.
>


-- 
Best regards,
Stanislav Kinsbursky

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Wed, Oct 10, 2012 at 02:32:28PM +0400, Stanislav Kinsbursky wrote:
> 10.10.2012 05:23, J. Bruce Fields пишет:
> >On Tue, Oct 09, 2012 at 03:47:42PM -0700, Eric W. Biederman wrote:
> >>"J. Bruce Fields" <bfields@fieldses.org> writes:
> >>
> >>>On Tue, Oct 09, 2012 at 01:20:48PM -0700, Eric W. Biederman wrote:
> >>>>"Myklebust, Trond" <Trond.Myklebust@netapp.com> writes:
> >>>>
> >>>>>On Tue, 2012-10-09 at 15:35 -0400, J. Bruce Fields wrote:
> >>>>>>Cc'ing Eric since I seem to recall he suggested doing it this way?
> >>>>
> >>>>Yes.  On second look setting fs->root won't work. We need to change fs.
> >>>>The problem is that by default all kernel threads share fs so changing
> >>>>fs->root will have non-local consequences.
> >>>
> >>>Oh, huh.  And we can't "unshare" it somehow?
> >>
> >>I don't fully understand how nfs uses kernel threads and work queues.
> >>My general understanding is work queues reuse their kernel threads
> >>between different users.  So it is mostly a don't pollute your
> >>environment thing.  If there was a dedicated kernel thread for each
> >>environment this would be trivial.
> >>
> >>What I was suggesting here is changing task->fs instead of
> >>task->fs.root.  That should just require task_lock().
> >
> >Oh, OK, got it--if that works, great.
> >
> 
> The main problem with swapping fs struct is actually the same as in
> root swapping. I.e. routines for copy fs_struct are not exported.
> It could be done on place, but I don't think, that Al Viro would
> support such implementation.
> Trond?

It seems like we got stalled here....  Could you go ahead and try a
patch, and see what people think?

--b.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Stanislav Kinsbursky]

09.10.2012 23:35, J. Bruce Fields пишет:
> Cc'ing Eric since I seem to recall he suggested doing it this way?
>
> Seems OK to me, but maybe that swap_root should be in common code?  (Or
> maybe we could use set_fs_root()?)
>

This patch is not good since, as Eric mentioned, all kernel threads share same 
fs struct.
We can swap whole fs struct. Or we can unshare fs struct (unshare_fs_struct() is 
exported) and swap root in this case.
But this approach is to close to set_fs_root() logic, which is not exported and 
seems there are some valid reasons for it.

> I'm assuming it's up to Trond to take this.--b.
>
> On Mon, Oct 08, 2012 at 02:56:32PM +0400, Stanislav Kinsbursky wrote:
>> Today, there is a problem in connecting of local SUNRPC thansports. These
>> transports uses UNIX sockets and connection itself is done by rpciod
>> workqueue.
>> But all local transports are connecting in rpciod context. I.e. UNIX sockets
>> lookup is done in context of process file system root.
>> This works nice until we will try to mount NFS from process with other root -
>> for example in container. This container can have it's own (nested) root and
>> rcpbind process, listening on it's own unix sockets. But NFS mount attempt in
>> this container will register new service (Lockd for example) in global rpcbind
>> - not containers's one.
>> This patch solves the problem by switching rpciod kernel thread's file system
>> root to the right one (stored on transport) while connecting of local
>> transports.
>>
>> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
>> ---
>>   net/sunrpc/xprtsock.c |   52 +++++++++++++++++++++++++++++++++++++++++++++++--
>>   1 files changed, 50 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
>> index aaaadfb..ecbced1 100644
>> --- a/net/sunrpc/xprtsock.c
>> +++ b/net/sunrpc/xprtsock.c
>> @@ -37,6 +37,7 @@
>>   #include <linux/sunrpc/svcsock.h>
>>   #include <linux/sunrpc/xprtsock.h>
>>   #include <linux/file.h>
>> +#include <linux/fs_struct.h>
>>   #ifdef CONFIG_SUNRPC_BACKCHANNEL
>>   #include <linux/sunrpc/bc_xprt.h>
>>   #endif
>> @@ -255,6 +256,11 @@ struct sock_xprt {
>>   	void			(*old_state_change)(struct sock *);
>>   	void			(*old_write_space)(struct sock *);
>>   	void			(*old_error_report)(struct sock *);
>> +
>> +	/*
>> +	 * Saved transport creator root. Required for local transports only.
>> +	 */
>> +	struct path		root;
>>   };
>>
>>   /*
>> @@ -1876,6 +1882,30 @@ static int xs_local_finish_connecting(struct rpc_xprt *xprt,
>>   	return kernel_connect(sock, xs_addr(xprt), xprt->addrlen, 0);
>>   }
>>
>> +/*
>> + * __xs_local_swap_root - swap current root to tranport's root helper.
>> + * @new_root - path to set to current fs->root.
>> + * @old_root - optinal paoinet to save current root to
>> + *
>> + * This routine is requieed to connecting unix sockets to absolute path in
>> + * proper root environment.
>> + * Note: no path_get() will be called. I.e. caller have to hold reference to
>> + * new_root.
>> + */
>> +static void __xs_local_swap_root(struct path *new_root, struct path *old_root)
>> +{
>> +	struct fs_struct *fs = current->fs;
>> +
>> +	spin_lock(&fs->lock);
>> +	write_seqcount_begin(&fs->seq);
>> +	if (old_root)
>> +		*old_root = fs->root;
>> +	fs->root = *new_root;
>> +	write_seqcount_end(&fs->seq);
>> +	spin_unlock(&fs->lock);
>> +}
>> +
>> +
>>   /**
>>    * xs_local_setup_socket - create AF_LOCAL socket, connect to a local endpoint
>>    * @xprt: RPC transport to connect
>> @@ -1891,6 +1921,7 @@ static void xs_local_setup_socket(struct work_struct *work)
>>   	struct rpc_xprt *xprt = &transport->xprt;
>>   	struct socket *sock;
>>   	int status = -EIO;
>> +	struct path root;
>>
>>   	current->flags |= PF_FSTRANS;
>>
>> @@ -1907,7 +1938,10 @@ static void xs_local_setup_socket(struct work_struct *work)
>>   	dprintk("RPC:       worker connecting xprt %p via AF_LOCAL to %s\n",
>>   			xprt, xprt->address_strings[RPC_DISPLAY_ADDR]);
>>
>> +	__xs_local_swap_root(&transport->root, &root);
>>   	status = xs_local_finish_connecting(xprt, sock);
>> +	__xs_local_swap_root(&root, NULL);
>> +
>>   	switch (status) {
>>   	case 0:
>>   		dprintk("RPC:       xprt %p connected to %s\n",
>> @@ -2256,6 +2290,18 @@ static void xs_connect(struct rpc_task *task)
>>   	}
>>   }
>>
>> +static void xs_local_destroy(struct rpc_xprt *xprt)
>> +{
>> +	struct sock_xprt *transport = container_of(xprt, struct sock_xprt, xprt);
>> +	struct path root = transport->root;
>> +
>> +	dprintk("RPC:       xs_local_destroy xprt %p\n", xprt);
>> +
>> +	xs_destroy(xprt);
>> +
>> +	path_put(&root);
>> +}
>> +
>>   /**
>>    * xs_local_print_stats - display AF_LOCAL socket-specifc stats
>>    * @xprt: rpc_xprt struct containing statistics
>> @@ -2475,7 +2521,7 @@ static struct rpc_xprt_ops xs_local_ops = {
>>   	.send_request		= xs_local_send_request,
>>   	.set_retrans_timeout	= xprt_set_retrans_timeout_def,
>>   	.close			= xs_close,
>> -	.destroy		= xs_destroy,
>> +	.destroy		= xs_local_destroy,
>>   	.print_stats		= xs_local_print_stats,
>>   };
>>
>> @@ -2654,8 +2700,10 @@ static struct rpc_xprt *xs_setup_local(struct xprt_create *args)
>>   	dprintk("RPC:       set up xprt to %s via AF_LOCAL\n",
>>   			xprt->address_strings[RPC_DISPLAY_ADDR]);
>>
>> -	if (try_module_get(THIS_MODULE))
>> +	if (try_module_get(THIS_MODULE)) {
>> +		get_fs_root(current->fs, &transport->root);
>>   		return xprt;
>> +	}
>>   	ret = ERR_PTR(-EINVAL);
>>   out_err:
>>   	xprt_free(xprt);
>>


-- 
Best regards,
Stanislav Kinsbursky

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Tue, Nov 06, 2012 at 02:14:50PM +0400, Stanislav Kinsbursky wrote:
> 09.10.2012 23:35, J. Bruce Fields пишет:
> >Cc'ing Eric since I seem to recall he suggested doing it this way?
> >
> >Seems OK to me, but maybe that swap_root should be in common code?  (Or
> >maybe we could use set_fs_root()?)
> >
> 
> This patch is not good since, as Eric mentioned, all kernel threads
> share same fs struct.
> We can swap whole fs struct. Or we can unshare fs struct
> (unshare_fs_struct() is exported) and swap root in this case.
> But this approach is to close to set_fs_root() logic, which is not
> exported and seems there are some valid reasons for it.

What are those reasons?

Googling found one previous thread:

	http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687

There Trond requests an ACK from Al or Cristoph for the export, but I
don't see either an ACK or any objection.

--b.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Stanislav Kinsbursky]

06.11.2012 16:06, J. Bruce Fields пишет:
> On Tue, Nov 06, 2012 at 02:14:50PM +0400, Stanislav Kinsbursky wrote:
>> 09.10.2012 23:35, J. Bruce Fields пишет:
>>> Cc'ing Eric since I seem to recall he suggested doing it this way?
>>>
>>> Seems OK to me, but maybe that swap_root should be in common code?  (Or
>>> maybe we could use set_fs_root()?)
>>>
>>
>> This patch is not good since, as Eric mentioned, all kernel threads
>> share same fs struct.
>> We can swap whole fs struct. Or we can unshare fs struct
>> (unshare_fs_struct() is exported) and swap root in this case.
>> But this approach is to close to set_fs_root() logic, which is not
>> exported and seems there are some valid reasons for it.
>
> What are those reasons?
>

I don't know them.
Trond told, that Al doesn't like the idea of set_fs_root() exporting.

> Googling found one previous thread:
>
> 	http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
>
> There Trond requests an ACK from Al or Cristoph for the export, but I
> don't see either an ACK or any objection.
>

Cristoph told me on LSF something line "No ... way", when I asked him about 
set_fs_root() exporting.
But I had no opportunity to ask why.

> --b.
>


-- 
Best regards,
Stanislav Kinsbursky

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Christoph Hellwig]

On Tue, Nov 06, 2012 at 07:06:42AM -0500, J. Bruce Fields wrote:
> On Tue, Nov 06, 2012 at 02:14:50PM +0400, Stanislav Kinsbursky wrote:
> > 09.10.2012 23:35, J. Bruce Fields ??????????:
> > >Cc'ing Eric since I seem to recall he suggested doing it this way?
> > >
> > >Seems OK to me, but maybe that swap_root should be in common code?  (Or
> > >maybe we could use set_fs_root()?)
> > >
> > 
> > This patch is not good since, as Eric mentioned, all kernel threads
> > share same fs struct.
> > We can swap whole fs struct. Or we can unshare fs struct
> > (unshare_fs_struct() is exported) and swap root in this case.
> > But this approach is to close to set_fs_root() logic, which is not
> > exported and seems there are some valid reasons for it.
> 
> What are those reasons?
> 
> Googling found one previous thread:
> 
> 	http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> 
> There Trond requests an ACK from Al or Cristoph for the export, but I
> don't see either an ACK or any objection.

I really don't think messing with current->fs for workqueue worker
threads is a good idea, as the worker threads are shared by different
workqueues and thus this can easily cause havoc for entirely unrelated
subsystems.

To do this properly you'll need to avoid current->fs references in the
sunrpc code.

And just in case it wasn't clear: the hack in this iteration is even
worse than the original.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Tue, Nov 06, 2012 at 04:11:11PM +0400, Stanislav Kinsbursky wrote:
> 06.11.2012 16:06, J. Bruce Fields пишет:
> >On Tue, Nov 06, 2012 at 02:14:50PM +0400, Stanislav Kinsbursky wrote:
> >>09.10.2012 23:35, J. Bruce Fields пишет:
> >>>Cc'ing Eric since I seem to recall he suggested doing it this way?
> >>>
> >>>Seems OK to me, but maybe that swap_root should be in common code?  (Or
> >>>maybe we could use set_fs_root()?)
> >>>
> >>
> >>This patch is not good since, as Eric mentioned, all kernel threads
> >>share same fs struct.
> >>We can swap whole fs struct. Or we can unshare fs struct
> >>(unshare_fs_struct() is exported) and swap root in this case.
> >>But this approach is to close to set_fs_root() logic, which is not
> >>exported and seems there are some valid reasons for it.
> >
> >What are those reasons?
> >
> 
> I don't know them.
> Trond told, that Al doesn't like the idea of set_fs_root() exporting.
> 
> >Googling found one previous thread:
> >
> >	http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> >
> >There Trond requests an ACK from Al or Cristoph for the export, but I
> >don't see either an ACK or any objection.
> >
> 
> Cristoph told me on LSF something line "No ... way", when I asked
> him about set_fs_root() exporting.
> But I had no opportunity to ask why.

So, Al or Christoph: NFS calls up to rpcbind from the kernel using
AF_LOCAL, so it looks up a path when it connects.  We'd like to export
set_fs_root() so we can temporarily put our task in the right namespace
around the connect call.  Is that reasonable?

I just want to get a reason on record so we stop going in circles here.

--b.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Tue, Nov 06, 2012 at 07:40:35AM -0500, Christoph Hellwig wrote:
> On Tue, Nov 06, 2012 at 07:06:42AM -0500, J. Bruce Fields wrote:
> > On Tue, Nov 06, 2012 at 02:14:50PM +0400, Stanislav Kinsbursky wrote:
> > > 09.10.2012 23:35, J. Bruce Fields ??????????:
> > > >Cc'ing Eric since I seem to recall he suggested doing it this way?
> > > >
> > > >Seems OK to me, but maybe that swap_root should be in common code?  (Or
> > > >maybe we could use set_fs_root()?)
> > > >
> > > 
> > > This patch is not good since, as Eric mentioned, all kernel threads
> > > share same fs struct.
> > > We can swap whole fs struct. Or we can unshare fs struct
> > > (unshare_fs_struct() is exported) and swap root in this case.
> > > But this approach is to close to set_fs_root() logic, which is not
> > > exported and seems there are some valid reasons for it.
> > 
> > What are those reasons?
> > 
> > Googling found one previous thread:
> > 
> > 	http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> > 
> > There Trond requests an ACK from Al or Cristoph for the export, but I
> > don't see either an ACK or any objection.
> 
> I really don't think messing with current->fs for workqueue worker
> threads is a good idea, as the worker threads are shared by different
> workqueues and thus this can easily cause havoc for entirely unrelated
> subsystems.

So you're worried that a bug in the nfs code could modify the root and
then not restore it?

--b.

> 
> To do this properly you'll need to avoid current->fs references in the
> sunrpc code.
> 
> And just in case it wasn't clear: the hack in this iteration is even
> worse than the original.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Christoph Hellwig]

On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> So you're worried that a bug in the nfs code could modify the root and
> then not restore it?

At least the link you pointed to earlier never sets it back.  Instead
of messing with it I'd rather have the sunrpc code use vfs_path_lookup
and not care about current->fs->root at all.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
> On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> > So you're worried that a bug in the nfs code could modify the root and
> > then not restore it?
> 
> At least the link you pointed to earlier never sets it back.

This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687

	+	get_fs_root(current->fs, &root);
	+	set_fs_root(current->fs, &transport->root);
	+
	 	status = xs_local_finish_connecting(xprt, sock);
	+
	+	set_fs_root(current->fs, &root);
	+	path_put(&root);

> Instead
> of messing with it I'd rather have the sunrpc code use vfs_path_lookup
> and not care about current->fs->root at all.

The annoyance is that the lookup happens somewhere lower down in the
networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
need some new (internal) API.  We'd likely be the only user of that new
API.

--b.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
> On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
> > On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> > > So you're worried that a bug in the nfs code could modify the root and
> > > then not restore it?
> > 
> > At least the link you pointed to earlier never sets it back.
> 
> This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> 
> 	+	get_fs_root(current->fs, &root);
> 	+	set_fs_root(current->fs, &transport->root);
> 	+
> 	 	status = xs_local_finish_connecting(xprt, sock);
> 	+
> 	+	set_fs_root(current->fs, &root);
> 	+	path_put(&root);
> 
> > Instead
> > of messing with it I'd rather have the sunrpc code use vfs_path_lookup
> > and not care about current->fs->root at all.
> 
> The annoyance is that the lookup happens somewhere lower down in the
> networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
> need some new (internal) API.  We'd likely be the only user of that new
> API.

So, if the only drawback is really just the risk of introducing a bug
that leaves the fs_root changed--the above seems simple enough for that
not to be a great risk, right?

Is there any other hazard to doing this that people can think of?

--b.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Stanislav Kinsbursky]

07.11.2012 22:33, J. Bruce Fields пишет:
> On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
>> On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
>>> On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
>>>> So you're worried that a bug in the nfs code could modify the root and
>>>> then not restore it?
>>>
>>> At least the link you pointed to earlier never sets it back.
>>
>> This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
>>
>> 	+	get_fs_root(current->fs, &root);
>> 	+	set_fs_root(current->fs, &transport->root);
>> 	+
>> 	 	status = xs_local_finish_connecting(xprt, sock);
>> 	+
>> 	+	set_fs_root(current->fs, &root);
>> 	+	path_put(&root);
>>
>>> Instead
>>> of messing with it I'd rather have the sunrpc code use vfs_path_lookup
>>> and not care about current->fs->root at all.
>>
>> The annoyance is that the lookup happens somewhere lower down in the
>> networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
>> need some new (internal) API.  We'd likely be the only user of that new
>> API.
>
> So, if the only drawback is really just the risk of introducing a bug
> that leaves the fs_root changed--the above seems simple enough for that
> not to be a great risk, right?
>

If we unshare rpciod fs struct (which is exported already), then we won't affect 
other kthreads by root swapping.
But would be great to hear Trond's opinion about this approach.

Trond, could you tell us your feeling about all this?

> Is there any other hazard to doing this that people can think of?
>
> --b.
>


-- 
Best regards,
Stanislav Kinsbursky

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Mon, Nov 12, 2012 at 12:37:54PM +0400, Stanislav Kinsbursky wrote:
> 07.11.2012 22:33, J. Bruce Fields пишет:
> >On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
> >>On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
> >>>On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> >>>>So you're worried that a bug in the nfs code could modify the root and
> >>>>then not restore it?
> >>>
> >>>At least the link you pointed to earlier never sets it back.
> >>
> >>This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> >>
> >>	+	get_fs_root(current->fs, &root);
> >>	+	set_fs_root(current->fs, &transport->root);
> >>	+
> >>	 	status = xs_local_finish_connecting(xprt, sock);
> >>	+
> >>	+	set_fs_root(current->fs, &root);
> >>	+	path_put(&root);
> >>
> >>>Instead
> >>>of messing with it I'd rather have the sunrpc code use vfs_path_lookup
> >>>and not care about current->fs->root at all.
> >>
> >>The annoyance is that the lookup happens somewhere lower down in the
> >>networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
> >>need some new (internal) API.  We'd likely be the only user of that new
> >>API.
> >
> >So, if the only drawback is really just the risk of introducing a bug
> >that leaves the fs_root changed--the above seems simple enough for that
> >not to be a great risk, right?
> >
> 
> If we unshare rpciod fs struct (which is exported already), then we

I'm not sure what you mean by that.  Do workqueues actually have their
own dedicated set of associated tasks?  I thought all workqueues shared
a common pool of tasks these days.

> won't affect other kthreads by root swapping.
> But would be great to hear Trond's opinion about this approach.
> 
> Trond, could you tell us your feeling about all this?

I think it's often easier to get people to comment on an actual patch,
and this one would be quite short, so try that....

--b.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Myklebust, Trond]

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On Wed, 2012-11-14 at 16:01 -0500, J. Bruce Fields wrote:
> On Mon, Nov 12, 2012 at 12:37:54PM +0400, Stanislav Kinsbursky wrote:
> > 07.11.2012 22:33, J. Bruce Fields пишет:
> > >On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
> > >>On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
> > >>>On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> > >>>>So you're worried that a bug in the nfs code could modify the root and
> > >>>>then not restore it?
> > >>>
> > >>>At least the link you pointed to earlier never sets it back.
> > >>
> > >>This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> > >>
> > >>	+	get_fs_root(current->fs, &root);
> > >>	+	set_fs_root(current->fs, &transport->root);
> > >>	+
> > >>	 	status = xs_local_finish_connecting(xprt, sock);
> > >>	+
> > >>	+	set_fs_root(current->fs, &root);
> > >>	+	path_put(&root);
> > >>
> > >>>Instead
> > >>>of messing with it I'd rather have the sunrpc code use vfs_path_lookup
> > >>>and not care about current->fs->root at all.
> > >>
> > >>The annoyance is that the lookup happens somewhere lower down in the
> > >>networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
> > >>need some new (internal) API.  We'd likely be the only user of that new
> > >>API.
> > >
> > >So, if the only drawback is really just the risk of introducing a bug
> > >that leaves the fs_root changed--the above seems simple enough for that
> > >not to be a great risk, right?
> > >
> > 
> > If we unshare rpciod fs struct (which is exported already), then we
> 
> I'm not sure what you mean by that.  Do workqueues actually have their
> own dedicated set of associated tasks?  I thought all workqueues shared
> a common pool of tasks these days.
> 
> > won't affect other kthreads by root swapping.
> > But would be great to hear Trond's opinion about this approach.
> > 
> > Trond, could you tell us your feeling about all this?
> 
> I think it's often easier to get people to comment on an actual patch,
> and this one would be quite short, so try that....

unshare() would break expectations for other users of workqueue threads
unless you "reshare()" afterwards. Either way that's going to be
seriously ugly.

OK, let's look at this again. Do we ever use AF_LOCAL connections for
anything other than synchronous rpc calls to the local rpcbind daemon in
order to register/unregister new services? If not, then let's just move
the AF_LOCAL connection back into the process context and out of rpciod.

That implies that the process needs to be privileged, but it needs
privileges in order to start RPC daemons anyway.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com
ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Wed, Nov 14, 2012 at 09:36:33PM +0000, Myklebust, Trond wrote:
> On Wed, 2012-11-14 at 16:01 -0500, J. Bruce Fields wrote:
> > On Mon, Nov 12, 2012 at 12:37:54PM +0400, Stanislav Kinsbursky wrote:
> > > 07.11.2012 22:33, J. Bruce Fields пишет:
> > > >On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
> > > >>On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
> > > >>>On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> > > >>>>So you're worried that a bug in the nfs code could modify the root and
> > > >>>>then not restore it?
> > > >>>
> > > >>>At least the link you pointed to earlier never sets it back.
> > > >>
> > > >>This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> > > >>
> > > >>	+	get_fs_root(current->fs, &root);
> > > >>	+	set_fs_root(current->fs, &transport->root);
> > > >>	+
> > > >>	 	status = xs_local_finish_connecting(xprt, sock);
> > > >>	+
> > > >>	+	set_fs_root(current->fs, &root);
> > > >>	+	path_put(&root);
> > > >>
> > > >>>Instead
> > > >>>of messing with it I'd rather have the sunrpc code use vfs_path_lookup
> > > >>>and not care about current->fs->root at all.
> > > >>
> > > >>The annoyance is that the lookup happens somewhere lower down in the
> > > >>networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
> > > >>need some new (internal) API.  We'd likely be the only user of that new
> > > >>API.
> > > >
> > > >So, if the only drawback is really just the risk of introducing a bug
> > > >that leaves the fs_root changed--the above seems simple enough for that
> > > >not to be a great risk, right?
> > > >
> > > 
> > > If we unshare rpciod fs struct (which is exported already), then we
> > 
> > I'm not sure what you mean by that.  Do workqueues actually have their
> > own dedicated set of associated tasks?  I thought all workqueues shared
> > a common pool of tasks these days.
> > 
> > > won't affect other kthreads by root swapping.
> > > But would be great to hear Trond's opinion about this approach.
> > > 
> > > Trond, could you tell us your feeling about all this?
> > 
> > I think it's often easier to get people to comment on an actual patch,
> > and this one would be quite short, so try that....
> 
> unshare() would break expectations for other users of workqueue threads
> unless you "reshare()" afterwards. Either way that's going to be
> seriously ugly.
> 
> OK, let's look at this again. Do we ever use AF_LOCAL connections for
> anything other than synchronous rpc calls to the local rpcbind daemon in
> order to register/unregister new services?

Simo's patches use them for upcalls to svcgssd.  Those will always be
done from server threads.

> If not, then let's just move
> the AF_LOCAL connection back into the process context and out of rpciod.

Remind me how this helps?

--b.

> 
> That implies that the process needs to be privileged, but it needs
> privileges in order to start RPC daemons anyway.

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Myklebust, Trond]

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On Wed, 2012-11-14 at 16:42 -0500, J. Bruce Fields wrote:
> On Wed, Nov 14, 2012 at 09:36:33PM +0000, Myklebust, Trond wrote:
> > On Wed, 2012-11-14 at 16:01 -0500, J. Bruce Fields wrote:
> > > On Mon, Nov 12, 2012 at 12:37:54PM +0400, Stanislav Kinsbursky wrote:
> > > > 07.11.2012 22:33, J. Bruce Fields пишет:
> > > > >On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
> > > > >>On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
> > > > >>>On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
> > > > >>>>So you're worried that a bug in the nfs code could modify the root and
> > > > >>>>then not restore it?
> > > > >>>
> > > > >>>At least the link you pointed to earlier never sets it back.
> > > > >>
> > > > >>This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
> > > > >>
> > > > >>	+	get_fs_root(current->fs, &root);
> > > > >>	+	set_fs_root(current->fs, &transport->root);
> > > > >>	+
> > > > >>	 	status = xs_local_finish_connecting(xprt, sock);
> > > > >>	+
> > > > >>	+	set_fs_root(current->fs, &root);
> > > > >>	+	path_put(&root);
> > > > >>
> > > > >>>Instead
> > > > >>>of messing with it I'd rather have the sunrpc code use vfs_path_lookup
> > > > >>>and not care about current->fs->root at all.
> > > > >>
> > > > >>The annoyance is that the lookup happens somewhere lower down in the
> > > > >>networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
> > > > >>need some new (internal) API.  We'd likely be the only user of that new
> > > > >>API.
> > > > >
> > > > >So, if the only drawback is really just the risk of introducing a bug
> > > > >that leaves the fs_root changed--the above seems simple enough for that
> > > > >not to be a great risk, right?
> > > > >
> > > > 
> > > > If we unshare rpciod fs struct (which is exported already), then we
> > > 
> > > I'm not sure what you mean by that.  Do workqueues actually have their
> > > own dedicated set of associated tasks?  I thought all workqueues shared
> > > a common pool of tasks these days.
> > > 
> > > > won't affect other kthreads by root swapping.
> > > > But would be great to hear Trond's opinion about this approach.
> > > > 
> > > > Trond, could you tell us your feeling about all this?
> > > 
> > > I think it's often easier to get people to comment on an actual patch,
> > > and this one would be quite short, so try that....
> > 
> > unshare() would break expectations for other users of workqueue threads
> > unless you "reshare()" afterwards. Either way that's going to be
> > seriously ugly.
> > 
> > OK, let's look at this again. Do we ever use AF_LOCAL connections for
> > anything other than synchronous rpc calls to the local rpcbind daemon in
> > order to register/unregister new services?
> 
> Simo's patches use them for upcalls to svcgssd.  Those will always be
> done from server threads.

Any reason why you can't set that up when you start nfsd?

> > If not, then let's just move
> > the AF_LOCAL connection back into the process context and out of rpciod.
> 
> Remind me how this helps?

rpciod shares the 'init' process net namespace and chroot properties.
If, however you call bind() from the (containerised) process that was
used to start nfsd, then you will be using filesystem root (and net
namespace) of that container.

> --b.
> 
> > 
> > That implies that the process needs to be privileged, but it needs
> > privileges in order to start RPC daemons anyway.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com
ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Wed, Nov 14, 2012 at 09:51:33PM +0000, Myklebust, Trond wrote:
> On Wed, 2012-11-14 at 16:42 -0500, J. Bruce Fields wrote:
> > Simo's patches use them for upcalls to svcgssd.  Those will always be
> > done from server threads.
> 
> Any reason why you can't set that up when you start nfsd?

Oh, right, I was thinking of the upcalls themselves--right, the connect
we should be able to do on server start, I agree.

> 
> > > If not, then let's just move
> > > the AF_LOCAL connection back into the process context and out of rpciod.
> > 
> > Remind me how this helps?
> 
> rpciod shares the 'init' process net namespace and chroot properties.
> If, however you call bind() from the (containerised) process that was
> used to start nfsd, then you will be using filesystem root (and net
> namespace) of that container.

Got it.

--b.

> 
> > --b.
> > 
> > > 
> > > That implies that the process needs to be privileged, but it needs
> > > privileges in order to start RPC daemons anyway.
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer
> 
> NetApp
> Trond.Myklebust@netapp.com
> www.netapp.com

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Eric W. Biederman]

"J. Bruce Fields" <bfields@fieldses.org> writes:

> On Wed, Nov 14, 2012 at 09:51:33PM +0000, Myklebust, Trond wrote:
>> On Wed, 2012-11-14 at 16:42 -0500, J. Bruce Fields wrote:
>> > Simo's patches use them for upcalls to svcgssd.  Those will always be
>> > done from server threads.
>> 
>> Any reason why you can't set that up when you start nfsd?
>
> Oh, right, I was thinking of the upcalls themselves--right, the connect
> we should be able to do on server start, I agree.
>
>> 
>> > > If not, then let's just move
>> > > the AF_LOCAL connection back into the process context and out of rpciod.
>> > 
>> > Remind me how this helps?
>> 
>> rpciod shares the 'init' process net namespace and chroot properties.
>> If, however you call bind() from the (containerised) process that was
>> used to start nfsd, then you will be using filesystem root (and net
>> namespace) of that container.
>
> Got it.

If you can move the connect and bind into the server start that does
sound like a very good and maintainable solution.  I suspect it might
even be a smidge better for error handling.

Is there ever a reason to reconnect one of these sockets?

Eric

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Stanislav Kinsbursky]

15.11.2012 01:01, J. Bruce Fields пишет:
> On Mon, Nov 12, 2012 at 12:37:54PM +0400, Stanislav Kinsbursky wrote:
>> 07.11.2012 22:33, J. Bruce Fields пишет:
>>> On Tue, Nov 06, 2012 at 08:36:05AM -0500, J. Bruce Fields wrote:
>>>> On Tue, Nov 06, 2012 at 08:10:18AM -0500, Christoph Hellwig wrote:
>>>>> On Tue, Nov 06, 2012 at 08:07:06AM -0500, J. Bruce Fields wrote:
>>>>>> So you're worried that a bug in the nfs code could modify the root and
>>>>>> then not restore it?
>>>>>
>>>>> At least the link you pointed to earlier never sets it back.
>>>>
>>>> This? http://thread.gmane.org/gmane.linux.kernel/1259986/focus=47687
>>>>
>>>> 	+	get_fs_root(current->fs, &root);
>>>> 	+	set_fs_root(current->fs, &transport->root);
>>>> 	+
>>>> 	 	status = xs_local_finish_connecting(xprt, sock);
>>>> 	+
>>>> 	+	set_fs_root(current->fs, &root);
>>>> 	+	path_put(&root);
>>>>
>>>>> Instead
>>>>> of messing with it I'd rather have the sunrpc code use vfs_path_lookup
>>>>> and not care about current->fs->root at all.
>>>>
>>>> The annoyance is that the lookup happens somewhere lower down in the
>>>> networking code (net/unix/af_unix.c:unix_find_other, I think).  So we'd
>>>> need some new (internal) API.  We'd likely be the only user of that new
>>>> API.
>>>
>>> So, if the only drawback is really just the risk of introducing a bug
>>> that leaves the fs_root changed--the above seems simple enough for that
>>> not to be a great risk, right?
>>>
>>
>> If we unshare rpciod fs struct (which is exported already), then we
>
> I'm not sure what you mean by that.  Do workqueues actually have their
> own dedicated set of associated tasks?  I thought all workqueues shared
> a common pool of tasks these days.
>

Any kernel thread is cloned in kthreadd context with CLONE_FS flag.
I.e. all of them shares same fs struct, and changing fs->root in one of kthreads 
will affect all others.
That's why either fs struct have to be unshared to swap fs->root or fs->cwd, or 
the whole fs struct have to swapped.


-- 
Best regards,
Stanislav Kinsbursky

Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[Myklebust, Trond]

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On Wed, 2012-11-14 at 22:14 -0800, Eric W. Biederman wrote:
> "J. Bruce Fields" <bfields@fieldses.org> writes:
> 
> > On Wed, Nov 14, 2012 at 09:51:33PM +0000, Myklebust, Trond wrote:
> >> On Wed, 2012-11-14 at 16:42 -0500, J. Bruce Fields wrote:
> >> > Simo's patches use them for upcalls to svcgssd.  Those will always be
> >> > done from server threads.
> >> 
> >> Any reason why you can't set that up when you start nfsd?
> >
> > Oh, right, I was thinking of the upcalls themselves--right, the connect
> > we should be able to do on server start, I agree.
> >
> >> 
> >> > > If not, then let's just move
> >> > > the AF_LOCAL connection back into the process context and out of rpciod.
> >> > 
> >> > Remind me how this helps?
> >> 
> >> rpciod shares the 'init' process net namespace and chroot properties.
> >> If, however you call bind() from the (containerised) process that was
> >> used to start nfsd, then you will be using filesystem root (and net
> >> namespace) of that container.
> >
> > Got it.
> 
> If you can move the connect and bind into the server start that does
> sound like a very good and maintainable solution.  I suspect it might
> even be a smidge better for error handling.
> 
> Is there ever a reason to reconnect one of these sockets?

Not for the rpcbind case, however you can easily get into a situation
where the user restarts the gss daemon. The good news is that the gss
upcall code that uses AF_LOCAL hasn't been merged upstream yet, so that
particular interface is not yet locked in stone.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com
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Re: [PATCH v3] SUNRPC: set desired file system root before connecting local transports

[J. Bruce Fields]

On Thu, Nov 15, 2012 at 01:34:16PM +0000, Myklebust, Trond wrote:
> On Wed, 2012-11-14 at 22:14 -0800, Eric W. Biederman wrote:
> > "J. Bruce Fields" <bfields@fieldses.org> writes:
> > 
> > > On Wed, Nov 14, 2012 at 09:51:33PM +0000, Myklebust, Trond wrote:
> > >> On Wed, 2012-11-14 at 16:42 -0500, J. Bruce Fields wrote:
> > >> > Simo's patches use them for upcalls to svcgssd.  Those will always be
> > >> > done from server threads.
> > >> 
> > >> Any reason why you can't set that up when you start nfsd?
> > >
> > > Oh, right, I was thinking of the upcalls themselves--right, the connect
> > > we should be able to do on server start, I agree.
> > >
> > >> 
> > >> > > If not, then let's just move
> > >> > > the AF_LOCAL connection back into the process context and out of rpciod.
> > >> > 
> > >> > Remind me how this helps?
> > >> 
> > >> rpciod shares the 'init' process net namespace and chroot properties.
> > >> If, however you call bind() from the (containerised) process that was
> > >> used to start nfsd, then you will be using filesystem root (and net
> > >> namespace) of that container.
> > >
> > > Got it.
> > 
> > If you can move the connect and bind into the server start that does
> > sound like a very good and maintainable solution.  I suspect it might
> > even be a smidge better for error handling.
> > 
> > Is there ever a reason to reconnect one of these sockets?
> 
> Not for the rpcbind case, however you can easily get into a situation
> where the user restarts the gss daemon. The good news is that the gss
> upcall code that uses AF_LOCAL hasn't been merged upstream yet, so that
> particular interface is not yet locked in stone.

I think we do want to be able to allow the daemon to be restarted.

I guess we can have it call into the rpc server code when it starts up
and the server could do the connect then?  We need some way for
userspace to tell the server that the new upcall is supported anyway.

--b.