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Date: Tue, 6 Nov 2012 14:14:50 +0400
From: Stanislav Kinsbursky <skinsbursky@...allels.com>
To: "J. Bruce Fields" <bfields@...ldses.org>
CC: "Trond.Myklebust@...app.com" <Trond.Myklebust@...app.com>,
"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"devel@...nvz.org" <devel@...nvz.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v3] SUNRPC: set desired file system root before connecting
local transports
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@...allels.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
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