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

Stanislav Kinsbursky
2012-03-07T08:34:40Z

07.03.2012 04:19, Myklebust, Trond пишет:
> On Wed, 2012-02-29 at 18:59 +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 UNIX sockets lookup is done in context of process file system root. I.e.
>> all local thunsports are connecting in rpciod context.
>> 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 right one (stored on transport) while connecting of local transports.
>>
>> Signed-off-by: Stanislav Kinsbursky<skinsbursky@parallels.com>
>>
>> ---
>> fs/fs_struct.c | 1 +
>> net/sunrpc/xprtsock.c | 32 ++++++++++++++++++++++++++++++--
>> 2 files changed, 31 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/fs_struct.c b/fs/fs_struct.c
>> index 78b519c..0f984c3 100644
>> --- a/fs/fs_struct.c
>> +++ b/fs/fs_struct.c
>> @@ -36,6 +36,7 @@ void set_fs_root(struct fs_struct *fs, struct path *path)
>> if (old_root.dentry)
>> path_put_longterm(&old_root);
>> }
>> +EXPORT_SYMBOL_GPL(set_fs_root);
>>
>> /*
>> * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
>> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
>> index 4c8281d..c94c181 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;
>> };
>>
>> /*
>> @@ -1891,6 +1897,7 @@ 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;
>>
>> if (xprt->shutdown)
>> goto out;
>> @@ -1908,7 +1915,14 @@ 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]);
>>
>> + 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);
>> +
>> switch (status) {
>> case 0:
>
> Hi Stanislav,
>
> What happens here if the mount namespace of the process that originally
> created the sock_xprt no longer exists? Should we care about that case?
>

Hi, Trond.
Looks like this is not a problem, because process fs->root->mnt usage counter
was increased on transport creation.
IOW, transport holds current root and thus mount namespace can't disappear.

--
Best regards,
Stanislav Kinsbursky