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    Subject[PATCH 6/7] SUNRPC: pipefs per-net operations helper introduced
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    During per-net pipes creation and destruction we have to make sure, that pipefs
    sb exists for the whole creation/destruction cycle. This is done by using
    special mutex which controls pipefs sb reference on network namespace context.
    Helper consists of two parts: first of them (rpc_get_dentry_net) searches for
    dentry with specified name and returns with mutex taken on success. When pipe
    creation or destructions is completed, caller should release this mutex by
    rpc_put_dentry_net call.

    Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>

    ---
    include/linux/sunrpc/rpc_pipe_fs.h | 4 ++++
    net/sunrpc/netns.h | 1 +
    net/sunrpc/rpc_pipe.c | 36 ++++++++++++++++++++++++++++++++++++
    net/sunrpc/sunrpc_syms.c | 1 +
    4 files changed, 42 insertions(+), 0 deletions(-)

    diff --git a/include/linux/sunrpc/rpc_pipe_fs.h b/include/linux/sunrpc/rpc_pipe_fs.h
    index 4a327ad..271e1b2 100644
    --- a/include/linux/sunrpc/rpc_pipe_fs.h
    +++ b/include/linux/sunrpc/rpc_pipe_fs.h
    @@ -55,6 +55,10 @@ enum {
    extern struct dentry *rpc_d_lookup_sb(const struct super_block *sb,
    const unsigned char *dir_name);

    +extern void rpc_pipefs_init_net(struct net *net);
    +extern struct super_block *rpc_get_sb_net(const struct net *net);
    +extern void rpc_put_sb_net(const struct net *net);
    +
    extern int rpc_queue_upcall(struct inode *, struct rpc_pipe_msg *);

    struct rpc_clnt;
    diff --git a/net/sunrpc/netns.h b/net/sunrpc/netns.h
    index b384252..11d2f48 100644
    --- a/net/sunrpc/netns.h
    +++ b/net/sunrpc/netns.h
    @@ -11,6 +11,7 @@ struct sunrpc_net {
    struct cache_detail *ip_map_cache;

    struct super_block *pipefs_sb;
    + struct mutex pipefs_sb_lock;
    };

    extern int sunrpc_net_id;
    diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
    index 5c313d3..cbf213e 100644
    --- a/net/sunrpc/rpc_pipe.c
    +++ b/net/sunrpc/rpc_pipe.c
    @@ -1036,6 +1036,40 @@ struct dentry *rpc_d_lookup_sb(const struct super_block *sb,
    }
    EXPORT_SYMBOL_GPL(rpc_d_lookup_sb);

    +void rpc_pipefs_init_net(struct net *net)
    +{
    + struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
    +
    + mutex_init(&sn->pipefs_sb_lock);
    +}
    +
    +/*
    + * This call will be used for per network namespace operations calls.
    + * Note: Function will be returned with pipefs_sb_lock taken if superblock was
    + * found. This lock have to be released by rpc_put_sb_net() when all operations
    + * will be completed.
    + */
    +struct super_block *rpc_get_sb_net(const struct net *net)
    +{
    + struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
    +
    + mutex_lock(&sn->pipefs_sb_lock);
    + if (sn->pipefs_sb)
    + return sn->pipefs_sb;
    + mutex_unlock(&sn->pipefs_sb_lock);
    + return NULL;
    +}
    +EXPORT_SYMBOL_GPL(rpc_get_sb_net);
    +
    +void rpc_put_sb_net(const struct net *net)
    +{
    + struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
    +
    + BUG_ON(sn->pipefs_sb == NULL);
    + mutex_unlock(&sn->pipefs_sb_lock);
    +}
    +EXPORT_SYMBOL_GPL(rpc_put_sb_net);
    +
    static int
    rpc_fill_super(struct super_block *sb, void *data, int silent)
    {
    @@ -1090,7 +1124,9 @@ void rpc_kill_sb(struct super_block *sb)
    struct net *net = sb->s_fs_info;
    struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);

    + mutex_lock(&sn->pipefs_sb_lock);
    sn->pipefs_sb = NULL;
    + mutex_unlock(&sn->pipefs_sb_lock);
    put_net(net);
    blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
    RPC_PIPEFS_UMOUNT,
    diff --git a/net/sunrpc/sunrpc_syms.c b/net/sunrpc/sunrpc_syms.c
    index 9d08091..880de8b 100644
    --- a/net/sunrpc/sunrpc_syms.c
    +++ b/net/sunrpc/sunrpc_syms.c
    @@ -38,6 +38,7 @@ static __net_init int sunrpc_init_net(struct net *net)
    if (err)
    goto err_ipmap;

    + rpc_pipefs_init_net(net);
    return 0;

    err_ipmap:


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