NFS Client in Linux Kernel - cre

struct auth_cred

struct auth_cred记录着uid,gid,是最基本的cred信息。
通过current_cred()得到当前进程的struct auth_cred

struct rpc_auth

用来描述RPC传输时候使用哪种方式鉴权, Linux内核提供了4个unix_auth，null_auth，generic_auth，gss_auth,其中unix_auth是默认使用的。

struct rpc_auth {
    unsigned int        au_cslack;  /* call cred size estimate */
                /* guess at number of u32's auth adds before
                 * reply data; normally the verifier size: */
    unsigned int        au_rslack;
                /* for gss, used to calculate au_rslack: */
    unsigned int        au_verfsize;
    unsigned int        au_flags;   /* various flags */
    const struct rpc_authops *au_ops;       /* operations */
    rpc_authflavor_t    au_flavor;  /* pseudoflavor (note may
                         * differ from the flavor in
                         * au_ops->au_flavor in gss
                         * case) */
    atomic_t        au_count;   /* Reference counter */
    struct rpc_cred_cache * au_credcache;
    /* per-flavor data */
};

rpc auth flavors

鉴权方式，mount时候参数sec=xx,默认是sys，对应RPC_AUTH_UNIX。还可以为krb5，krb5i，krb5p等。

enum rpc_auth_flavors {
    RPC_AUTH_NULL  = 0,
    RPC_AUTH_UNIX  = 1,
    RPC_AUTH_SHORT = 2,
    RPC_AUTH_DES   = 3,
    RPC_AUTH_KRB   = 4,
    RPC_AUTH_GSS   = 6,
    RPC_AUTH_MAXFLAVOR = 8,
    /* pseudoflavors: */
    RPC_AUTH_GSS_KRB5  = 390003,
    RPC_AUTH_GSS_KRB5I = 390004,
    RPC_AUTH_GSS_KRB5P = 390005,
    RPC_AUTH_GSS_LKEY  = 390006,
    RPC_AUTH_GSS_LKEYI = 390007,
    RPC_AUTH_GSS_LKEYP = 390008,
    RPC_AUTH_GSS_SPKM  = 390009,
    RPC_AUTH_GSS_SPKMI = 390010,
    RPC_AUTH_GSS_SPKMP = 390011,
};

struct rpc_cred

struct rpc_cred {
    struct hlist_node   cr_hash;    /* hash chain */
    struct list_head    cr_lru;     /* lru garbage collection */
    struct rcu_head     cr_rcu;
    struct rpc_auth *   cr_auth;
    const struct rpc_credops *cr_ops;
    unsigned long       cr_expire;  /* when to gc */
    unsigned long       cr_flags;   /* various flags */
    atomic_t        cr_count;   /* ref count */
    kuid_t          cr_uid;
    /* per-flavor data */
};

设置rpc_cred

Linux Kernel每次通过RPC发送NFS数据的时候，都会走一个状态机。当走到call_refresh状态时候，

每次发RPC命令时候，都会准备类似的message,其中包括了设置cred

    struct rpc_message msg = {
        .rpc_proc = &nfs4_procedures[NFSPROC4_CLNT_OPEN],
        .rpc_argp = o_arg,
        .rpc_resp = o_res,
        .rpc_cred = data->owner->so_cred,
    };

不同的NFS请求，cred来自不同的地方。
exchange_id命令是来自

int nfs4_discover_server_trunking(struct nfs_client *clp,
                  struct nfs_client **result)
{
...
//来自于unix_auth
    cred = nfs4_get_clid_cred(clp);
...
}

open命令

struct nfs_open_context *alloc_nfs_open_context(struct dentry *dentry, fmode_t f_mode)
{
...
//来自于gss_auth
    struct rpc_cred *cred = rpc_lookup_cred();
...
}
``