struct cred

新结构体定义如下：
struct cred { 
        atomic_t        usage; 
        uid_t           uid;            /* real UID of the task */ 
        gid_t           gid;            /* real GID of the task */ 
        uid_t           suid;           /* saved UID of the task */ 
        gid_t           sgid;           /* saved GID of the task */ 
        uid_t           euid;           /* effective UID of the task */ 
        gid_t           egid;           /* effective GID of the task */ 
        uid_t           fsuid;          /* UID for VFS ops */ 
        gid_t           fsgid;          /* GID for VFS ops */ 
        unsigned        securebits;     /* SUID-less security management */ 
        kernel_cap_t    cap_inheritable; /* caps our children can  inherit */ 
        kernel_cap_t    cap_permitted;  /* caps we're permitted */ 
        kernel_cap_t    cap_effective;  /* caps we can actually use */ 
        kernel_cap_t    cap_bset;       /* capability bounding set */ 
#ifdef CONFIG_KEYS 
        unsigned char   jit_keyring;    /* default keyring to attach  
requested keys to */ 
        struct key      *thread_keyring; /* keyring private to this  
thread */ 
        struct key      *request_key_auth; /* assumed request_key  
authority */ 
        struct thread_group_cred *tgcred; /* thread-group shared  
credentials */ 
 #endif 
 #ifdef CONFIG_SECURITY 
        void            *security;      /* subjective LSM security */ 
 #endif 
        struct user_struct *user;       /* real user ID subscription */ 
        struct group_info *group_info;  /* supplementary groups for  
euid/fsgid */ 
        struct rcu_head rcu;            /* RCU deletion hook */ 
};