• Arnaldo Carvalho de Melo's avatar
    [XFRM]: Pack struct xfrm_policy · 46ca5f5d
    Arnaldo Carvalho de Melo authored
    [acme@newtoy net-2.6.20]$ pahole net/ipv4/tcp.o xfrm_policy
    /* /pub/scm/linux/kernel/git/acme/net-2.6.20/include/linux/security.h:67 */
    struct xfrm_policy {
            struct xfrm_policy *       next;                 /*     0     4 */
            struct hlist_node          bydst;                /*     4     8 */
            struct hlist_node          byidx;                /*    12     8 */
            rwlock_t                   lock;                 /*    20    36 */
            atomic_t                   refcnt;               /*    56     4 */
            struct timer_list          timer;                /*    60    24 */
            u8                         type;                 /*    84     1 */
    
            /* XXX 3 bytes hole, try to pack */
    
            u32                        priority;             /*    88     4 */
            u32                        index;                /*    92     4 */
            struct xfrm_selector       selector;             /*    96    56 */
            struct xfrm_lifetime_cfg   lft;                  /*   152    64 */
            struct xfrm_lifetime_cur   curlft;               /*   216    32 */
            struct dst_entry *         bundles;              /*   248     4 */
            __u16                      family;               /*   252     2 */
            __u8                       action;               /*   254     1 */
            __u8                       flags;                /*   255     1 */
            __u8                       dead;                 /*   256     1 */
            __u8                       xfrm_nr;              /*   257     1 */
    
            /* XXX 2 bytes hole, try to pack */
    
            struct xfrm_sec_ctx *      security;             /*   260     4 */
            struct xfrm_tmpl           xfrm_vec[6];          /*   264   360 */
    }; /* size: 624, sum members: 619, holes: 2, sum holes: 5 */
    
    So lets have just one hole instead of two, by moving 'type' to just before 'action',
    end result:
    
    [acme@newtoy net-2.6.20]$ codiff -s /tmp/tcp.o.before net/ipv4/tcp.o
    /pub/scm/linux/kernel/git/acme/net-2.6.20/net/ipv4/tcp.c:
      struct xfrm_policy |   -4
     1 struct changed
    [acme@newtoy net-2.6.20]$
    
    [acme@newtoy net-2.6.20]$ pahole -c 64 net/ipv4/tcp.o xfrm_policy
    /* /pub/scm/linux/kernel/git/acme/net-2.6.20/include/linux/security.h:67 */
    struct xfrm_policy {
            struct xfrm_policy *       next;                 /*     0     4 */
            struct hlist_node          bydst;                /*     4     8 */
            struct hlist_node          byidx;                /*    12     8 */
            rwlock_t                   lock;                 /*    20    36 */
            atomic_t                   refcnt;               /*    56     4 */
            struct timer_list          timer;                /*    60    24 */
            u32                        priority;             /*    84     4 */
            u32                        index;                /*    88     4 */
            struct xfrm_selector       selector;             /*    92    56 */
            struct xfrm_lifetime_cfg   lft;                  /*   148    64 */
            struct xfrm_lifetime_cur   curlft;               /*   212    32 */
            struct dst_entry *         bundles;              /*   244     4 */
            u16                        family;               /*   248     2 */
            u8                         type;                 /*   250     1 */
            u8                         action;               /*   251     1 */
            u8                         flags;                /*   252     1 */
            u8                         dead;                 /*   253     1 */
            u8                         xfrm_nr;              /*   254     1 */
    
            /* XXX 1 byte hole, try to pack */
    
            struct xfrm_sec_ctx *      security;             /*   256     4 */
            struct xfrm_tmpl           xfrm_vec[6];          /*   260   360 */
    }; /* size: 620, sum members: 619, holes: 1, sum holes: 1 */
    
    Are there any fugly data dependencies here? None that I know.
    
    In the process changed the removed the __ prefixed types, that are just for
    userspace visible headers.
    Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@mandriva.com>
    46ca5f5d
xfrm.h 28.6 KB