Kernel Arch. Solaris 7 vs. Solaris 8

I am reading the book Solaris Internals 1st edition where majority covers Solaris 7. I maintain this blog post as a place to show the differences I have found along the way.

Solaris 7 data structure for an address space object:

struct as {
        kmutex_t a_contents;    /* protect certain fields in the structure */
        uchar_t  a_flags;       /* as attributes */
        uchar_t a_vbits;        /* used for collecting statistics */
        kcondvar_t a_cv;        /* used by as_rangelock */
        struct  hat *a_hat;     /* hat structure */
        struct  hrmstat *a_hrm; /* ref and mod bits */
        caddr_t a_userlimit;    /* highest allowable address in this as */
        union {
                struct seg *seglast;    /* last segment hit on the addr space */
                ssl_spath *spath;       /* last search path in seg skiplist */
        } a_cache;
        krwlock_t a_lock;       /* protects fields below + a_cache */
        int     a_nwpage;       /* number of watched pages */
        struct watched_page *a_wpage;   /* list of watched pages (procfs) */
        seg_next a_segs;        /* segments in this address space. */
        size_t  a_size;         /* size of address space */
        struct  seg *a_tail;    /* last element in the segment list. */
        uint_t  a_nsegs;        /* number of elements in segment list */
        uchar_t a_lrep;         /* representation of a_segs: see #defines */
        uchar_t a_hilevel;      /* highest level in the a_segs skiplist */
        uchar_t a_unused;
        uchar_t a_updatedir;    /* mappings changed, rebuild as_objectdir */
        vnode_t **a_objectdir;  /* object directory (procfs) */
        size_t  a_sizedir;      /* size of object directory */
};

Solaris 8:

struct as {
        kmutex_t a_contents;    /* protect certain fields in the structure */
        uchar_t  a_flags;       /* as attributes */
        uchar_t a_vbits;        /* used for collecting statistics */
        kcondvar_t a_cv;        /* used by as_rangelock */
        struct  hat *a_hat;     /* hat structure */
        struct  hrmstat *a_hrm; /* ref and mod bits */
        caddr_t a_userlimit;    /* highest allowable address in this as */
        union {
                struct seg *seglast;    /* last segment hit on the addr space */
                ssl_spath *spath;       /* last search path in seg skiplist */
        } a_cache;
        krwlock_t a_lock;       /* protects fields below + a_cache */
        int     a_nwpage;       /* number of watched pages */
        struct watched_page *a_wpage;   /* list of watched pages (procfs) */
        seg_next a_segs;        /* segments in this address space. */
        size_t  a_size;         /* size of address space */
        struct  seg *a_tail;    /* last element in the segment list. */
        uint_t  a_nsegs;        /* number of elements in segment list */
        uchar_t a_lrep;         /* representation of a_segs: see #defines */
        uchar_t a_hilevel;      /* highest level in the a_segs skiplist */
        uchar_t a_unused;
        uchar_t a_updatedir;    /* mappings changed, rebuild as_objectdir */
        vnode_t **a_objectdir;  /* object directory (procfs) */
        size_t  a_sizedir;      /* size of object directory */
        struct as_callback *a_callbacks; /* callback list */
};

Looks we have an extra callback structure in Solaris 8. Wonder what this is all about?

/*
 * The as_callback is the basic structure which supports the ability to
 * inform clients of specific events pertaining to address space management.
 * An example of the need for this is a driver which has done long-term
 * locking of memory.  Address space management operations (events) such
 * as as_free, as_umap, and as_setprot will block indefinitely until the
 * pertinent memory is unlocked.  The callback mechanism provides the
 * way to inform the driver of the event so that the driver may do the
 * necessary unlocking.
 *
 * The contents of this structure is protected by a_contents lock
 */
typedef void (*callback_func_t)(struct as *, void *, uint_t);
struct as_callback {
        struct as_callback      *ascb_next;             /* list link */
        int                     ascb_refcnt;            /* reference count   */
        uint_t                  ascb_events;            /* event types */
        callback_func_t         ascb_func;              /* callback function */
        void                    *ascb_arg;              /* callback argument */
        caddr_t                 ascb_saddr;             /* start address */
        size_t                  ascb_len;               /* address range */
};