FreeBSD/Linux Kernel Cross Reference
sys/powerpc/powerpc/mmu_if.m

     #-
     # Copyright (c) 2005 Peter Grehan
     # All rights reserved.
     #
     # Redistribution and use in source and binary forms, with or without
     # modification, are permitted provided that the following conditions
     # are met:
     # 1. Redistributions of source code must retain the above copyright
     #    notice, this list of conditions and the following disclaimer.
    # 2. Redistributions in binary form must reproduce the above copyright
    #    notice, this list of conditions and the following disclaimer in the
    #    documentation and/or other materials provided with the distribution.
    #
    # THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
    # ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    # ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
    # FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
    # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
    # OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
    # HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
    # OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    # SUCH DAMAGE.
    #
    # $FreeBSD: releng/9.2/sys/powerpc/powerpc/mmu_if.m 248814 2013-03-28 06:31:04Z kib $
    #
    
    #include <sys/param.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/systm.h>
    
    #include <vm/vm.h>
    #include <vm/vm_page.h>
    
    #include <machine/mmuvar.h>
    
    /**
     * @defgroup MMU mmu - KObj methods for PowerPC MMU implementations
     * @brief A set of methods required by all MMU implementations. These
     * are basically direct call-thru's from the pmap machine-dependent
     * code.
     * Thanks to Bruce M Simpson's pmap man pages for routine descriptions.
     *@{
     */
    
    INTERFACE mmu;
    
    #
    # Default implementations of some methods
    #
    CODE {
            static void mmu_null_copy(mmu_t mmu, pmap_t dst_pmap, pmap_t src_pmap,
                vm_offset_t dst_addr, vm_size_t len, vm_offset_t src_addr)
            {
                    return;
            }
    
            static void mmu_null_growkernel(mmu_t mmu, vm_offset_t addr)
            {
                    return;
            }
    
            static void mmu_null_init(mmu_t mmu)
            {
                    return;
            }
    
            static boolean_t mmu_null_is_prefaultable(mmu_t mmu, pmap_t pmap,
                vm_offset_t va)
            {
                    return (FALSE);
            }
    
            static void mmu_null_object_init_pt(mmu_t mmu, pmap_t pmap,
                vm_offset_t addr, vm_object_t object, vm_pindex_t index,
                vm_size_t size)
            {
                    return;
            }
    
            static void mmu_null_page_init(mmu_t mmu, vm_page_t m)
            {
                    return;
            }
    
            static void mmu_null_remove_pages(mmu_t mmu, pmap_t pmap)
            {
                    return;
            }
    
            static int mmu_null_mincore(mmu_t mmu, pmap_t pmap, vm_offset_t addr,
                vm_paddr_t *locked_pa)
            {
                    return (0);
            }
    
            static void mmu_null_deactivate(struct thread *td)
           {
                   return;
           }
   
           static void mmu_null_align_superpage(mmu_t mmu, vm_object_t object,
               vm_ooffset_t offset, vm_offset_t *addr, vm_size_t size)
           {
                   return;
           }
   
           static struct pmap_md *mmu_null_scan_md(mmu_t mmu, struct pmap_md *p)
           {
                   return (NULL);
           }
   
           static void *mmu_null_mapdev_attr(mmu_t mmu, vm_offset_t pa,
               vm_size_t size, vm_memattr_t ma)
           {
                   return MMU_MAPDEV(mmu, pa, size);
           }
   
           static void mmu_null_kenter_attr(mmu_t mmu, vm_offset_t va,
               vm_offset_t pa, vm_memattr_t ma)
           {
                   MMU_KENTER(mmu, va, pa);
           }
   
           static void mmu_null_page_set_memattr(mmu_t mmu, vm_page_t m,
               vm_memattr_t ma)
           {
                   return;
           }
   };
   
   
   /**
    * @brief Change the wiring attribute for the page in the given physical
    * map and virtual address.
    *
    * @param _pmap         physical map of page
    * @param _va           page virtual address
    * @param _wired        TRUE to increment wired count, FALSE to decrement
    */
   METHOD void change_wiring {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _va;
           boolean_t       _wired;
   };
   
   
   /**
    * @brief Clear the 'modified' bit on the given physical page
    *
    * @param _pg           physical page
    */
   METHOD void clear_modify {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Clear the 'referenced' bit on the given physical page
    *
    * @param _pg           physical page
    */
   METHOD void clear_reference {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Clear the write and modified bits in each of the given
    * physical page's mappings
    *
    * @param _pg           physical page
    */
   METHOD void remove_write {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Copy the address range given by the source physical map, virtual
    * address and length to the destination physical map and virtual address.
    * This routine is optional (xxx default null implementation ?)
    *
    * @param _dst_pmap     destination physical map
    * @param _src_pmap     source physical map
    * @param _dst_addr     destination virtual address
    * @param _len          size of range
    * @param _src_addr     source virtual address
    */
   METHOD void copy {
           mmu_t           _mmu;
           pmap_t          _dst_pmap;
           pmap_t          _src_pmap;
           vm_offset_t     _dst_addr;
           vm_size_t       _len;
           vm_offset_t     _src_addr;
   } DEFAULT mmu_null_copy;
   
   
   /**
    * @brief Copy the source physical page to the destination physical page
    *
    * @param _src          source physical page
    * @param _dst          destination physical page
    */
   METHOD void copy_page {
           mmu_t           _mmu;
           vm_page_t       _src;
           vm_page_t       _dst;
   };
   
   METHOD void copy_pages {
           mmu_t           _mmu;
           vm_page_t       *_ma;
           vm_offset_t     _a_offset;
           vm_page_t       *_mb;
           vm_offset_t     _b_offset;
           int             _xfersize;
   };
   
   /**
    * @brief Create a mapping between a virtual/physical address pair in the
    * passed physical map with the specified protection and wiring
    *
    * @param _pmap         physical map
    * @param _va           mapping virtual address
    * @param _p            mapping physical page
    * @param _prot         mapping page protection
    * @param _wired        TRUE if page will be wired
    */
   METHOD void enter {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _va;
           vm_page_t       _p;
           vm_prot_t       _prot;
           boolean_t       _wired;
   };
   
   
   /**
    * @brief Maps a sequence of resident pages belonging to the same object.
    *
    * @param _pmap         physical map
    * @param _start        virtual range start
    * @param _end          virtual range end
    * @param _m_start      physical page mapped at start
    * @param _prot         mapping page protection
    */
   METHOD void enter_object {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _start;
           vm_offset_t     _end;
           vm_page_t       _m_start;
           vm_prot_t       _prot;
   };
   
   
   /**
    * @brief A faster entry point for page mapping where it is possible
    * to short-circuit some of the tests in pmap_enter.
    *
    * @param _pmap         physical map (and also currently active pmap)
    * @param _va           mapping virtual address
    * @param _pg           mapping physical page
    * @param _prot         new page protection - used to see if page is exec.
    */
   METHOD void enter_quick {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _va;
           vm_page_t       _pg;
           vm_prot_t       _prot;
   };
   
   
   /**
    * @brief Reverse map the given virtual address, returning the physical
    * page associated with the address if a mapping exists.
    *
    * @param _pmap         physical map
    * @param _va           mapping virtual address
    *
    * @retval 0            No mapping found
    * @retval addr         The mapping physical address
    */
   METHOD vm_paddr_t extract {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _va;
   };
   
   
   /**
    * @brief Reverse map the given virtual address, returning the
    * physical page if found. The page must be held (by calling
    * vm_page_hold) if the page protection matches the given protection
    *
    * @param _pmap         physical map
    * @param _va           mapping virtual address
    * @param _prot         protection used to determine if physical page
    *                      should be locked
    *
    * @retval NULL         No mapping found
    * @retval page         Pointer to physical page. Held if protections match
    */
   METHOD vm_page_t extract_and_hold {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _va;
           vm_prot_t       _prot;
   };
   
   
   /**
    * @brief Increase kernel virtual address space to the given virtual address.
    * Not really required for PowerPC, so optional unless the MMU implementation
    * can use it.
    *
    * @param _va           new upper limit for kernel virtual address space
    */
   METHOD void growkernel {
           mmu_t           _mmu;
           vm_offset_t     _va;
   } DEFAULT mmu_null_growkernel;
   
   
   /**
    * @brief Called from vm_mem_init. Zone allocation is available at
    * this stage so a convenient time to create zones. This routine is
    * for MMU-implementation convenience and is optional.
    */
   METHOD void init {
           mmu_t           _mmu;
   } DEFAULT mmu_null_init;
   
   
   /**
    * @brief Return if the page has been marked by MMU hardware to have been
    * modified
    *
    * @param _pg           physical page to test
    *
    * @retval boolean      TRUE if page has been modified
    */
   METHOD boolean_t is_modified {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Return whether the specified virtual address is a candidate to be
    * prefaulted in. This routine is optional.
    *
    * @param _pmap         physical map
    * @param _va           virtual address to test
    *
    * @retval boolean      TRUE if the address is a candidate.
    */
   METHOD boolean_t is_prefaultable {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _va;
   } DEFAULT mmu_null_is_prefaultable;
   
   
   /**
    * @brief Return whether or not the specified physical page was referenced
    * in any physical maps.
    *
    * @params _pg          physical page
    *
    * @retval boolean      TRUE if page has been referenced
    */
   METHOD boolean_t is_referenced {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Return a count of referenced bits for a page, clearing those bits.
    * Not all referenced bits need to be cleared, but it is necessary that 0
    * only be returned when there are none set.
    *
    * @params _m           physical page
    *
    * @retval int          count of referenced bits
    */
   METHOD boolean_t ts_referenced {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Map the requested physical address range into kernel virtual
    * address space. The value in _virt is taken as a hint. The virtual
    * address of the range is returned, or NULL if the mapping could not
    * be created. The range can be direct-mapped if that is supported.
    *
    * @param *_virt        Hint for start virtual address, and also return
    *                      value
    * @param _start        physical address range start
    * @param _end          physical address range end
    * @param _prot         protection of range (currently ignored)
    *
    * @retval NULL         could not map the area
    * @retval addr, *_virt mapping start virtual address
    */
   METHOD vm_offset_t map {
           mmu_t           _mmu;
           vm_offset_t     *_virt;
           vm_paddr_t      _start;
           vm_paddr_t      _end;
           int             _prot;
   };
   
   
   /**
    * @brief Used to create a contiguous set of read-only mappings for a
    * given object to try and eliminate a cascade of on-demand faults as
    * the object is accessed sequentially. This routine is optional.
    *
    * @param _pmap         physical map
    * @param _addr         mapping start virtual address
    * @param _object       device-backed V.M. object to be mapped
    * @param _pindex       page-index within object of mapping start
    * @param _size         size in bytes of mapping
    */
   METHOD void object_init_pt {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _addr;
           vm_object_t     _object;
           vm_pindex_t     _pindex;
           vm_size_t       _size;
   } DEFAULT mmu_null_object_init_pt;
   
   
   /**
    * @brief Used to determine if the specified page has a mapping for the
    * given physical map, by scanning the list of reverse-mappings from the
    * page. The list is scanned to a maximum of 16 entries.
    *
    * @param _pmap         physical map
    * @param _pg           physical page
    *
    * @retval bool         TRUE if the physical map was found in the first 16
    *                      reverse-map list entries off the physical page.
    */
   METHOD boolean_t page_exists_quick {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Initialise the machine-dependent section of the physical page
    * data structure. This routine is optional.
    *
    * @param _pg           physical page
    */
   METHOD void page_init {
           mmu_t           _mmu;
           vm_page_t       _pg;
   } DEFAULT mmu_null_page_init;
   
   
   /**
    * @brief Count the number of managed mappings to the given physical
    * page that are wired.
    *
    * @param _pg           physical page
    *
    * @retval int          the number of wired, managed mappings to the
    *                      given physical page
    */
   METHOD int page_wired_mappings {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Initialise a physical map data structure
    *
    * @param _pmap         physical map
    */
   METHOD void pinit {
           mmu_t           _mmu;
           pmap_t          _pmap;
   };
   
   
   /**
    * @brief Initialise the physical map for process 0, the initial process
    * in the system.
    * XXX default to pinit ?
    *
    * @param _pmap         physical map
    */
   METHOD void pinit0 {
           mmu_t           _mmu;
           pmap_t          _pmap;
   };
   
   
   /**
    * @brief Set the protection for physical pages in the given virtual address
    * range to the given value.
    *
    * @param _pmap         physical map
    * @param _start        virtual range start
    * @param _end          virtual range end
    * @param _prot         new page protection
    */
   METHOD void protect {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _start;
           vm_offset_t     _end;
           vm_prot_t       _prot;
   };
   
   
   /**
    * @brief Create a mapping in kernel virtual address space for the given array
    * of wired physical pages.
    *
    * @param _start        mapping virtual address start
    * @param *_m           array of physical page pointers
    * @param _count        array elements
    */
   METHOD void qenter {
           mmu_t           _mmu;
           vm_offset_t     _start;
           vm_page_t       *_pg;
           int             _count;
   };
   
   
   /**
    * @brief Remove the temporary mappings created by qenter.
    *
    * @param _start        mapping virtual address start
    * @param _count        number of pages in mapping
    */
   METHOD void qremove {
           mmu_t           _mmu;
           vm_offset_t     _start;
           int             _count;
   };
   
   
   /**
    * @brief Release per-pmap resources, e.g. mutexes, allocated memory etc. There
    * should be no existing mappings for the physical map at this point
    *
    * @param _pmap         physical map
    */
   METHOD void release {
           mmu_t           _mmu;
           pmap_t          _pmap;
   };
   
   
   /**
    * @brief Remove all mappings in the given physical map for the start/end
    * virtual address range. The range will be page-aligned.
    *
    * @param _pmap         physical map
    * @param _start        mapping virtual address start
    * @param _end          mapping virtual address end
    */
   METHOD void remove {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _start;
           vm_offset_t     _end;
   };
   
   
   /**
    * @brief Traverse the reverse-map list off the given physical page and
    * remove all mappings. Clear the PGA_WRITEABLE attribute from the page.
    *
    * @param _pg           physical page
    */
   METHOD void remove_all {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Remove all mappings in the given start/end virtual address range
    * for the given physical map. Similar to the remove method, but it used
    * when tearing down all mappings in an address space. This method is
    * optional, since pmap_remove will be called for each valid vm_map in
    * the address space later.
    *
    * @param _pmap         physical map
    * @param _start        mapping virtual address start
    * @param _end          mapping virtual address end
    */
   METHOD void remove_pages {
           mmu_t           _mmu;
           pmap_t          _pmap;
   } DEFAULT mmu_null_remove_pages;
   
   
   /**
    * @brief Zero a physical page. It is not assumed that the page is mapped,
    * so a temporary (or direct) mapping may need to be used.
    *
    * @param _pg           physical page
    */
   METHOD void zero_page {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Zero a portion of a physical page, starting at a given offset and
    * for a given size (multiples of 512 bytes for 4k pages).
    *
    * @param _pg           physical page
    * @param _off          byte offset from start of page
    * @param _size         size of area to zero
    */
   METHOD void zero_page_area {
           mmu_t           _mmu;
           vm_page_t       _pg;
           int             _off;
           int             _size;
   };
   
   
   /**
    * @brief Called from the idle loop to zero pages. XXX I think locking
    * constraints might be different here compared to zero_page.
    *
    * @param _pg           physical page
    */
   METHOD void zero_page_idle {
           mmu_t           _mmu;
           vm_page_t       _pg;
   };
   
   
   /**
    * @brief Extract mincore(2) information from a mapping.
    *
    * @param _pmap         physical map
    * @param _addr         page virtual address
    * @param _locked_pa    page physical address
    *
    * @retval 0            no result
    * @retval non-zero     mincore(2) flag values
    */
   METHOD int mincore {
           mmu_t           _mmu;
           pmap_t          _pmap;
           vm_offset_t     _addr;
           vm_paddr_t      *_locked_pa;
   } DEFAULT mmu_null_mincore;
   
   
   /**
    * @brief Perform any operations required to allow a physical map to be used
    * before it's address space is accessed.
    *
    * @param _td           thread associated with physical map
    */
   METHOD void activate {
           mmu_t           _mmu;
           struct thread   *_td;
   };
   
   /**
    * @brief Perform any operations required to deactivate a physical map,
    * for instance as it is context-switched out.
    *
    * @param _td           thread associated with physical map
    */
   METHOD void deactivate {
           mmu_t           _mmu;
           struct thread   *_td;
   } DEFAULT mmu_null_deactivate;
   
   /**
    * @brief Return a hint for the best virtual address to map a tentative
    * virtual address range in a given VM object. The default is to just
    * return the given tentative start address.
    *
    * @param _obj          VM backing object
    * @param _offset       starting offset with the VM object
    * @param _addr         initial guess at virtual address
    * @param _size         size of virtual address range
    */
   METHOD void align_superpage {
           mmu_t           _mmu;
           vm_object_t     _obj;
           vm_ooffset_t    _offset;
           vm_offset_t     *_addr;
           vm_size_t       _size;
   } DEFAULT mmu_null_align_superpage;
   
   
   
   
   /**
    * INTERNAL INTERFACES
    */
   
   /**
    * @brief Bootstrap the VM system. At the completion of this routine, the
    * kernel will be running in it's own address space with full control over
    * paging.
    *
    * @param _start        start of reserved memory (obsolete ???)
    * @param _end          end of reserved memory (obsolete ???)
    *                      XXX I think the intent of these was to allow
    *                      the memory used by kernel text+data+bss and
    *                      loader variables/load-time kld's to be carved out
    *                      of available physical mem.
    *
    */
   METHOD void bootstrap {
           mmu_t           _mmu;
           vm_offset_t     _start;
           vm_offset_t     _end;
   };
   
   /**
    * @brief Set up the MMU on the current CPU. Only called by the PMAP layer
    * for alternate CPUs on SMP systems.
    *
    * @param _ap           Set to 1 if the CPU being set up is an AP
    *
    */
   METHOD void cpu_bootstrap {
           mmu_t           _mmu;
           int             _ap;
   };
   
   
   /**
    * @brief Create a kernel mapping for a given physical address range.
    * Called by bus code on behalf of device drivers. The mapping does not
    * have to be a virtual address: it can be a direct-mapped physical address
    * if that is supported by the MMU.
    *
    * @param _pa           start physical address
    * @param _size         size in bytes of mapping
    *
    * @retval addr         address of mapping.
    */
   METHOD void * mapdev {
           mmu_t           _mmu;
           vm_offset_t     _pa;
           vm_size_t       _size;
   };
   
   /**
    * @brief Create a kernel mapping for a given physical address range.
    * Called by bus code on behalf of device drivers. The mapping does not
    * have to be a virtual address: it can be a direct-mapped physical address
    * if that is supported by the MMU.
    *
    * @param _pa           start physical address
    * @param _size         size in bytes of mapping
    * @param _attr         cache attributes
    *
    * @retval addr         address of mapping.
    */
   METHOD void * mapdev_attr {
           mmu_t           _mmu;
           vm_offset_t     _pa;
           vm_size_t       _size;
           vm_memattr_t    _attr;
   } DEFAULT mmu_null_mapdev_attr;
   
   /**
    * @brief Change cache control attributes for a page. Should modify all
    * mappings for that page.
    *
    * @param _m            page to modify
    * @param _ma           new cache control attributes
    */
   METHOD void page_set_memattr {
           mmu_t           _mmu;
           vm_page_t       _pg;
           vm_memattr_t    _ma;
   } DEFAULT mmu_null_page_set_memattr;
   
   /**
    * @brief Remove the mapping created by mapdev. Called when a driver
    * is unloaded.
    *
    * @param _va           Mapping address returned from mapdev
    * @param _size         size in bytes of mapping
    */
   METHOD void unmapdev {
           mmu_t           _mmu;
           vm_offset_t     _va;
           vm_size_t       _size;
   };
   
   
   /**
    * @brief Reverse-map a kernel virtual address
    *
    * @param _va           kernel virtual address to reverse-map
    *
    * @retval pa           physical address corresponding to mapping
    */
   METHOD vm_offset_t kextract {
           mmu_t           _mmu;
           vm_offset_t     _va;
   };
   
   
   /**
    * @brief Map a wired page into kernel virtual address space
    *
    * @param _va           mapping virtual address
    * @param _pa           mapping physical address
    */
   METHOD void kenter {
           mmu_t           _mmu;
           vm_offset_t     _va;
           vm_offset_t     _pa;
   };
   
   /**
    * @brief Map a wired page into kernel virtual address space
    *
    * @param _va           mapping virtual address
    * @param _pa           mapping physical address
    * @param _ma           mapping cache control attributes
    */
   METHOD void kenter_attr {
           mmu_t           _mmu;
           vm_offset_t     _va;
           vm_offset_t     _pa;
           vm_memattr_t    _ma;
   } DEFAULT mmu_null_kenter_attr;
   
   /**
    * @brief Determine if the given physical address range has been direct-mapped.
    *
    * @param _pa           physical address start
    * @param _size         physical address range size
    *
    * @retval bool         TRUE if the range is direct-mapped.
    */
   METHOD boolean_t dev_direct_mapped {
           mmu_t           _mmu;
           vm_offset_t     _pa;
           vm_size_t       _size;
   };
   
   
   /**
    * @brief Enforce instruction cache coherency. Typically called after a
    * region of memory has been modified and before execution of or within
    * that region is attempted. Setting breakpoints in a process through
    * ptrace(2) is one example of when the instruction cache needs to be
    * made coherent.
    *
    * @param _pm           the physical map of the virtual address
    * @param _va           the virtual address of the modified region
    * @param _sz           the size of the modified region
    */
   METHOD void sync_icache {
           mmu_t           _mmu;
           pmap_t          _pm;
           vm_offset_t     _va;
           vm_size_t       _sz;
   };
   
   
   /**
    * @brief Create temporary memory mapping for use by dumpsys().
    *
    * @param _md           The memory chunk in which the mapping lies.
    * @param _ofs          The offset within the chunk of the mapping.
    * @param _sz           The requested size of the mapping.
    *
    * @retval vm_offset_t  The virtual address of the mapping.
    *                      
    * The sz argument is modified to reflect the actual size of the
    * mapping.
    */
   METHOD vm_offset_t dumpsys_map {
           mmu_t           _mmu;
           struct pmap_md  *_md;
           vm_size_t       _ofs;
           vm_size_t       *_sz;
   };
   
   
   /**
    * @brief Remove temporary dumpsys() mapping.
    *
    * @param _md           The memory chunk in which the mapping lies.
    * @param _ofs          The offset within the chunk of the mapping.
    * @param _va           The virtual address of the mapping.
    */
   METHOD void dumpsys_unmap {
           mmu_t           _mmu;
           struct pmap_md  *_md;
           vm_size_t       _ofs;
           vm_offset_t     _va;
   };
   
   
   /**
    * @brief Scan/iterate memory chunks.
    *
    * @param _prev         The previously returned chunk or NULL.
    *
    * @retval              The next (or first when _prev is NULL) chunk.
    */
   METHOD struct pmap_md * scan_md {
           mmu_t           _mmu;
           struct pmap_md  *_prev;
   } DEFAULT mmu_null_scan_md;

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