1 #include <algorithm> 2 3 #include "flexpage.h" 4 5 6 7 /* Reset the flexpage using 'offset', being the file offset. */ 8 9 void Flexpage::reset(offset_t offset) 10 { 11 _counter = 0; 12 13 /* By definition (see "Flexible-Sized Page Objects - Object-Orientation 14 in Operation Systems"), flexpages are aligned to multiples of their 15 size. 16 17 The size of the flexpage depends on the amount of space around the 18 accessed page. It cannot exceed the size of the memory region. */ 19 20 size = max_multiple(region->start, region->end, PAGE_SIZE); 21 22 /* The base address of the flexpage is computed from the region start 23 and flexpage size. It will be no lower than the region start. 24 25 Sent flexpages may use higher bases due to receive window constraints, 26 these being communicated by the "hot spot". */ 27 28 base_addr = round(region->start, size); 29 30 /* Get the file offset for the base of the flexpage. This will be a 31 multiple of the flexpage size for alignment purposes. */ 32 33 base_offset = trunc(offset, size); 34 35 /* The page being accessed is relative to the base. 36 (This is transient information recording the initialising access 37 details.) */ 38 39 page_offset = trunc(offset - base_offset, PAGE_SIZE); 40 page_addr = base_addr + page_offset; 41 } 42 43 bool Flexpage::decrement() 44 { 45 if (_counter) 46 { 47 _counter--; 48 return _counter == 0; 49 } 50 else 51 return 0; 52 } 53 54 void Flexpage::increment() 55 { 56 _counter++; 57 } 58 59 void Flexpage::invalidate() 60 { 61 _counter = 0; 62 } 63 64 bool Flexpage::valid() 65 { 66 return _counter != 0; 67 } 68 69 /* Return whether the flexpage supports the given file 'position'. */ 70 71 bool Flexpage::supports_position(offset_t position) 72 { 73 return (base_offset <= position) && (position < (base_offset + size)); 74 } 75 76 void Flexpage::upgrade(flags_t flags) 77 { 78 if (flags && (flags != _flags)) 79 _flags |= flags; 80 } 81 82 /* Return a "send" flexpage for an access to 'offset' by positioning it relative 83 to 'hot_spot' for the receive flexpage window. */ 84 85 SendFlexpage Flexpage::to_send(offset_t offset, offset_t hot_spot, offset_t max_offset) 86 { 87 /* The dataspace offset of the flexpage base is a multiple of the flexpage 88 size. */ 89 90 offset_t receive_base_offset = trunc(offset, size); 91 92 /* The offset of the accessed page within the flexpage is constrained by the 93 current flexpage size. */ 94 95 offset_t page_offset = trunc(offset - receive_base_offset, PAGE_SIZE); 96 97 /* The receive flexpage offset (hot spot) must be constrained to the 98 flexpage, both the size and the start. */ 99 100 offset_t receive_size; 101 102 if (max_offset) 103 { 104 receive_size = trunc_multiple(max_offset - receive_base_offset, PAGE_SIZE); 105 receive_size = std::min(size, receive_size); 106 } 107 else 108 receive_size = size; 109 110 if (!receive_size) 111 return SendFlexpage(base_addr, page_order(0), _flags); 112 113 offset_t receive_page_offset = hot_spot % receive_size; 114 115 while ((receive_size > PAGE_SIZE) && (receive_page_offset != page_offset)) 116 { 117 receive_size /= 2; 118 receive_page_offset = hot_spot % receive_size; 119 } 120 121 /* The flexpage base address is adjusted using the difference in page 122 offsets. Where the receive flexpage offset is constained further, the 123 base address will be raised to become closer to the accessed page. */ 124 125 offset_t adjustment = page_offset - receive_page_offset; 126 127 return SendFlexpage(base_addr + adjustment, page_order(receive_size), _flags); 128 } 129 130 /* Return a representation of the flexpage for unmapping. */ 131 132 SendFlexpage Flexpage::to_unmap() 133 { 134 return SendFlexpage(base_addr, page_order(size), _flags); 135 } 136 137 // vim: tabstop=4 expandtab shiftwidth=4