mirror of
https://github.com/xcat2/xNBA.git
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Modified to use physical addresses, and to not assume that we can directly
refer to data outside of our data or stack segments.
This commit is contained in:
parent
e3f2aa7b4d
commit
e75b7480d0
@ -18,114 +18,127 @@
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#include "stddef.h"
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#include "string.h"
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#include "io.h"
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#include "buffer.h"
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/*
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* Split a free block at the specified address, to produce two
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* consecutive free blocks. If the address is not within the free
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* block, do nothing and return success. If one of the resulting free
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* blocks would be too small to contain the free block descriptor,
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* return failure.
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*
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*/
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static int split_free_block ( struct buffer_free_block *block, void *split ) {
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struct buffer_free_block *new_block = split;
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if ( ( split <= ( void * ) block ) || ( split >= block->end ) ) {
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/* Split is outside block; nothing to do */
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return 1;
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}
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if ( ( ( block + 1 ) > new_block ) ||
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( ( ( void * ) ( new_block + 1 ) ) > block->end ) ) {
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/* Split block would be too small; fail */
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return 0;
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}
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/* Create new block, link into free list */
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new_block->next = block->next;
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new_block->next->prev = new_block;
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new_block->prev = block->prev;
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new_block->end = block->end;
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block->next = new_block;
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block->end = new_block;
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return 1;
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}
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/*
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* Remove a block from the free list.
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*
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* Note that this leaves block->next intact.
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*
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*/
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static inline void unfree_block ( struct buffer_free_block *block ) {
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block->prev->next = block->next;
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block->next->prev = block->prev;
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}
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/*
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* Mark a stretch of memory within a buffer as allocated.
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*
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*/
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static inline int mark_allocated ( struct buffer *buffer,
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void *start, void *end ) {
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struct buffer_free_block *block = buffer->free_blocks.next;
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while ( block != &buffer->free_blocks ) {
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if ( ! ( split_free_block ( block, start ) &&
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split_free_block ( block, end ) ) ) {
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/* Block split failure; fail */
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return 0;
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}
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/* At this point, block can be entirely contained
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* within [start,end), but it can't overlap.
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*/
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if ( ( ( ( void * ) block ) >= start ) &&
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( ( ( void * ) block ) < end ) ) {
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unfree_block ( block );
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}
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block = block->next;
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}
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return 1;
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}
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/*
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* Place data into a buffer
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*
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*/
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int fill_buffer ( struct buffer *buffer, void *data,
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off_t offset, size_t len ) {
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void *start = buffer->start + offset;
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void *end = start + len;
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if ( ! mark_allocated ( buffer, start, end ) ) {
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/* Allocation failure; fail */
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return 0;
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}
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memcpy ( start, data, len );
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return 1;
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}
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/*
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* Initialise a buffer
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*
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*/
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static void init_buffer ( struct buffer *buffer, void *start, size_t len ) {
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struct buffer_free_block *block;
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block = start;
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block->next = &buffer->free_blocks;
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block->prev = &buffer->free_blocks;
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block->end = start + len;
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buffer->free_blocks.next = block;
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buffer->free_blocks.prev = block;
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void init_buffer ( struct buffer *buffer, physaddr_t start, size_t len ) {
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buffer->start = start;
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buffer->end = start + len;
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buffer->first_free = start;
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if ( len ) {
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char tail = 1;
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copy_to_phys ( start, &tail, sizeof ( tail ) );
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}
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}
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/*
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* Move a buffer
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* Split a free block
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*
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*/
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static void split_free_block ( struct buffer_free_block *desc,
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physaddr_t block, physaddr_t split ) {
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/* If split point is before start of block, do nothing */
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if ( split <= block )
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return;
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/* If split point is after end of block, do nothing */
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if ( split >= desc->end )
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return;
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/* Create descriptor for new free block */
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copy_to_phys ( split, &desc->tail, sizeof ( desc->tail ) );
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if ( ! desc->tail )
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copy_to_phys ( split, desc, sizeof ( *desc ) );
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/* Update descriptor for old free block */
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desc->tail = 0;
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desc->next_free = split;
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desc->end = split;
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copy_to_phys ( block, desc, sizeof ( *desc ) );
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}
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/*
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* Mark a free block as used
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*
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*/
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static inline void unfree_block ( struct buffer *buffer,
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struct buffer_free_block *desc,
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physaddr_t prev_block ) {
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struct buffer_free_block prev_desc;
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/* If this is the first block, just update first_free */
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if ( ! prev_block ) {
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buffer->first_free = desc->next_free;
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return;
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}
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/* Get descriptor for previous block (which cannot be a tail block) */
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copy_from_phys ( &prev_desc, prev_block, sizeof ( prev_desc ) );
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/* Modify descriptor for previous block and write it back */
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prev_desc.next_free = desc->next_free;
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copy_to_phys ( prev_block, &prev_desc, sizeof ( prev_desc ) );
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}
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/*
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* Write data into a buffer
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*
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* It is the caller's responsibility to ensure that the boundaries
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* between data blocks are more than sizeof(struct buffer_free_block)
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* apart. If this condition is not satisfied, data corruption will
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* occur.
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*
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* Returns the offset to the first gap in the buffer. (When the
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* buffer is full, returns the offset to the byte past the end of the
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* buffer.)
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*
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*/
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off_t fill_buffer ( struct buffer *buffer, void *data,
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off_t offset, size_t len ) {
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struct buffer_free_block desc;
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physaddr_t block, prev_block;
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physaddr_t data_start, data_end;
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/* Calculate start and end addresses of data */
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data_start = buffer->start + offset;
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data_end = data_start + len;
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/* Iterate through the buffer's free blocks */
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prev_block = 0;
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block = buffer->first_free;
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while ( block < buffer->end ) {
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/* Read block descriptor */
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desc.next_free = buffer->end;
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desc.end = buffer->end;
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copy_from_phys ( &desc.tail, block, sizeof ( desc.tail ) );
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if ( ! desc.tail )
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copy_from_phys ( &desc, block, sizeof ( desc ) );
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/* Split block at data start and end markers */
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split_free_block ( &desc, block, data_start );
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split_free_block ( &desc, block, data_end );
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/* Block is now either completely contained by or
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* completely outside the data area
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*/
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if ( ( block >= data_start ) && ( block <= data_end ) ) {
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/* Block is within the data area */
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unfree_block ( buffer, &desc, prev_block );
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copy_to_phys ( block, data + ( block - data_start ),
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desc.end - block );
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} else {
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/* Block is outside the data area */
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prev_block = block;
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}
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/* Move to next free block */
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block = desc.next_free;
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}
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return ( buffer->first_free - buffer->start );
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}
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@ -1,16 +1,38 @@
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#ifndef BUFFER_H
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#define BUFFER_H
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#include "stdint.h"
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/*
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* Free blocks in the buffer start with a "tail byte". If non-zero,
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* this byte indicates that the free block is the tail of the buffer,
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* i.e. occupies all the remaining space up to the end of the buffer.
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* When the tail byte is non-zero, it indicates that the remainder of
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* the descriptor (the struct buffer_free_block) follows the tail
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* byte.
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*
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* This scheme is necessary because we may end up with a tail that is
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* smaller than a struct buffer_free_block.
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*
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*/
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struct buffer_free_block {
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struct buffer_free_block *next;
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struct buffer_free_block *prev;
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void *end;
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};
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char tail;
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physaddr_t next_free;
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physaddr_t end;
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} __attribute__ (( packed ));
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struct buffer {
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struct buffer_free_block free_blocks;
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void *start;
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void *end;
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physaddr_t start;
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physaddr_t end;
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physaddr_t first_free;
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};
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/* Functions in buffer.c */
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extern void init_buffer ( struct buffer *buffer, physaddr_t start,
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size_t len );
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extern off_t fill_buffer ( struct buffer *buffer, void *data,
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off_t offset, size_t len );
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#endif /* BUFFER_H */
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