94 lines
3.0 KiB
C
94 lines
3.0 KiB
C
/* The file system maintains a buffer cache to reduce the number of disk
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* accesses needed. Whenever a read or write to the disk is done, a check is
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* first made to see if the block is in the cache. This file manages the
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* cache.
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*
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* The entry points into this file are:
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* get_block: request to fetch a block for reading or writing from cache
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* put_block: return a block previously requested with get_block
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* alloc_zone: allocate a new zone (to increase the length of a file)
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* free_zone: release a zone (when a file is removed)
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* invalidate: remove all the cache blocks on some device
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*
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* Private functions:
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* read_block: read or write a block from the disk itself
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*/
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#include "fs.h"
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#include <minix/u64.h>
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#include <minix/bdev.h>
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#include <sys/param.h>
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#include <stdlib.h>
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#include <assert.h>
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#include <minix/libminixfs.h>
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#include <math.h>
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#include "buf.h"
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#include "super.h"
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#include "inode.h"
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/*===========================================================================*
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* alloc_zone *
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*===========================================================================*/
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zone_t alloc_zone(
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dev_t dev, /* device where zone wanted */
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zone_t z /* try to allocate new zone near this one */
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)
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{
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/* Allocate a new zone on the indicated device and return its number. */
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bit_t b, bit;
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struct super_block *sp;
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static int print_oos_msg = 1;
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/* Note that the routine alloc_bit() returns 1 for the lowest possible
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* zone, which corresponds to sp->s_firstdatazone. To convert a value
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* between the bit number, 'b', used by alloc_bit() and the zone number, 'z',
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* stored in the inode, use the formula:
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* z = b + sp->s_firstdatazone - 1
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* Alloc_bit() never returns 0, since this is used for NO_BIT (failure).
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*/
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sp = get_super(dev);
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/* If z is 0, skip initial part of the map known to be fully in use. */
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if (z == sp->s_firstdatazone) {
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bit = sp->s_zsearch;
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} else {
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bit = (bit_t) (z - (sp->s_firstdatazone - 1));
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}
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b = alloc_bit(sp, ZMAP, bit);
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if (b == NO_BIT) {
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err_code = ENOSPC;
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if (print_oos_msg)
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printf("No space on device %d/%d\n", major(sp->s_dev),
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minor(sp->s_dev));
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print_oos_msg = 0; /* Don't repeat message */
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return(NO_ZONE);
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}
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print_oos_msg = 1;
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if (z == sp->s_firstdatazone) sp->s_zsearch = b; /* for next time */
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return( (zone_t) (sp->s_firstdatazone - 1) + (zone_t) b);
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}
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/*===========================================================================*
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* free_zone *
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*===========================================================================*/
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void free_zone(
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dev_t dev, /* device where zone located */
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zone_t numb /* zone to be returned */
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)
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{
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/* Return a zone. */
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register struct super_block *sp;
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bit_t bit;
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/* Locate the appropriate super_block and return bit. */
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sp = get_super(dev);
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if (numb < sp->s_firstdatazone || numb >= sp->s_zones) return;
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bit = (bit_t) (numb - (zone_t) (sp->s_firstdatazone - 1));
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free_bit(sp, ZMAP, bit);
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if (bit < sp->s_zsearch) sp->s_zsearch = bit;
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}
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