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#include <asm/interrupt.h>
#include <errno.h>
#include <kernel/con.h>
#include <kernel/fs.h>
#include <stdint.h>
#include <string.h>
/* memory dedicated to the block cache */
/* TODO: start buffers at kernel end not 512K */
#define BSTART 0x80000
#define BEND 0xA0000
static struct buffer *lru;
static struct buffer *mru;
struct buffer *buffer_get_block(uint16_t device, uint16_t block) {
struct buffer **p = &mru;
struct buffer *b;
if(!device)
return NULL;
/* check if the requested block is already in the cache */
while(b = *p) {
if(b->b_device != device || b->b_block != block)
goto next;
/* remove the buffer from the list */
if(lru == b && b->b_next) lru = b->b_next;
if(b->b_next) b->b_next->b_prev = b->b_prev;
if(b->b_prev) b->b_prev->b_next = b->b_next;
/* put the buffer back at the MRU end of the list */
b->b_next = NULL;
b->b_prev = mru;
if(mru != b)
mru->b_next = b;
mru = b;
cli();
/* if the buffer exists but isn't populated. wait on it */
if(!b->b_present) {
sleep_on(&b->b_wait);
printk("[buf] Waiting for buffer %04x:%04x to be populated...\n", b->b_device, b->b_block);
}
sti();
printk("[buf] Fetched block %04x:%04x from cache\n", b->b_device, b->b_block);
return b->b_device ? b : NULL;
next:
p = &b->b_prev;
}
/*
* otherwise, iterate through the least recently used
* buffers, to find a buffer that isn't pending an
* I/O operation, and read into it.
*/
p = &lru;
while(b = *p) {
if(b->b_present || !b->b_device)
break;
p = &(*p)->b_next;
}
if(!b)
return NULL;
b->b_device = device;
b->b_block = block;
b->b_present = 0;
block_read(b);
wake_up(&b->b_wait);
printk("[buf] Called driver to read block %04x:%04x\n", b->b_device, b->b_block);
return b->b_device ? b : NULL;
}
void buffer_init(void) {
int c = 0;
struct buffer *last = NULL;
struct buffer *b = (struct buffer*) BSTART;
void *d = (void*) (BEND - BLOCK_SIZE);
while(d > (void*) b) {
memset(b, 0, sizeof(struct buffer));
b->b_data = d;
b->b_prev = last;
if(last)
last->b_next = b;
last = b;
b = (struct buffer*) ((void*) b + sizeof(struct buffer));
d = (void*) (d - (void*) BLOCK_SIZE);
c++;
}
lru = (struct buffer*) BSTART;
mru = last;
printk("[buf] Buffers initialized (0x%x buffers in pool)\n", c);
}
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