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#include "types.h"
#include "param.h"
#include "x86.h"
#include "mmu.h"
#include "proc.h"
#include "defs.h"
#include "spinlock.h"
#include "buf.h"
struct buf buf[NBUF];
struct spinlock buf_table_lock;
// linked list of all buffers, through prev/next.
// bufhead->next is most recently used.
// bufhead->tail is least recently used.
struct buf bufhead;
void
binit(void)
{
struct buf *b;
initlock(&buf_table_lock, "buf_table");
bufhead.prev = &bufhead;
bufhead.next = &bufhead;
for(b = buf; b < buf+NBUF; b++){
b->next = bufhead.next;
b->prev = &bufhead;
bufhead.next->prev = b;
bufhead.next = b;
}
}
struct buf *
getblk(uint dev, uint sector)
{
struct buf *b;
acquire(&buf_table_lock);
while(1){
for(b = bufhead.next; b != &bufhead; b = b->next)
if((b->flags & (B_BUSY|B_VALID)) && b->dev == dev && b->sector == sector)
break;
if(b != &bufhead){
if(b->flags & B_BUSY){
sleep(buf, &buf_table_lock);
} else {
b->flags |= B_BUSY;
release(&buf_table_lock);
return b;
}
} else {
for(b = bufhead.prev; b != &bufhead; b = b->prev){
if((b->flags & B_BUSY) == 0){
b->flags = B_BUSY;
b->dev = dev;
b->sector = sector;
release(&buf_table_lock);
return b;
}
}
panic("getblk: no buffers");
}
}
}
struct buf *
bread(uint dev, uint sector)
{
void *c;
struct buf *b;
extern struct spinlock ide_lock;
b = getblk(dev, sector);
if(b->flags & B_VALID)
return b;
acquire(&ide_lock);
c = ide_start_rw(dev & 0xff, sector, b->data, 1, 1);
sleep (c, &ide_lock);
ide_finish(c);
b->flags |= B_VALID;
release(&ide_lock);
return b;
}
void
bwrite(struct buf *b, uint sector)
{
void *c;
extern struct spinlock ide_lock;
acquire(&ide_lock);
c = ide_start_rw(b->dev & 0xff, sector, b->data, 1, 0);
sleep (c, &ide_lock);
ide_finish(c);
b->flags |= B_VALID;
release(&ide_lock);
}
void
brelse(struct buf *b)
{
if((b->flags & B_BUSY) == 0)
panic("brelse");
acquire(&buf_table_lock);
b->next->prev = b->prev;
b->prev->next = b->next;
b->next = bufhead.next;
b->prev = &bufhead;
bufhead.next->prev = b;
bufhead.next = b;
b->flags &= ~B_BUSY;
wakeup(buf);
release(&buf_table_lock);
}
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