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/*
* 'buffer.c' implements the buffer-cache functions. Race-conditions have
* been avoided by NEVER letting a interrupt change a buffer (except for the
* data, of course), but instead letting the caller do it. NOTE! As interrupts
* can wake up a caller, some cli-sti sequences are needed to check for
* sleep-on-calls. These should be extremely quick, though (I hope).
*/
#include <linux/config.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <asm/system.h>
#if (BUFFER_END & 0xfff)
#error "Bad BUFFER_END value"
#endif
#if (BUFFER_END > 0xA0000 && BUFFER_END <= 0x100000)
#error "Bad BUFFER_END value"
#endif
extern int end;
struct buffer_head * start_buffer = (struct buffer_head *) &end;
struct buffer_head * hash_table[NR_HASH];
static struct buffer_head * free_list;
static struct task_struct * buffer_wait = NULL;
int NR_BUFFERS = 0;
static inline void wait_on_buffer(struct buffer_head * bh)
{
cli();
while (bh->b_lock)
sleep_on(&bh->b_wait);
sti();
}
int sys_sync(void)
{
int i;
struct buffer_head * bh;
sync_inodes(); /* write out inodes into buffers */
bh = start_buffer;
for (i=0 ; i<NR_BUFFERS ; i++,bh++) {
wait_on_buffer(bh);
if (bh->b_dirt)
ll_rw_block(WRITE,bh);
}
return 0;
}
static int sync_dev(int dev)
{
int i;
struct buffer_head * bh;
bh = start_buffer;
for (i=0 ; i<NR_BUFFERS ; i++,bh++) {
if (bh->b_dev != dev)
continue;
wait_on_buffer(bh);
if (bh->b_dirt)
ll_rw_block(WRITE,bh);
}
return 0;
}
#define _hashfn(dev,block) (((unsigned)(dev^block))%NR_HASH)
#define hash(dev,block) hash_table[_hashfn(dev,block)]
static inline void remove_from_queues(struct buffer_head * bh)
{
/* remove from hash-queue */
if (bh->b_next)
bh->b_next->b_prev = bh->b_prev;
if (bh->b_prev)
bh->b_prev->b_next = bh->b_next;
if (hash(bh->b_dev,bh->b_blocknr) == bh)
hash(bh->b_dev,bh->b_blocknr) = bh->b_next;
/* remove from free list */
if (!(bh->b_prev_free) || !(bh->b_next_free))
panic("Free block list corrupted");
bh->b_prev_free->b_next_free = bh->b_next_free;
bh->b_next_free->b_prev_free = bh->b_prev_free;
if (free_list == bh)
free_list = bh->b_next_free;
}
static inline void insert_into_queues(struct buffer_head * bh)
{
/* put at end of free list */
bh->b_next_free = free_list;
bh->b_prev_free = free_list->b_prev_free;
free_list->b_prev_free->b_next_free = bh;
free_list->b_prev_free = bh;
/* put the buffer in new hash-queue if it has a device */
bh->b_prev = NULL;
bh->b_next = NULL;
if (!bh->b_dev)
return;
bh->b_next = hash(bh->b_dev,bh->b_blocknr);
hash(bh->b_dev,bh->b_blocknr) = bh;
bh->b_next->b_prev = bh;
}
static struct buffer_head * find_buffer(int dev, int block)
{
struct buffer_head * tmp;
for (tmp = hash(dev,block) ; tmp != NULL ; tmp = tmp->b_next)
if (tmp->b_dev==dev && tmp->b_blocknr==block)
return tmp;
return NULL;
}
/*
* Why like this, I hear you say... The reason is race-conditions.
* As we don't lock buffers (unless we are readint them, that is),
* something might happen to it while we sleep (ie a read-error
* will force it bad). This shouldn't really happen currently, but
* the code is ready.
*/
struct buffer_head * get_hash_table(int dev, int block)
{
struct buffer_head * bh;
repeat:
if (!(bh=find_buffer(dev,block)))
return NULL;
bh->b_count++;
wait_on_buffer(bh);
if (bh->b_dev != dev || bh->b_blocknr != block) {
brelse(bh);
goto repeat;
}
return bh;
}
/*
* Ok, this is getblk, and it isn't very clear, again to hinder
* race-conditions. Most of the code is seldom used, (ie repeating),
* so it should be much more efficient than it looks.
*/
struct buffer_head * getblk(int dev,int block)
{
struct buffer_head * tmp;
repeat:
if (tmp=get_hash_table(dev,block))
return tmp;
tmp = free_list;
do {
if (!tmp->b_count) {
wait_on_buffer(tmp); /* we still have to wait */
if (!tmp->b_count) /* on it, it might be dirty */
break;
}
tmp = tmp->b_next_free;
} while (tmp != free_list || (tmp=NULL));
/* Kids, don't try THIS at home ^^^^^. Magic */
if (!tmp) {
printk("Sleeping on free buffer ..");
sleep_on(&buffer_wait);
printk("ok\n");
goto repeat;
}
tmp->b_count++;
remove_from_queues(tmp);
/*
* Now, when we know nobody can get to this node (as it's removed from the
* free list), we write it out. We can sleep here without fear of race-
* conditions.
*/
if (tmp->b_dirt)
sync_dev(tmp->b_dev);
/* update buffer contents */
tmp->b_dev=dev;
tmp->b_blocknr=block;
tmp->b_dirt=0;
tmp->b_uptodate=0;
/* NOTE!! While we possibly slept in sync_dev(), somebody else might have
* added "this" block already, so check for that. Thank God for goto's.
*/
if (find_buffer(dev,block)) {
tmp->b_dev=0; /* ok, someone else has beaten us */
tmp->b_blocknr=0; /* to it - free this block and */
tmp->b_count=0; /* try again */
insert_into_queues(tmp);
goto repeat;
}
/* and then insert into correct position */
insert_into_queues(tmp);
return tmp;
}
void brelse(struct buffer_head * buf)
{
if (!buf)
return;
wait_on_buffer(buf);
if (!(buf->b_count--))
panic("Trying to free free buffer");
wake_up(&buffer_wait);
}
/*
* bread() reads a specified block and returns the buffer that contains
* it. It returns NULL if the block was unreadable.
*/
struct buffer_head * bread(int dev,int block)
{
struct buffer_head * bh;
if (!(bh=getblk(dev,block)))
panic("bread: getblk returned NULL\n");
if (bh->b_uptodate)
return bh;
ll_rw_block(READ,bh);
if (bh->b_uptodate)
return bh;
brelse(bh);
return (NULL);
}
void buffer_init(void)
{
struct buffer_head * h = start_buffer;
void * b = (void *) BUFFER_END;
int i;
while ( (b -= BLOCK_SIZE) >= ((void *) (h+1)) ) {
h->b_dev = 0;
h->b_dirt = 0;
h->b_count = 0;
h->b_lock = 0;
h->b_uptodate = 0;
h->b_wait = NULL;
h->b_next = NULL;
h->b_prev = NULL;
h->b_data = (char *) b;
h->b_prev_free = h-1;
h->b_next_free = h+1;
h++;
NR_BUFFERS++;
if (b == (void *) 0x100000)
b = (void *) 0xA0000;
}
h--;
free_list = start_buffer;
free_list->b_prev_free = h;
h->b_next_free = free_list;
for (i=0;i<NR_HASH;i++)
hash_table[i]=NULL;
}
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