Linux0.96c/fs/buffer.c
/*
* linux/fs/buffer.c
*
* (C) 1991 Linus Torvalds
*/
/*
* '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).
*/
/*
* NOTE! There is one discordant note here: checking floppies for
* disk change. This is where it fits best, I think, as it should
* invalidate changed floppy-disk-caches.
*/
#include <stdarg.h>
#include <linux/config.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <asm/system.h>
#include <asm/io.h>
extern int end;
static struct buffer_head * start_buffer = (struct buffer_head *) &end;
static 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();
}
static void sync_buffers(int dev)
{
int i;
struct buffer_head * bh;
bh = free_list;
for (i = NR_BUFFERS*2 ; i-- > 0 ; bh = bh->b_next_free) {
if (bh->b_lock)
continue;
if (!bh->b_dirt)
continue;
ll_rw_block(WRITE,bh);
}
}
int sys_sync(void)
{
int i;
for (i=0 ; i<NR_SUPER ; i++)
if (super_block[i].s_dev
&& super_block[i].s_op
&& super_block[i].s_op->write_super
&& super_block[i].s_dirt)
super_block[i].s_op->write_super(&super_block[i]);
sync_inodes(); /* write out inodes into buffers */
sync_buffers(0);
return 0;
}
int sync_dev(int dev)
{
struct super_block * sb;
if (sb = get_super (dev))
if (sb->s_op && sb->s_op->write_super && sb->s_dirt)
sb->s_op->write_super (sb);
sync_buffers(dev);
sync_inodes();
sync_buffers(dev);
return 0;
}
void inline invalidate_buffers(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_dev == dev)
bh->b_uptodate = bh->b_dirt = 0;
}
}
/*
* This routine checks whether a floppy has been changed, and
* invalidates all buffer-cache-entries in that case. This
* is a relatively slow routine, so we have to try to minimize using
* it. Thus it is called only upon a 'mount' or 'open'. This
* is the best way of combining speed and utility, I think.
* People changing diskettes in the middle of an operation deserve
* to loose :-)
*
* NOTE! Although currently this is only for floppies, the idea is
* that any additional removable block-device will use this routine,
* and that mount/open needn't know that floppies/whatever are
* special.
*/
void check_disk_change(int dev)
{
int i;
struct buffer_head * bh;
if (MAJOR(dev) != 2)
return;
if (!(bh = getblk(dev,0)))
return;
i = floppy_change(bh);
brelse(bh);
if (!i)
return;
for (i=0 ; i<NR_SUPER ; i++)
if (super_block[i].s_dev == dev)
put_super(super_block[i].s_dev);
invalidate_inodes(dev);
invalidate_buffers(dev);
}
#define _hashfn(dev,block) (((unsigned)(dev^block))%NR_HASH)
#define hash(dev,block) hash_table[_hashfn(dev,block)]
static inline void remove_from_hash_queue(struct buffer_head * bh)
{
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;
bh->b_next = bh->b_prev = NULL;
}
static inline void remove_from_free_list(struct buffer_head * bh)
{
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;
bh->b_next_free = bh->b_prev_free = NULL;
}
static inline void remove_from_queues(struct buffer_head * bh)
{
remove_from_hash_queue(bh);
remove_from_free_list(bh);
}
static inline void put_first_free(struct buffer_head * bh)
{
if (!bh || (bh == free_list))
return;
remove_from_free_list(bh);
/* add to front 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;
free_list = bh;
}
static inline void put_last_free(struct buffer_head * bh)
{
if (!bh)
return;
if (bh == free_list) {
free_list = bh->b_next_free;
return;
}
remove_from_free_list(bh);
/* add to back 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;
}
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;
if (bh->b_next)
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;
for (;;) {
if (!(bh=find_buffer(dev,block)))
return NULL;
bh->b_count++;
wait_on_buffer(bh);
if (bh->b_dev == dev && bh->b_blocknr == block) {
put_last_free(bh);
return bh;
}
bh->b_count--;
}
}
/*
* 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.
*
* The algoritm is changed: hopefully better, and an elusive bug removed.
*
* 14.02.92: changed it to sync dirty buffers a bit: better performance
* when the filesystem starts to get full of dirty blocks (I hope).
*/
#define BADNESS(bh) (((bh)->b_dirt<<1)+(bh)->b_lock)
struct buffer_head * getblk(int dev,int block)
{
struct buffer_head * bh, * tmp;
int buffers;
repeat:
if (bh = get_hash_table(dev,block))
return bh;
buffers = NR_BUFFERS;
for (tmp = free_list ; buffers-- > 0 ; tmp = tmp->b_next_free) {
if (tmp->b_count)
continue;
if (!bh || BADNESS(tmp)<BADNESS(bh)) {
bh = tmp;
if (!BADNESS(tmp))
break;
}
#if 0
if (tmp->b_dirt)
ll_rw_block(WRITEA,tmp);
#endif
}
/* and repeat until we find something good */
if (!bh) {
sleep_on(&buffer_wait);
goto repeat;
}
wait_on_buffer(bh);
if (bh->b_count)
goto repeat;
if (bh->b_dirt) {
sync_buffers(bh->b_dev);
goto repeat;
}
/* NOTE!! While we slept waiting for this block, somebody else might */
/* already have added "this" block to the cache. check it */
if (find_buffer(dev,block))
goto repeat;
/* OK, FINALLY we know that this buffer is the only one of it's kind, */
/* and that it's unused (b_count=0), unlocked (b_lock=0), and clean */
bh->b_count=1;
bh->b_dirt=0;
bh->b_uptodate=0;
remove_from_queues(bh);
bh->b_dev=dev;
bh->b_blocknr=block;
insert_into_queues(bh);
return bh;
}
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);
wait_on_buffer(bh);
if (bh->b_uptodate)
return bh;
brelse(bh);
return NULL;
}
#define COPYBLK(from,to) \
__asm__("cld\n\t" \
"rep\n\t" \
"movsl\n\t" \
::"c" (BLOCK_SIZE/4),"S" (from),"D" (to) \
:"cx","di","si")
/*
* bread_page reads four buffers into memory at the desired address. It's
* a function of its own, as there is some speed to be got by reading them
* all at the same time, not waiting for one to be read, and then another
* etc.
*/
void bread_page(unsigned long address,int dev,int b[4])
{
struct buffer_head * bh[4];
int i;
for (i=0 ; i<4 ; i++)
if (b[i]) {
if (bh[i] = getblk(dev,b[i]))
if (!bh[i]->b_uptodate)
ll_rw_block(READ,bh[i]);
} else
bh[i] = NULL;
for (i=0 ; i<4 ; i++,address += BLOCK_SIZE)
if (bh[i]) {
wait_on_buffer(bh[i]);
if (bh[i]->b_uptodate)
COPYBLK((unsigned long) bh[i]->b_data,address);
brelse(bh[i]);
}
}
/*
* Ok, breada can be used as bread, but additionally to mark other
* blocks for reading as well. End the argument list with a negative
* number.
*/
struct buffer_head * breada(int dev,int first, ...)
{
va_list args;
struct buffer_head * bh, *tmp;
va_start(args,first);
if (!(bh=getblk(dev,first)))
panic("bread: getblk returned NULL\n");
if (!bh->b_uptodate)
ll_rw_block(READ,bh);
while ((first=va_arg(args,int))>=0) {
tmp=getblk(dev,first);
if (tmp) {
if (!tmp->b_uptodate)
ll_rw_block(READA,tmp);
tmp->b_count--;
}
}
va_end(args);
wait_on_buffer(bh);
if (bh->b_uptodate)
return bh;
brelse(bh);
return (NULL);
}
void buffer_init(long buffer_end)
{
struct buffer_head * h = start_buffer;
void * b;
int i;
if (buffer_end == 1<<20)
b = (void *) (640*1024);
else
b = (void *) buffer_end;
while ( (b -= BLOCK_SIZE) >= ((void *) (h+1)) ) {
if (((unsigned long) (h+1)) > 0xA0000) {
printk("buffer-list doesn't fit in low meg - contact Linus\n");
break;
}
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_reqnext = NULL;
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;
}