Linux/buffer2.c

#define __LIBRARY__
/*
 *  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 <unistd.h>
#include <stdarg.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <linux/config.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <asm/system.h>
#include <asm/io.h>
#include <asm/segment.h>

#define BUF_MAX 4096
#define DIRBUF  8192
#define MAX_ARG_PAGES 32
#define NAME_LEN 14

extern void put_super(int dev);
extern void invalidate_inodes(int dev);

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;
}

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_dev == dev && bh->b_dirt)
			ll_rw_block(WRITE,bh);
	}
	sync_inodes();
	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_dirt)
			ll_rw_block(WRITE,bh);
	}
	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;

	if (MAJOR(dev) != 2)
		return;
	if (!floppy_change(dev & 0x03))
		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_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;

	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)
			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.
 */
#define BADNESS(bh) (((bh)->b_dirt<<1)+(bh)->b_lock)
struct buffer_head * getblk(int dev,int block)
{
	struct buffer_head * tmp, * bh;

repeat:
	if (bh = get_hash_table(dev,block))
		return bh;
	tmp = free_list;
	do {
		if (tmp->b_count)
			continue;
		if (!bh || BADNESS(tmp)<BADNESS(bh)) {
			bh = tmp;
			if (!BADNESS(tmp))
				break;
		}
/* and repeat until we find something good */
	} while ((tmp = tmp->b_next_free) != free_list);
	if (!bh) {
		sleep_on(&buffer_wait);
		goto repeat;
	}
	wait_on_buffer(bh);
	if (bh->b_count)
		goto repeat;
	while (bh->b_dirt) {
		sync_dev(bh->b_dev);
		wait_on_buffer(bh);
		if (bh->b_count)
			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) \
	)

/*
 * 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,bh);
			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)) ) {
		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;
}	

//mygetdents
/*<2A><><EFBFBD>建<EFBFBD><E5BBBA><EFBFBD><EFBFBD><EFBFBD>ṹ*/
struct linux_dirent
{
	long        d_ino;
	off_t       d_off;
	unsigned short  d_reclen;
	char            d_name[NAME_LEN+1];
};
int sys_getdents(unsigned int fd, struct linux_dirent* dirp, unsigned int
	count)
{
	struct file* file;
	struct linux_dirent mydir;
	struct dir_entry* dir;
	struct m_inode* inode;
	struct buffer_head* bh;
	char* buf;
	int i, j, dsize, ldsize;
	int num = 0;
	/*dirp<72><70>СΪ0*/
	if (!count)
		return -1;
	file = current->filp[fd];//<2F><>fd<66><64><EFBFBD><EFBFBD>filp<6C><70><EFBFBD><EFBFBD>õ<EFBFBD><C3B5><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ļ<EFBFBD>file
	inode = file->f_inode;//ͨ<><CDA8>file<6C>õ<EFBFBD><C3B5><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ڵ<EFBFBD>f_inode
	bh = bread(inode->i_dev, inode->i_zone[0]);//<2F><><EFBFBD><EFBFBD>bread<61><64><EFBFBD>豸<EFBFBD><E8B1B8>ȡ<EFBFBD><C8A1><EFBFBD>ļ<EFBFBD><C4BC><EFBFBD><EFBFBD>ݶ<EFBFBD>ӦӲ<D3A6><D3B2><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>ݣ<EFBFBD>
	                                           //<2F><><EFBFBD><EFBFBD>buffer_head<61>ṹ<EFBFBD><E1B9B9>ָ<EFBFBD><D6B8>bh
	dsize = sizeof(struct dir_entry);//<2F><>ȡdir_entry<72>ṹ<EFBFBD><E1B9B9>Ĵ<EFBFBD>С
	ldsize = sizeof(struct linux_dirent);//<2F><>ȡlinux_dirent<6E>ṹ<EFBFBD><E1B9B9>Ĵ<EFBFBD>С
	for (j = 0; j < inode->i_size; j += dsize)
	{
		if (num + ldsize >= count)
			return 0;

		dir = (struct dir_entry*)(bh->b_data + j);
		if (dir->inode)
		{
			mydir.d_ino = dir->inode;
			for (i = 0; i < NAME_LEN; i++)
				mydir.d_name[i] = dir->name[i];
			mydir.d_off = 0;
			mydir.d_reclen = sizeof(mydir);
			buf = &mydir;
			for (i = 0; i < mydir.d_reclen; i++)
			{
				put_fs_byte(*(buf + i), ((char*)dirp) + i + num);
			}
			num += mydir.d_reclen;
		}
		else
			continue;
	}
	return num;
}

//mygetcwd
typedef struct
{
	int	d_fd;			
	int	d_off;			
	int	d_size;		
	char* d_buf;		
}	DIR;			

struct direct {
	ino_t d_ino;
	char d_name[NAME_LEN];
};

static struct linux_dirent res;
_syscall3(int, read, int, fildes, char*, buf, off_t, count)         
_syscall2(int, fstat, int, fildes, struct stat*, stat_buf)          
_syscall2(int, stat, const char*, filename, struct stat*, stat_buf) 
_syscall1(int, chdir, const char*, filename)                        
struct linux_dirent* readdir(DIR* dir)             
{                                           
	struct direct* ptr;                       
											  
	if (!dir) {
		errno = EBADF;
		return NULL;
	}
	if (!dir->d_buf)
		if (!(dir->d_buf = malloc(DIRBUF)))
			return NULL;
		else
			dir->d_size = dir->d_off = 0;
	while (1) {
		if (dir->d_size <= dir->d_off) {
			dir->d_off = 0;
			dir->d_size = read(dir->d_fd, dir->d_buf, DIRBUF);
		}
		if (dir->d_size <= 0)
			return NULL;
		ptr = (struct direct*)(dir->d_off + dir->d_buf);
		dir->d_off += sizeof(*ptr);
		if (!ptr->d_ino)
			continue;
		res.d_ino = ptr->d_ino;
		strncpy(res.d_name, ptr->d_name, NAME_LEN);
		res.d_name[NAME_LEN] = 0;
		res.d_reclen = strlen(res.d_name);
		return &res;
	}
}
int closedir(DIR* dir)       
{
	int fd;

	if (!dir) {
		errno = EBADF;
		return -1;
	}
	fd = dir->d_fd;
	free(dir->d_buf);
	free(dir);
	return close(fd);
}
DIR* opendir(const char* dirname)         
{
	int fd;
	struct stat stat_buf;
	DIR* ptr;

	if ((fd = open(dirname, O_RDONLY)) < 0) 
		return NULL;
	if (fstat(fd, &stat_buf) < 0 ||          
		!S_ISDIR(stat_buf.st_mode) ||
		!(ptr = malloc(sizeof(*ptr)))) {
		close(fd);
		return NULL;
	}
	memset(ptr, 0, sizeof(*ptr));
	ptr->d_fd = fd;
	return ptr;
}
char* sys_getcwd(char* buf, size_t size) {
	char path[BUF_MAX], cwd[BUF_MAX];
	DIR* dirp;
	struct linux_dirent* dp;
	struct stat state0, state1, state2;
	dev_t dev;
	ino_t ino;

	while (1) {
		if (stat(".", &state0 == 0)) {            
			dev = state0.st_dev;
			ino = state0.st_ino;
		}

		dirp = opendir("..");                          
		stat("..", &state2);                         
		if (state2.st_dev == dev && state2.st_ino == ino)
			break;                                            

		while ((dp = readdir(dirp)) != NULL) {           
			memcpy(path, dp->d_name, BUF_MAX);          
			stat(path, &state1);                             

			if (dev == state1.st_dev && ino == state1.st_ino) {
				memset(cwd, 0, sizeof(cwd));                    
				strcat(cwd, "/");
				strcat(cwd, dp->d_name);
				strcat(cwd, buf);                               
				strncpy(buf, cwd, BUF_MAX);                     
				break;
			}
		}
		closedir(dirp);
		chdir("..");											
	}
	return buf;
}