file.c

Linux内核源代码 为压缩文件 是<<Linux内核>>一书中的源代码

/*
 *  linux/fs/affs/file.c
 *
 *  (c) 1996  Hans-Joachim Widmaier - Rewritten
 *
 *  (C) 1993  Ray Burr - Modified for Amiga FFS filesystem.
 *
 *  (C) 1992  Eric Youngdale Modified for ISO 9660 filesystem.
 *
 *  (C) 1991  Linus Torvalds - minix filesystem
 *
 *  affs regular file handling primitives
 */

#define DEBUG 0
#include <asm/div64.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#include <linux/sched.h>
#include <linux/affs_fs.h>
#include <linux/fcntl.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/malloc.h>
#include <linux/stat.h>
#include <linux/locks.h>
#include <linux/smp_lock.h>
#include <linux/dirent.h>
#include <linux/fs.h>
#include <linux/amigaffs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>

#define MIN(a,b) (((a)<(b))?(a):(b))
#define MAX(a,b) (((a)>(b))?(a):(b))

#if PAGE_SIZE < 4096
#error PAGE_SIZE must be at least 4096
#endif

static struct buffer_head *affs_getblock(struct inode *inode, s32 block);
static ssize_t affs_file_read_ofs(struct file *filp, char *buf, size_t count, loff_t *ppos);
static ssize_t affs_file_write(struct file *filp, const char *buf, size_t count, loff_t *ppos);
static ssize_t affs_file_write_ofs(struct file *filp, const char *buf, size_t cnt, loff_t *ppos);
static int alloc_ext_cache(struct inode *inode);

struct file_operations affs_file_operations = {
	read:		generic_file_read,
	write:		affs_file_write,
	mmap:		generic_file_mmap,
	fsync:		file_fsync,
};

struct inode_operations affs_file_inode_operations = {
	truncate:	affs_truncate,
	setattr:	affs_notify_change,
};

struct file_operations affs_file_operations_ofs = {
	read:		affs_file_read_ofs,
	write:		affs_file_write_ofs,
	fsync:		file_fsync,
};

#define AFFS_ISINDEX(x)	((x < 129) ||				\
			 (x < 512 && (x & 1) == 0) ||		\
			 (x < 1024 && (x & 3) == 0) ||		\
			 (x < 2048 && (x & 15) == 0) ||		\
			 (x < 4096 && (x & 63) == 0) ||		\
			 (x < 20480 && (x & 255) == 0) ||	\
			 (x < 36864 && (x & 511) == 0))

/* The keys of the extension blocks are stored in a 512-entry
 * deep cache. In order to save memory, not every key of later
 * extension blocks is stored - the larger the file gets, the
 * bigger the holes in between.
 */

static int
seqnum_to_index(int seqnum)
{
	/* All of the first 127 keys are stored */
	if (seqnum < 128)
		return seqnum;
	seqnum -= 128;

	/* Of the next 384 keys, every 2nd is kept */
	if (seqnum < (192 * 2))
		return 128 + (seqnum >> 1);
	seqnum -= 192 * 2;
	
	/* Every 4th of the next 512 */
	if (seqnum < (128 * 4))
		return 128 + 192 + (seqnum >> 2);
	seqnum -= 128 * 4;

	/* Every 16th of the next 1024 */
	if (seqnum < (64 * 16))
		return 128 + 192 + 128 + (seqnum >> 4);
	seqnum -= 64 * 16;

	/* Every 64th of the next 2048 */
	if (seqnum < (32 * 64))
		return 128 + 192 + 128 + 64 + (seqnum >> 6);
	seqnum -= 32 * 64;

	/* Every 256th of the next 16384 */
	if (seqnum < (64 * 256))
		return 128 + 192 + 128 + 64 + 32 + (seqnum >> 8);
	seqnum -= 64 * 256;

	/* Every 512th upto 36479 (1.3 GB with 512 byte blocks).
	 * Seeking to positions behind this will get slower
	 * than dead snails nailed to the ground. But if
	 * someone uses files that large with 512-byte blocks,
	 * he or she deserves no better.
	 */
	
	if (seqnum > (31 * 512))
		seqnum = 31 * 512;
	return 128 + 192 + 128 + 64 + 32 + 64 + (seqnum >> 9);
}

/* Now the other way round: Calculate the sequence
 * number of an extension block of a key at the
 * given index in the cache.
 */

static int
index_to_seqnum(int index)
{
	if (index < 128)
		return index;
	index -= 128;
	if (index < 192)
		return 128 + (index << 1);
	index -= 192;
	if (index < 128)
		return 128 + 192 * 2 + (index << 2);
	index -= 128;
	if (index < 64)
		return 128 + 192 * 2 + 128 * 4 + (index << 4);
	index -= 64;
	if (index < 32)
		return 128 + 192 * 2 + 128 * 4 + 64 * 16 + (index << 6);
	index -= 32;
	if (index < 64)
		return 128 + 192 * 2 + 128 * 4 + 64 * 16 + 32 * 64 + (index << 8);
	index -= 64;
	return 128 + 192 * 2 + 128 * 4 + 64 * 16 + 32 * 64 + 64 * 256 + (index << 9);
}

static s32 __inline__
calc_key(struct inode *inode, int *ext)
{
	int		  index;
	struct key_cache *kc;

	for (index = 0; index < 4; index++) {
		kc = &inode->u.affs_i.i_ec->kc[index];
		if (kc->kc_last == -1)
			continue;	/* don't look in cache if invalid. */
		if (*ext == kc->kc_this_seq) {
			return kc->kc_this_key;
		} else if (*ext == kc->kc_this_seq + 1) {
			if (kc->kc_next_key)
				return kc->kc_next_key;
			else {
				(*ext)--;
				return kc->kc_this_key;
			}
		}
	}
	index = seqnum_to_index(*ext);
	if (index > inode->u.affs_i.i_ec->max_ext)
		index = inode->u.affs_i.i_ec->max_ext;
	*ext = index_to_seqnum(index);
	return inode->u.affs_i.i_ec->ec[index];
}

int
affs_bmap(struct inode *inode, int block)
{
	struct buffer_head	*bh;
	s32			 key, nkey;
	s32			 ptype, stype;
	int			 ext;
	int			 index;
	int			 keycount;
	struct key_cache	*kc;
	struct key_cache	*tkc;
	struct timeval		 tv;
	s32			*keyp;
	int			 i;

	pr_debug("AFFS: bmap(%lu,%d)\n",inode->i_ino,block);

	lock_kernel();
	if (block < 0) {
		affs_error(inode->i_sb,"bmap","Block < 0");
		goto out_fail;
	}
	if (!inode->u.affs_i.i_ec) {
		if (alloc_ext_cache(inode)) {
			goto out_fail;
		}
	}

	/* Try to find the requested key in the cache.
	 * In order to speed this up as much as possible,
	 * the cache line lookup is done in a separate
	 * step.
	 */

	for (i = 0; i < 4; i++) {
		tkc = &inode->u.affs_i.i_ec->kc[i];
		/* Look in any cache if the key is there */
		if (block <= tkc->kc_last && block >= tkc->kc_first) {
			unlock_kernel();
			return tkc->kc_keys[block - tkc->kc_first];
		}
	}
	kc = NULL;
	tv = xtime;
	for (i = 0; i < 4; i++) {
		tkc = &inode->u.affs_i.i_ec->kc[i];
		if (tkc->kc_lru_time.tv_sec > tv.tv_sec)
			continue;
		if (tkc->kc_lru_time.tv_sec < tv.tv_sec ||
		    tkc->kc_lru_time.tv_usec < tv.tv_usec) {
			kc = tkc;
			tv = tkc->kc_lru_time;
		}
	}
	if (!kc)	/* Really shouldn't happen */
		kc = tkc;
	kc->kc_lru_time = xtime;
	keyp            = kc->kc_keys;
	kc->kc_first    = block;
	kc->kc_last     = -1;
	keycount        = AFFS_KCSIZE;

	/* Calculate sequence number of the extension block where the
	 * number of the requested block is stored. 0 means it's in
	 * the file header.
	 */

	ext    = block / AFFS_I2HSIZE(inode);
	key    = calc_key(inode,&ext);
	block -= ext * AFFS_I2HSIZE(inode);

	for (;;) {
		bh = affs_bread(inode->i_dev,key,AFFS_I2BSIZE(inode));
		if (!bh)
			goto out_fail;

		index = seqnum_to_index(ext);
		if (index > inode->u.affs_i.i_ec->max_ext &&
		    (affs_checksum_block(AFFS_I2BSIZE(inode),bh->b_data,&ptype,&stype) ||
		     (ptype != T_SHORT && ptype != T_LIST) || stype != ST_FILE)) {
			affs_brelse(bh);
			goto out_fail;
		}
		nkey = be32_to_cpu(FILE_END(bh->b_data,inode)->extension);
		if (block < AFFS_I2HSIZE(inode)) {
			/* Fill cache as much as possible */
			if (keycount) {
				kc->kc_first = ext * AFFS_I2HSIZE(inode) + block;
				keycount     = keycount < AFFS_I2HSIZE(inode) - block ? keycount :
						AFFS_I2HSIZE(inode) - block;
				for (i = 0; i < keycount; i++)
					kc->kc_keys[i] = be32_to_cpu(AFFS_BLOCK(bh->b_data,inode,block + i));
				kc->kc_last = kc->kc_first + i - 1;
			}
			break;
		}
		block -= AFFS_I2HSIZE(inode);
		affs_brelse(bh);
		ext++;
		if (index > inode->u.affs_i.i_ec->max_ext && AFFS_ISINDEX(ext)) {
			inode->u.affs_i.i_ec->ec[index] = nkey;
			inode->u.affs_i.i_ec->max_ext   = index;
		}
		key = nkey;
	}
	kc->kc_this_key = key;
	kc->kc_this_seq = ext;
	kc->kc_next_key = nkey;
	key = be32_to_cpu(AFFS_BLOCK(bh->b_data,inode,block));
	affs_brelse(bh);
out:
	unlock_kernel();
	return key;

out_fail:
	key=0;
	goto out;
}


static int affs_get_block(struct inode *inode, long block, struct buffer_head *bh_result, int create)
{
	int err, phys=0, new=0;

	if (!create) {
		phys = affs_bmap(inode, block);
		if (phys) {
			bh_result->b_dev = inode->i_dev;
			bh_result->b_blocknr = phys;
			bh_result->b_state |= (1UL << BH_Mapped);
		}
		return 0;
	}

	err = -EIO;
	lock_kernel();
	if (block < 0)
		goto abort_negative;

	if (affs_getblock(inode, block)==NULL) {
		err = -EIO;
		goto abort;
	}

	bh_result->b_dev = inode->i_dev;
	bh_result->b_blocknr = phys;
	bh_result->b_state |= (1UL << BH_Mapped);
	if (new)
		bh_result->b_state |= (1UL << BH_New);
	
abort:
	unlock_kernel();
	return err;

abort_negative:
	affs_error(inode->i_sb,"affs_get_block","Block < 0");
	goto abort;

}
		
static int affs_writepage(struct page *page)
{
	return block_write_full_page(page,affs_get_block);
}
static int affs_readpage(struct file *file, struct page *page)
{
	return block_read_full_page(page,affs_get_block);
}
static int affs_prepare_write(struct file *file, struct page *page, unsigned from, unsigned to)
{
	return cont_prepare_write(page,from,to,affs_get_block,
		&page->mapping->host->u.affs_i.mmu_private);
}
static int _affs_bmap(struct address_space *mapping, long block)
{
	return generic_block_bmap(mapping,block,affs_get_block);
}
struct address_space_operations affs_aops = {
	readpage: affs_readpage,
	writepage: affs_writepage,
	sync_page: block_sync_page,
	prepare_write: affs_prepare_write,
	commit_write: generic_commit_write,
	bmap: _affs_bmap
};

/* With the affs, getting a random block from a file is not
 * a simple business. Since this fs does not allow holes,
 * it may be necessary to allocate all the missing blocks
 * in between, as well as some new extension blocks. The OFS
 * is even worse: All data blocks contain pointers to the
 * next ones, so you have to fix [n-1] after allocating [n].
 * What a mess.
 */

static struct buffer_head * affs_getblock(struct inode *inode, s32 block)
{
	struct super_block	*sb = inode->i_sb;
	int			 ofs = sb->u.affs_sb.s_flags & SF_OFS;
	int			 ext = block / AFFS_I2HSIZE(inode);
	struct buffer_head	*bh, *ebh, *pbh = NULL;
	struct key_cache	*kc;
	s32			 key, nkey;
	int			 cf, j, pt;
	int			 index;
	int			 err;

	pr_debug("AFFS: getblock(%lu,%d)\n",inode->i_ino,block);

	key    = calc_key(inode,&ext);
	block -= ext * AFFS_I2HSIZE(inode);
	pt     = ext ? T_LIST : T_SHORT;

	/* Key refers now to the last known extension block,
	 * ext is its sequence number (if 0, key refers to the
	 * header block), and block is the block number relative
	 * to the first block stored in that extension block.
	 */
	for (;;) {	/* Loop over header block and extension blocks */
		struct file_front *fdp;

		bh = affs_bread(inode->i_dev,key,AFFS_I2BSIZE(inode));
		if (!bh)
			goto out_fail;
		fdp = (struct file_front *) bh->b_data;
		err = affs_checksum_block(AFFS_I2BSIZE(inode),bh->b_data,&cf,&j);
		if (err || cf != pt || j != ST_FILE) {
		    	affs_error(sb, "getblock",
				"Block %d is not a valid %s", key,
				pt == T_SHORT ? "file header" : "ext block");
			goto out_free_bh;
		}
		j  = be32_to_cpu(((struct file_front *)bh->b_data)->block_count);
		for (cf = 0; j < AFFS_I2HSIZE(inode) && j <= block; j++) {
			if (ofs && !pbh && inode->u.affs_i.i_lastblock >= 0) {
				if (j > 0) {
					s32 k = AFFS_BLOCK(bh->b_data, inode, j - 1);