inode.c

linux 内核源代码

/*
 * ROMFS file system, Linux implementation
 *
 * Copyright (C) 1997-1999  Janos Farkas <[e-mail]>
 *
 * Using parts of the minix filesystem
 * Copyright (C) 1991, 1992  Linus Torvalds
 *
 * and parts of the affs filesystem additionally
 * Copyright (C) 1993  Ray Burr
 * Copyright (C) 1996  Hans-Joachim Widmaier
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 * Changes
 *					Changed for 2.1.19 modules
 *	Jan 1997			Initial release
 *	Jun 1997			2.1.43+ changes
 *					Proper page locking in readpage
 *					Changed to work with 2.1.45+ fs
 *	Jul 1997			Fixed follow_link
 *			2.1.47
 *					lookup shouldn't return -ENOENT
 *					from Horst von Brand:
 *					  fail on wrong checksum
 *					  double unlock_super was possible
 *					  correct namelen for statfs
 *					spotted by Bill Hawes:
 *					  readlink shouldn't iput()
 *	Jun 1998	2.1.106		from Avery Pennarun: glibc scandir()
 *					  exposed a problem in readdir
 *			2.1.107		code-freeze spellchecker run
 *	Aug 1998			2.1.118+ VFS changes
 *	Sep 1998	2.1.122		another VFS change (follow_link)
 *	Apr 1999	2.2.7		no more EBADF checking in
 *					  lookup/readdir, use ERR_PTR
 *	Jun 1999	2.3.6		d_alloc_root use changed
 *			2.3.9		clean up usage of ENOENT/negative
 *					  dentries in lookup
 *					clean up page flags setting
 *					  (error, uptodate, locking) in
 *					  in readpage
 *					use init_special_inode for
 *					  fifos/sockets (and streamline) in
 *					  read_inode, fix _ops table order
 *	Aug 1999	2.3.16		__initfunc() => __init change
 *	Oct 1999	2.3.24		page->owner hack obsoleted
 *	Nov 1999	2.3.27		2.3.25+ page->offset => index change
 */

/* todo:
 *	- see Documentation/filesystems/romfs.txt
 *	- use allocated, not stack memory for file names?
 *	- considering write access...
 *	- network (tftp) files?
 *	- merge back some _op tables
 */

/*
 * Sorry about some optimizations and for some goto's.  I just wanted
 * to squeeze some more bytes out of this code.. :)
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/romfs_fs.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/smp_lock.h>
#include <linux/buffer_head.h>
#include <linux/vfs.h>

#include <asm/uaccess.h>

struct romfs_inode_info {
	unsigned long i_metasize;	/* size of non-data area */
	unsigned long i_dataoffset;	/* from the start of fs */
	struct inode vfs_inode;
};

/* instead of private superblock data */
static inline unsigned long romfs_maxsize(struct super_block *sb)
{
	return (unsigned long)sb->s_fs_info;
}

static inline struct romfs_inode_info *ROMFS_I(struct inode *inode)
{
	return container_of(inode, struct romfs_inode_info, vfs_inode);
}

static __u32
romfs_checksum(void *data, int size)
{
	__u32 sum;
	__be32 *ptr;

	sum = 0; ptr = data;
	size>>=2;
	while (size>0) {
		sum += be32_to_cpu(*ptr++);
		size--;
	}
	return sum;
}

static const struct super_operations romfs_ops;

static int romfs_fill_super(struct super_block *s, void *data, int silent)
{
	struct buffer_head *bh;
	struct romfs_super_block *rsb;
	struct inode *root;
	int sz;

	/* I would parse the options here, but there are none.. :) */

	sb_set_blocksize(s, ROMBSIZE);
	s->s_maxbytes = 0xFFFFFFFF;

	bh = sb_bread(s, 0);
	if (!bh) {
		/* XXX merge with other printk? */
                printk ("romfs: unable to read superblock\n");
		goto outnobh;
	}

	rsb = (struct romfs_super_block *)bh->b_data;
	sz = be32_to_cpu(rsb->size);
	if (rsb->word0 != ROMSB_WORD0 || rsb->word1 != ROMSB_WORD1
	   || sz < ROMFH_SIZE) {
		if (!silent)
			printk ("VFS: Can't find a romfs filesystem on dev "
				"%s.\n", s->s_id);
		goto out;
	}
	if (romfs_checksum(rsb, min_t(int, sz, 512))) {
		printk ("romfs: bad initial checksum on dev "
			"%s.\n", s->s_id);
		goto out;
	}

	s->s_magic = ROMFS_MAGIC;
	s->s_fs_info = (void *)(long)sz;

	s->s_flags |= MS_RDONLY;

	/* Find the start of the fs */
	sz = (ROMFH_SIZE +
	      strnlen(rsb->name, ROMFS_MAXFN) + 1 + ROMFH_PAD)
	     & ROMFH_MASK;

	s->s_op	= &romfs_ops;
	root = iget(s, sz);
	if (!root)
		goto out;

	s->s_root = d_alloc_root(root);
	if (!s->s_root)
		goto outiput;

	brelse(bh);
	return 0;

outiput:
	iput(root);
out:
	brelse(bh);
outnobh:
	return -EINVAL;
}

/* That's simple too. */

static int
romfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
	buf->f_type = ROMFS_MAGIC;
	buf->f_bsize = ROMBSIZE;
	buf->f_bfree = buf->f_bavail = buf->f_ffree;
	buf->f_blocks = (romfs_maxsize(dentry->d_sb)+ROMBSIZE-1)>>ROMBSBITS;
	buf->f_namelen = ROMFS_MAXFN;
	return 0;
}

/* some helper routines */

static int
romfs_strnlen(struct inode *i, unsigned long offset, unsigned long count)
{
	struct buffer_head *bh;
	unsigned long avail, maxsize, res;

	maxsize = romfs_maxsize(i->i_sb);
	if (offset >= maxsize)
		return -1;

	/* strnlen is almost always valid */
	if (count > maxsize || offset+count > maxsize)
		count = maxsize-offset;

	bh = sb_bread(i->i_sb, offset>>ROMBSBITS);
	if (!bh)
		return -1;		/* error */

	avail = ROMBSIZE - (offset & ROMBMASK);
	maxsize = min_t(unsigned long, count, avail);
	res = strnlen(((char *)bh->b_data)+(offset&ROMBMASK), maxsize);
	brelse(bh);

	if (res < maxsize)
		return res;		/* found all of it */

	while (res < count) {
		offset += maxsize;

		bh = sb_bread(i->i_sb, offset>>ROMBSBITS);
		if (!bh)
			return -1;
		maxsize = min_t(unsigned long, count - res, ROMBSIZE);
		avail = strnlen(bh->b_data, maxsize);
		res += avail;
		brelse(bh);
		if (avail < maxsize)
			return res;
	}
	return res;
}

static int
romfs_copyfrom(struct inode *i, void *dest, unsigned long offset, unsigned long count)
{
	struct buffer_head *bh;
	unsigned long avail, maxsize, res;

	maxsize = romfs_maxsize(i->i_sb);
	if (offset >= maxsize || count > maxsize || offset+count>maxsize)
		return -1;

	bh = sb_bread(i->i_sb, offset>>ROMBSBITS);
	if (!bh)
		return -1;		/* error */

	avail = ROMBSIZE - (offset & ROMBMASK);
	maxsize = min_t(unsigned long, count, avail);
	memcpy(dest, ((char *)bh->b_data) + (offset & ROMBMASK), maxsize);
	brelse(bh);

	res = maxsize;			/* all of it */

	while (res < count) {
		offset += maxsize;
		dest += maxsize;

		bh = sb_bread(i->i_sb, offset>>ROMBSBITS);
		if (!bh)
			return -1;
		maxsize = min_t(unsigned long, count - res, ROMBSIZE);
		memcpy(dest, bh->b_data, maxsize);
		brelse(bh);
		res += maxsize;
	}
	return res;
}

static unsigned char romfs_dtype_table[] = {
	DT_UNKNOWN, DT_DIR, DT_REG, DT_LNK, DT_BLK, DT_CHR, DT_SOCK, DT_FIFO
};

static int
romfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
{
	struct inode *i = filp->f_path.dentry->d_inode;
	struct romfs_inode ri;
	unsigned long offset, maxoff;
	int j, ino, nextfh;
	int stored = 0;
	char fsname[ROMFS_MAXFN];	/* XXX dynamic? */

	lock_kernel();

	maxoff = romfs_maxsize(i->i_sb);

	offset = filp->f_pos;
	if (!offset) {
		offset = i->i_ino & ROMFH_MASK;
		if (romfs_copyfrom(i, &ri, offset, ROMFH_SIZE) <= 0)
			goto out;
		offset = be32_to_cpu(ri.spec) & ROMFH_MASK;
	}

	/* Not really failsafe, but we are read-only... */
	for(;;) {
		if (!offset || offset >= maxoff) {
			offset = maxoff;
			filp->f_pos = offset;
			goto out;
		}
		filp->f_pos = offset;

		/* Fetch inode info */
		if (romfs_copyfrom(i, &ri, offset, ROMFH_SIZE) <= 0)
			goto out;

		j = romfs_strnlen(i, offset+ROMFH_SIZE, sizeof(fsname)-1);
		if (j < 0)
			goto out;

		fsname[j]=0;
		romfs_copyfrom(i, fsname, offset+ROMFH_SIZE, j);

		ino = offset;
		nextfh = be32_to_cpu(ri.next);
		if ((nextfh & ROMFH_TYPE) == ROMFH_HRD)
			ino = be32_to_cpu(ri.spec);
		if (filldir(dirent, fsname, j, offset, ino,
			    romfs_dtype_table[nextfh & ROMFH_TYPE]) < 0) {
			goto out;