emd.c

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 * call umsdos_writeentry().
 * 
 * To delete an entry, you find it, zero out the entry (memset)
 * and call umsdos_writeentry().
 * 
 * All this to say that umsdos_writeentry must be called after this
 * function since it relies on the f_pos field of info.
 *
 * Note: the caller must hold a lock on the parent directory.
 */
/* #Specification: EMD file structure
 * The EMD file uses a fairly simple layout.  It is made of records
 * (UMSDOS_REC_SIZE == 64).  When a name can't be written in a single
 * record, multiple contiguous records are allocated.
 */

static int umsdos_find (struct dentry *demd, struct umsdos_info *info)
{
	struct umsdos_dirent *entry = &info->entry;
	int recsize = info->recsize;
	struct inode *emd_dir;
	int ret = -ENOENT;
	struct {
		off_t posok;	/* Position available to store the entry */
		off_t one;	/* One empty position -> maybe <- large enough */
	} empty;
	int found = 0;
	int empty_size = 0;
	struct address_space *mapping;
	filler_t *readpage;
	struct page *page = NULL;
	int index = -1;
	int offs = PAGE_CACHE_SIZE,max_offs = PAGE_CACHE_SIZE;
	char *p = NULL;
	loff_t pos = 0;

	/* make sure there's an EMD file ... */
	ret = -ENOENT;
	emd_dir = demd->d_inode;
	if (!emd_dir)
		goto out_dput;
	mapping = emd_dir->i_mapping;
	readpage = (filler_t*)mapping->a_ops->readpage;

	empty.posok = emd_dir->i_size;
	while (1) {
		struct umsdos_dirent *rentry;
		int entry_size;

		if (offs >= max_offs) {
			if (page) {
				kunmap(page);
				page_cache_release(page);
				page = NULL;
			}
			if (pos >= emd_dir->i_size) {
				info->f_pos = empty.posok;
				break;
			}
			if (++index == (emd_dir->i_size>>PAGE_CACHE_SHIFT))
				max_offs = emd_dir->i_size & ~PAGE_CACHE_MASK;
			offs -= PAGE_CACHE_SIZE;
			page = read_cache_page(mapping,index,readpage,NULL);
			if (IS_ERR(page))
				goto sync_fail;
			wait_on_page(page);
			if (!Page_Uptodate(page))
				goto async_fail;
			p = kmap(page);
		}

		rentry = (struct umsdos_dirent *)(p+offs);

		if (rentry->name_len == 0) {
			/* We are looking for an empty section at least */
			/* as large as recsize. */
			if (entry->name_len == 0) {
				info->f_pos = pos;
				ret = 0;
				break;
			}
			offs += UMSDOS_REC_SIZE;
			pos += UMSDOS_REC_SIZE;
			if (found)
				continue;
			if (!empty_size)
				empty.one = pos-UMSDOS_REC_SIZE;
			empty_size += UMSDOS_REC_SIZE;
			if (empty_size == recsize) {
				/* Here is a large enough section. */
				empty.posok = empty.one;
				found = 1;
			}
			continue;
		}

		entry_size = umsdos_evalrecsize(rentry->name_len);
		if (entry_size > PAGE_CACHE_SIZE)
			goto async_fail;
		empty_size = 0;
		if (entry->name_len != rentry->name_len)
			goto skip_it;

		if (entry_size + offs > PAGE_CACHE_SIZE) {
			/* Sucker spans the page boundary */
			int len = (p+PAGE_CACHE_SIZE)-rentry->name;
			struct page *next_page;
			char *q;
			next_page = read_cache_page(mapping,index+1,readpage,NULL);
			if (IS_ERR(next_page)) {
				page_cache_release(page);
				page = next_page;
				goto sync_fail;
			}
			wait_on_page(next_page);
			if (!Page_Uptodate(next_page)) {
				page_cache_release(page);
				page = next_page;
				goto async_fail;
			}
			q = kmap(next_page);
			if (memcmp(entry->name, rentry->name, len) ||
			    memcmp(entry->name+len, q, entry->name_len-len)) {
				kunmap(next_page);
				page_cache_release(next_page);
				goto skip_it;
			}
			kunmap(next_page);
			page_cache_release(next_page);
		} else if (memcmp (entry->name, rentry->name, entry->name_len))
			goto skip_it;

		info->f_pos = pos;
		copy_entry(entry, rentry);
		ret = 0;
		break;
skip_it:
		offs+=entry_size;
		pos+=entry_size;
	}
	if (page) {
		kunmap(page);
		page_cache_release(page);
	}
	umsdos_manglename (info);

out_dput:
	dput(demd);
	return ret;

async_fail:
	page_cache_release(page);
	page = ERR_PTR(-EIO);
sync_fail:
	return PTR_ERR(page);
}


/*
 * Add a new entry in the EMD file.
 * Return 0 if OK or a negative error code.
 * Return -EEXIST if the entry already exists.
 *
 * Complete the information missing in info.
 * 
 * N.B. What if the EMD file doesn't exist?
 */

int umsdos_newentry (struct dentry *parent, struct umsdos_info *info)
{
	int err, ret = -EEXIST;
	struct dentry *demd = umsdos_get_emd_dentry(parent);

	ret = PTR_ERR(demd);
	if (IS_ERR(demd))
		goto out;
	err = umsdos_find (demd, info);
	if (err && err == -ENOENT) {
		ret = umsdos_writeentry (parent, info, 0);
		Printk (("umsdos_writeentry EMD ret = %d\n", ret));
	}
out:
	return ret;
}


/*
 * Create a new hidden link.
 * Return 0 if OK, an error code if not.
 */

/* #Specification: hard link / hidden name
 * When a hard link is created, the original file is renamed
 * to a hidden name. The name is "..LINKNNN" where NNN is a
 * number define from the entry offset in the EMD file.
 */
int umsdos_newhidden (struct dentry *parent, struct umsdos_info *info)
{
	int ret;
	struct dentry *demd = umsdos_get_emd_dentry(parent);
	ret = PTR_ERR(demd);
	if (IS_ERR(demd))
		goto out;

	umsdos_parse ("..LINK", 6, info);
	info->entry.name_len = 0;
	ret = umsdos_find (demd, info);
	if (ret == -ENOENT || ret == 0) {
		info->entry.name_len = sprintf (info->entry.name,
						"..LINK%ld", info->f_pos);
		ret = 0;
	}
out:
	return ret;
}


/*
 * Remove an entry from the EMD file.
 * Return 0 if OK, a negative error code otherwise.
 * 
 * Complete the information missing in info.
 */

int umsdos_delentry (struct dentry *parent, struct umsdos_info *info, int isdir)
{
	int ret;
	struct dentry *demd = umsdos_get_emd_dentry(parent);

	ret = PTR_ERR(demd);
	if (IS_ERR(demd))
		goto out;
	ret = umsdos_find (demd, info);
	if (ret)
		goto out;
	if (info->entry.name_len == 0)
		goto out;

	if ((isdir != 0) != (S_ISDIR (info->entry.mode) != 0)) {
		if (S_ISDIR (info->entry.mode)) {
			ret = -EISDIR;
		} else {
			ret = -ENOTDIR;
		}
		goto out;
	}
	ret = umsdos_writeentry (parent, info, 1);

out:
	return ret;
}


/*
 * Verify that an EMD directory is empty.
 * Return: 
 * 0 if not empty,
 * 1 if empty (except for EMD file),
 * 2 if empty or no EMD file.
 */

int umsdos_isempty (struct dentry *dentry)
{
	struct dentry *demd;
	int ret = 2;
	loff_t pos = 0;

	demd = umsdos_get_emd_dentry(dentry);
	if (IS_ERR(demd))
		goto out;
	/* If the EMD file does not exist, it is certainly empty. :-) */
	if (!demd->d_inode)
		goto out_dput;

	ret = 1;
	while (pos < demd->d_inode->i_size) {
		struct umsdos_dirent entry;

		if (umsdos_emd_dir_readentry (demd, &pos, &entry) != 0) {
			ret = 0;
			break;
		}
		if (entry.name_len != 0) {
			ret = 0;
			break;
		}
	}

out_dput:
	dput(demd);
out:
	return ret;
}

/*
 * Locate an entry in a EMD directory.
 * Return 0 if OK, error code if not, generally -ENOENT.
 *
 * expect argument:
 * 	0: anything
 * 	1: file
 * 	2: directory
 */

int umsdos_findentry (struct dentry *parent, struct umsdos_info *info,
			int expect)
{		
	int ret;
	struct dentry *demd = umsdos_get_emd_dentry(parent);

	ret = PTR_ERR(demd);
	if (IS_ERR(demd))
		goto out;
	ret = umsdos_find (demd, info);
	if (ret)
		goto out;

	switch (expect) {
	case 1:
		if (S_ISDIR (info->entry.mode))
			ret = -EISDIR;
		break;
	case 2:
		if (!S_ISDIR (info->entry.mode))
			ret = -ENOTDIR;
	}

out:
	Printk (("umsdos_findentry: returning %d\n", ret));
	return ret;
}