namei.c

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/*
 *  linux/fs/umsdos/namei.c
 *
 *      Written 1993 by Jacques Gelinas 
 *      Inspired from linux/fs/msdos/... by Werner Almesberger
 *
 * Maintain and access the --linux alternate directory file.
 */
 /*
  * You are in the maze of twisted functions - half of them shouldn't
  * be here...
  */

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/msdos_fs.h>
#include <linux/umsdos_fs.h>
#include <linux/slab.h>

#define UMSDOS_DIR_LOCK

#ifdef UMSDOS_DIR_LOCK

static inline void u_sleep_on (struct inode *dir)
{
	sleep_on (&dir->u.umsdos_i.dir_info.p);
}

static inline void u_wake_up (struct inode *dir)
{
    	wake_up (&dir->u.umsdos_i.dir_info.p);
}

/*
 * Wait for creation exclusivity.
 * Return 0 if the dir was already available.
 * Return 1 if a wait was necessary.
 * When 1 is return, it means a wait was done. It does not
 * mean the directory is available.
 */
static int umsdos_waitcreate (struct inode *dir)
{
	int ret = 0;

	if (dir->u.umsdos_i.dir_info.creating
	    && dir->u.umsdos_i.dir_info.pid != current->pid) {
	    	PRINTK (("creating && dir_info.pid=%lu, current->pid=%u\n", dir->u.umsdos_i.dir_info.pid, current->pid));
	    	u_sleep_on (dir);
		ret = 1;
	}
	return ret;
}

/*
 * Wait for any lookup process to finish
 */
static void umsdos_waitlookup (struct inode *dir)
{
	while (dir->u.umsdos_i.dir_info.looking) {
	    	u_sleep_on (dir);
	}
}

/*
 * Lock all other process out of this directory.
 */
/* #Specification: file creation / not atomic
 * File creation is a two step process. First we create (allocate)
 * an entry in the EMD file and then (using the entry offset) we
 * build a unique name for MSDOS. We create this name in the msdos
 * space.
 * 
 * We have to use semaphore (sleep_on/wake_up) to prevent lookup
 * into a directory when we create a file or directory and to
 * prevent creation while a lookup is going on. Since many lookup
 * may happen at the same time, the semaphore is a counter.
 * 
 * Only one creation is allowed at the same time. This protection
 * may not be necessary. The problem arise mainly when a lookup
 * or a readdir is done while a file is partially created. The
 * lookup process see that as a "normal" problem and silently
 * erase the file from the EMD file. Normal because a file
 * may be erased during a MSDOS session, but not removed from
 * the EMD file.
 * 
 * The locking is done on a directory per directory basis. Each
 * directory inode has its wait_queue.
 * 
 * For some operation like hard link, things even get worse. Many
 * creation must occur at once (atomic). To simplify the design
 * a process is allowed to recursively lock the directory for
 * creation. The pid of the locking process is kept along with
 * a counter so a second level of locking is granted or not.
 */
void umsdos_lockcreate (struct inode *dir)
{
	/*
	 * Wait for any creation process to finish except
	 * if we (the process) own the lock
	 */
	while (umsdos_waitcreate (dir) != 0);
	dir->u.umsdos_i.dir_info.creating++;
	dir->u.umsdos_i.dir_info.pid = current->pid;
	umsdos_waitlookup (dir);
}

/*
 * Lock all other process out of those two directories.
 */
static void umsdos_lockcreate2 (struct inode *dir1, struct inode *dir2)
{
	/*
	 * We must check that both directory are available before
	 * locking anyone of them. This is to avoid some deadlock.
	 * Thanks to [e-mail] (GLAUDE DAVID) for pointing
	 * this to me.
	 */
	while (1) {
		if (umsdos_waitcreate (dir1) == 0
		    && umsdos_waitcreate (dir2) == 0) {
			/* We own both now */
			dir1->u.umsdos_i.dir_info.creating++;
			dir1->u.umsdos_i.dir_info.pid = current->pid;
			dir2->u.umsdos_i.dir_info.creating++;
			dir2->u.umsdos_i.dir_info.pid = current->pid;
			break;
		}
	}
	umsdos_waitlookup (dir1);
	umsdos_waitlookup (dir2);
}

/*
 * Wait until creation is finish in this directory.
 */
void umsdos_startlookup (struct inode *dir)
{
	while (umsdos_waitcreate (dir) != 0);
	dir->u.umsdos_i.dir_info.looking++;
}

/*
 * Unlock the directory.
 */
void umsdos_unlockcreate (struct inode *dir)
{
	dir->u.umsdos_i.dir_info.creating--;
	if (dir->u.umsdos_i.dir_info.creating < 0) {
		printk ("UMSDOS: dir->u.umsdos_i.dir_info.creating < 0: %d"
			,dir->u.umsdos_i.dir_info.creating);
	}
    	u_wake_up (dir);
}

/*
 * Tell directory lookup is over.
 */
void umsdos_endlookup (struct inode *dir)
{
	dir->u.umsdos_i.dir_info.looking--;
	if (dir->u.umsdos_i.dir_info.looking < 0) {
		printk ("UMSDOS: dir->u.umsdos_i.dir_info.looking < 0: %d"
			,dir->u.umsdos_i.dir_info.looking);
	}
    	u_wake_up (dir);
}

#else
static void umsdos_lockcreate (struct inode *dir)
{
}
static void umsdos_lockcreate2 (struct inode *dir1, struct inode *dir2)
{
}
void umsdos_startlookup (struct inode *dir)
{
}
static void umsdos_unlockcreate (struct inode *dir)
{
}
void umsdos_endlookup (struct inode *dir)
{
}

#endif

static int umsdos_nevercreat (struct inode *dir, struct dentry *dentry,
				int errcod)
{
	int ret = 0;

	if (umsdos_is_pseudodos (dir, dentry)) {
		/* #Specification: pseudo root / any file creation /DOS
		 * The pseudo sub-directory /DOS can't be created!
		 * EEXIST is returned.
		 * 
		 * The pseudo sub-directory /DOS can't be removed!
		 * EPERM is returned.
		 */
		ret = errcod;
	}
	return ret;
}

/*
 * Add a new file (ordinary or special) into the alternate directory.
 * The file is added to the real MSDOS directory. If successful, it
 * is then added to the EMD file.
 * 
 * Return the status of the operation. 0 mean success.
 *
 * #Specification: create / file exists in DOS
 * Here is a situation: we are trying to create a file with
 * UMSDOS. The file is unknown to UMSDOS but already
 * exists in the DOS directory.
 * 
 * Here is what we are NOT doing:
 * 
 * We could silently assume that everything is fine
 * and allows the creation to succeed.
 * 
 * It is possible not all files in the partition
 * are meant to be visible from linux. By trying to create
 * those file in some directory, one user may get access
 * to those file without proper permissions. Looks like
 * a security hole to me. Off course sharing a file system
 * with DOS is some kind of security hole :-)
 * 
 * So ?
 * 
 * We return EEXIST in this case.
 * The same is true for directory creation.
 */
static int umsdos_create_any (struct inode *dir, struct dentry *dentry,
				int mode, int rdev, char flags)
{
	struct dentry *fake;
	struct inode *inode;
	int ret;
	struct umsdos_info info;

	ret = umsdos_nevercreat (dir, dentry, -EEXIST);
	if (ret)
		goto out;

	ret = umsdos_parse (dentry->d_name.name, dentry->d_name.len, &info);
	if (ret)
		goto out;

	info.entry.mode = mode;
	info.entry.rdev = rdev;
	info.entry.flags = flags;
	info.entry.uid = current->fsuid;
	info.entry.gid = (dir->i_mode & S_ISGID) ? dir->i_gid : current->fsgid;
	info.entry.ctime = info.entry.atime = info.entry.mtime = CURRENT_TIME;
	info.entry.nlink = 1;
	ret = umsdos_newentry (dentry->d_parent, &info);
	if (ret)
		goto out;

	/* do a real lookup to get the short name dentry */
	fake = umsdos_covered(dentry->d_parent, info.fake.fname, info.fake.len);
	ret = PTR_ERR(fake);
	if (IS_ERR(fake))
		goto out_remove;

	/* should not exist yet ... */
	ret = -EEXIST;
	if (fake->d_inode)
		goto out_remove_dput;

	ret = msdos_create (dir, fake, S_IFREG | 0777);
	if (ret)
		goto out_remove_dput;

	inode = fake->d_inode;
	atomic_inc(&inode->i_count);
	d_instantiate (dentry, inode);
	dput(fake);
	if (atomic_read(&inode->i_count) > 1) {
		printk(KERN_WARNING
			"umsdos_create_any: %s/%s, ino=%ld, icount=%d??\n",
			dentry->d_parent->d_name.name, dentry->d_name.name,
			inode->i_ino, atomic_read(&inode->i_count));
	}
	umsdos_lookup_patch_new(dentry, &info);

out:
	return ret;

	/* Creation failed ... remove the EMD entry */
out_remove_dput:
	dput(fake);
out_remove:
	if (ret == -EEXIST)
		printk(KERN_WARNING "UMSDOS: out of sync, deleting %s/%s\n",
			dentry->d_parent->d_name.name, info.fake.fname);
	umsdos_delentry (dentry->d_parent, &info, S_ISDIR (info.entry.mode));
	goto out;
}

/*
 * Add a new file into the alternate directory.
 * The file is added to the real MSDOS directory. If successful, it
 * is then added to the EMD file.
 * 
 * Return the status of the operation. 0 mean success.
 */
int UMSDOS_create (struct inode *dir, struct dentry *dentry, int mode)
{
	return umsdos_create_any (dir, dentry, mode, 0, 0);
}


/*
 * Initialise the new_entry from the old for a rename operation.
 * (Only useful for umsdos_rename_f() below).
 */
static void umsdos_ren_init (struct umsdos_info *new_info,
			     struct umsdos_info *old_info)
{
	new_info->entry.mode = old_info->entry.mode;
	new_info->entry.rdev = old_info->entry.rdev;
	new_info->entry.uid = old_info->entry.uid;
	new_info->entry.gid = old_info->entry.gid;
	new_info->entry.ctime = old_info->entry.ctime;
	new_info->entry.atime = old_info->entry.atime;
	new_info->entry.mtime = old_info->entry.mtime;
	new_info->entry.flags = old_info->entry.flags;
	new_info->entry.nlink = old_info->entry.nlink;
}

/*
 * Rename a file (move) in the file system.
 */
 
static int umsdos_rename_f (struct inode *old_dir, struct dentry *old_dentry,
			    struct inode *new_dir, struct dentry *new_dentry,
			    int flags)
{
	struct inode *old_inode = old_dentry->d_inode;
	struct dentry *old, *new, *old_emd;
	int err, ret;
	struct umsdos_info old_info;
	struct umsdos_info new_info;

 	ret = -EPERM;
	err = umsdos_parse (old_dentry->d_name.name,
				old_dentry->d_name.len, &old_info);
	if (err)
		goto out;
	err = umsdos_parse (new_dentry->d_name.name,
				new_dentry->d_name.len, &new_info);
	if (err)
		goto out;

	/* Get the EMD dentry for the old parent */
	old_emd = umsdos_get_emd_dentry(old_dentry->d_parent);
	ret = PTR_ERR(old_emd);
	if (IS_ERR(old_emd))
		goto out;

	umsdos_lockcreate2 (old_dir, new_dir);

	ret = umsdos_findentry(old_emd->d_parent, &old_info, 0);
	if (ret)
		goto out_unlock;

	err = umsdos_findentry(new_dentry->d_parent, &new_info, 0);
	if (err == 0) {
		/* check whether it _really_ exists ... */
		ret = -EEXIST;
		if (new_dentry->d_inode)
			goto out_unlock;

		/* bogus lookup? complain and fix up the EMD ... */
		printk(KERN_WARNING
			"umsdos_rename_f: entry %s/%s exists, inode NULL??\n",
			new_dentry->d_parent->d_name.name, new_info.entry.name);
		err = umsdos_delentry(new_dentry->d_parent, &new_info,
					S_ISDIR(new_info.entry.mode));
	}

	umsdos_ren_init (&new_info, &old_info);
	if (flags)
		new_info.entry.flags = flags;
	ret = umsdos_newentry (new_dentry->d_parent, &new_info);
	if (ret)
		goto out_unlock;

	/* If we're moving a hardlink, drop it first */
	if (old_info.entry.flags & UMSDOS_HLINK) {
		d_drop(old_dentry);
	}

	old = umsdos_covered(old_dentry->d_parent, old_info.fake.fname, 
					old_info.fake.len);
	ret = PTR_ERR(old);
	if (IS_ERR(old))
		goto out_unlock;
	/* make sure it's the same inode! */
	ret = -ENOENT;
	/*
	 * note: for hardlinks they will be different!
	 *  old_inode will contain inode of .LINKxxx file containing data, and
	 *  old->d_inode will contain inode of file containing path to .LINKxxx file
	 */
	if (!(old_info.entry.flags & UMSDOS_HLINK)) {
	 	if (old->d_inode != old_inode)
 			goto out_dput;
	}

	new = umsdos_covered(new_dentry->d_parent, new_info.fake.fname, 
					new_info.fake.len);
	ret = PTR_ERR(new);
	if (IS_ERR(new))
		goto out_dput;

	/* Do the msdos-level rename */
	ret = msdos_rename (old_dir, old, new_dir, new);

	dput(new);

	/* If the rename failed, remove the new EMD entry */
	if (ret != 0) {
		umsdos_delentry (new_dentry->d_parent, &new_info,
				 S_ISDIR (new_info.entry.mode));
		goto out_dput;
	}

	/*
	 * Rename successful ... remove the old name from the EMD.
	 * Note that we use the EMD parent here, as the old dentry
	 * may have moved to a new parent ...
	 */
	err = umsdos_delentry (old_emd->d_parent, &old_info,
				S_ISDIR (old_info.entry.mode));
	if (err) {
		/* Failed? Complain a bit, but don't fail the operation */
		printk(KERN_WARNING 
			"umsdos_rename_f: delentry %s/%s failed, error=%d\n",
			old_emd->d_parent->d_name.name, old_info.entry.name,
			err);
	}

	/*
	 * Update f_pos so notify_change will succeed
	 * if the file was already in use.
	 */
	umsdos_set_dirinfo_new(old_dentry, new_info.f_pos);

	/* dput() the dentry if we haven't already */
out_dput:
	dput(old);

out_unlock:
	dput(old_emd);
	umsdos_unlockcreate (old_dir);
	umsdos_unlockcreate (new_dir);

out:
	Printk ((" _ret=%d\n", ret));
	return ret;
}

/*
 * Setup a Symbolic link or a (pseudo) hard link
 * Return a negative error code or 0 if OK.
 */
/* #Specification: symbolic links / strategy
 * A symbolic link is simply a file which holds a path. It is
 * implemented as a normal MSDOS file (not very space efficient :-()
 * 
 * I see two different ways to do this: One is to place the link data
 * in unused entries of the EMD file; the other is to have a separate
 * file dedicated to hold all symbolic links data.
 * 
 * Let's go for simplicity...
 */

/*
 * AV. Should be called with dir->i_sem down.
 */
static int umsdos_symlink_x (struct inode *dir, struct dentry *dentry,
			const char *symname, int mode, char flags)
{
	int ret, len;

	ret = umsdos_create_any (dir, dentry, mode, 0, flags);
	if (ret) {
		printk(KERN_WARNING
			"umsdos_symlink: create failed, ret=%d\n", ret);
		goto out;
	}

	len = strlen (symname) + 1;
	ret = block_symlink(dentry->d_inode, symname, len);
	if (ret < 0)
		goto out_unlink;
out:
	return ret;

out_unlink:
	printk(KERN_WARNING "umsdos_symlink: write failed, unlinking\n");
	UMSDOS_unlink (dir, dentry);
	d_drop(dentry);
	goto out;
}

/*
 * Setup a Symbolic link.
 * Return a negative error code or 0 if OK.
 */
int UMSDOS_symlink ( struct inode *dir, struct dentry *dentry,
		 const char *symname)
{
	return umsdos_symlink_x (dir, dentry, symname, S_IFLNK | 0777, 0);
}

/*
 * Add a link to an inode in a directory
 */
int UMSDOS_link (struct dentry *olddentry, struct inode *dir,
		 struct dentry *dentry)
{
	struct inode *oldinode = olddentry->d_inode;
	struct inode *olddir = olddentry->d_parent->d_inode;
	struct dentry *temp;
	char *path;
	unsigned long buffer;
	int ret;
	struct umsdos_info old_info;
	struct umsdos_info hid_info;

#ifdef UMSDOS_DEBUG_VERBOSE
printk("umsdos_link: new %s/%s -> %s/%s\n",
dentry->d_parent->d_name.name, dentry->d_name.name, 
olddentry->d_parent->d_name.name, olddentry->d_name.name);
#endif
 
	ret = -EPERM;
	if (S_ISDIR (oldinode->i_mode))
		goto out;

	ret = umsdos_nevercreat (dir, dentry, -EPERM);
	if (ret)
		goto out;

	ret = -ENOMEM;
	buffer = get_free_page(GFP_KERNEL);
	if (!buffer)
		goto out;

	/*
	 * Lock the link parent if it's not the same directory.
	 */
	ret = -EDEADLOCK;
	if (olddir != dir) {