root.c

linux 内核源代码

		ino = list_entry(p, struct autofs_info, rehash);
		dentry = ino->dentry;

		spin_lock(&dentry->d_lock);

		/* Bad luck, we've already been dentry_iput */
		if (!dentry->d_inode)
			goto next;

		qstr = &dentry->d_name;

		if (dentry->d_name.hash != hash)
			goto next;
		if (dentry->d_parent != parent)
			goto next;

		if (qstr->len != len)
			goto next;
		if (memcmp(qstr->name, str, len))
			goto next;

		if (d_unhashed(dentry)) {
			struct autofs_info *ino = autofs4_dentry_ino(dentry);
			struct inode *inode = dentry->d_inode;

			list_del_init(&ino->rehash);
			dget(dentry);
			/*
			 * Make the rehashed dentry negative so the VFS
			 * behaves as it should.
			 */
			if (inode) {
				dentry->d_inode = NULL;
				list_del_init(&dentry->d_alias);
				spin_unlock(&dentry->d_lock);
				spin_unlock(&sbi->rehash_lock);
				spin_unlock(&dcache_lock);
				iput(inode);
				return dentry;
			}
			spin_unlock(&dentry->d_lock);
			spin_unlock(&sbi->rehash_lock);
			spin_unlock(&dcache_lock);
			return dentry;
		}
next:
		spin_unlock(&dentry->d_lock);
	}
	spin_unlock(&sbi->rehash_lock);
	spin_unlock(&dcache_lock);

	return NULL;
}

/* Lookups in the root directory */
static struct dentry *autofs4_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
{
	struct autofs_sb_info *sbi;
	struct dentry *unhashed;
	int oz_mode;

	DPRINTK("name = %.*s",
		dentry->d_name.len, dentry->d_name.name);

	/* File name too long to exist */
	if (dentry->d_name.len > NAME_MAX)
		return ERR_PTR(-ENAMETOOLONG);

	sbi = autofs4_sbi(dir->i_sb);
	oz_mode = autofs4_oz_mode(sbi);

	DPRINTK("pid = %u, pgrp = %u, catatonic = %d, oz_mode = %d",
		 current->pid, task_pgrp_nr(current), sbi->catatonic, oz_mode);

	unhashed = autofs4_lookup_unhashed(sbi, dentry->d_parent, &dentry->d_name);
	if (!unhashed) {
		/*
		 * Mark the dentry incomplete but don't hash it. We do this
		 * to serialize our inode creation operations (symlink and
		 * mkdir) which prevents deadlock during the callback to
		 * the daemon. Subsequent user space lookups for the same
		 * dentry are placed on the wait queue while the daemon
		 * itself is allowed passage unresticted so the create
		 * operation itself can then hash the dentry. Finally,
		 * we check for the hashed dentry and return the newly
		 * hashed dentry.
		 */
		dentry->d_op = &autofs4_root_dentry_operations;

		dentry->d_fsdata = NULL;
		d_instantiate(dentry, NULL);
	} else {
		struct autofs_info *ino = autofs4_dentry_ino(unhashed);
		DPRINTK("rehash %p with %p", dentry, unhashed);
		/*
		 * If we are racing with expire the request might not
		 * be quite complete but the directory has been removed
		 * so it must have been successful, so just wait for it.
		 * We need to ensure the AUTOFS_INF_EXPIRING flag is clear
		 * before continuing as revalidate may fail when calling
		 * try_to_fill_dentry (returning EAGAIN) if we don't.
		 */
		while (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
			DPRINTK("wait for incomplete expire %p name=%.*s",
				unhashed, unhashed->d_name.len,
				unhashed->d_name.name);
			autofs4_wait(sbi, unhashed, NFY_NONE);
			DPRINTK("request completed");
		}
		dentry = unhashed;
	}

	if (!oz_mode) {
		spin_lock(&dentry->d_lock);
		dentry->d_flags |= DCACHE_AUTOFS_PENDING;
		spin_unlock(&dentry->d_lock);
	}

	if (dentry->d_op && dentry->d_op->d_revalidate) {
		mutex_unlock(&dir->i_mutex);
		(dentry->d_op->d_revalidate)(dentry, nd);
		mutex_lock(&dir->i_mutex);
	}

	/*
	 * If we are still pending, check if we had to handle
	 * a signal. If so we can force a restart..
	 */
	if (dentry->d_flags & DCACHE_AUTOFS_PENDING) {
		/* See if we were interrupted */
		if (signal_pending(current)) {
			sigset_t *sigset = &current->pending.signal;
			if (sigismember (sigset, SIGKILL) ||
			    sigismember (sigset, SIGQUIT) ||
			    sigismember (sigset, SIGINT)) {
			    if (unhashed)
				dput(unhashed);
			    return ERR_PTR(-ERESTARTNOINTR);
			}
		}
		spin_lock(&dentry->d_lock);
		dentry->d_flags &= ~DCACHE_AUTOFS_PENDING;
		spin_unlock(&dentry->d_lock);
	}

	/*
	 * If this dentry is unhashed, then we shouldn't honour this
	 * lookup.  Returning ENOENT here doesn't do the right thing
	 * for all system calls, but it should be OK for the operations
	 * we permit from an autofs.
	 */
	if (!oz_mode && d_unhashed(dentry)) {
		/*
		 * A user space application can (and has done in the past)
		 * remove and re-create this directory during the callback.
		 * This can leave us with an unhashed dentry, but a
		 * successful mount!  So we need to perform another
		 * cached lookup in case the dentry now exists.
		 */
		struct dentry *parent = dentry->d_parent;
		struct dentry *new = d_lookup(parent, &dentry->d_name);
		if (new != NULL)
			dentry = new;
		else
			dentry = ERR_PTR(-ENOENT);

		if (unhashed)
			dput(unhashed);

		return dentry;
	}

	if (unhashed)
		return dentry;

	return NULL;
}

static int autofs4_dir_symlink(struct inode *dir, 
			       struct dentry *dentry,
			       const char *symname)
{
	struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
	struct autofs_info *ino = autofs4_dentry_ino(dentry);
	struct autofs_info *p_ino;
	struct inode *inode;
	char *cp;

	DPRINTK("%s <- %.*s", symname,
		dentry->d_name.len, dentry->d_name.name);

	if (!autofs4_oz_mode(sbi))
		return -EACCES;

	ino = autofs4_init_ino(ino, sbi, S_IFLNK | 0555);
	if (ino == NULL)
		return -ENOSPC;

	ino->size = strlen(symname);
	ino->u.symlink = cp = kmalloc(ino->size + 1, GFP_KERNEL);

	if (cp == NULL) {
		kfree(ino);
		return -ENOSPC;
	}

	strcpy(cp, symname);

	inode = autofs4_get_inode(dir->i_sb, ino);
	d_add(dentry, inode);

	if (dir == dir->i_sb->s_root->d_inode)
		dentry->d_op = &autofs4_root_dentry_operations;
	else
		dentry->d_op = &autofs4_dentry_operations;

	dentry->d_fsdata = ino;
	ino->dentry = dget(dentry);
	atomic_inc(&ino->count);
	p_ino = autofs4_dentry_ino(dentry->d_parent);
	if (p_ino && dentry->d_parent != dentry)
		atomic_inc(&p_ino->count);
	ino->inode = inode;

	dir->i_mtime = CURRENT_TIME;

	return 0;
}

/*
 * NOTE!
 *
 * Normal filesystems would do a "d_delete()" to tell the VFS dcache
 * that the file no longer exists. However, doing that means that the
 * VFS layer can turn the dentry into a negative dentry.  We don't want
 * this, because the unlink is probably the result of an expire.
 * We simply d_drop it and add it to a rehash candidates list in the
 * super block, which allows the dentry lookup to reuse it retaining
 * the flags, such as expire in progress, in case we're racing with expire.
 *
 * If a process is blocked on the dentry waiting for the expire to finish,
 * it will invalidate the dentry and try to mount with a new one.
 *
 * Also see autofs4_dir_rmdir()..
 */
static int autofs4_dir_unlink(struct inode *dir, struct dentry *dentry)
{
	struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
	struct autofs_info *ino = autofs4_dentry_ino(dentry);
	struct autofs_info *p_ino;
	
	/* This allows root to remove symlinks */
	if (!autofs4_oz_mode(sbi) && !capable(CAP_SYS_ADMIN))
		return -EACCES;

	if (atomic_dec_and_test(&ino->count)) {
		p_ino = autofs4_dentry_ino(dentry->d_parent);
		if (p_ino && dentry->d_parent != dentry)
			atomic_dec(&p_ino->count);
	}
	dput(ino->dentry);

	dentry->d_inode->i_size = 0;
	clear_nlink(dentry->d_inode);

	dir->i_mtime = CURRENT_TIME;

	spin_lock(&dcache_lock);
	spin_lock(&sbi->rehash_lock);
	list_add(&ino->rehash, &sbi->rehash_list);
	spin_unlock(&sbi->rehash_lock);
	spin_lock(&dentry->d_lock);
	__d_drop(dentry);
	spin_unlock(&dentry->d_lock);
	spin_unlock(&dcache_lock);

	return 0;
}

static int autofs4_dir_rmdir(struct inode *dir, struct dentry *dentry)
{
	struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
	struct autofs_info *ino = autofs4_dentry_ino(dentry);
	struct autofs_info *p_ino;
	
	DPRINTK("dentry %p, removing %.*s",
		dentry, dentry->d_name.len, dentry->d_name.name);

	if (!autofs4_oz_mode(sbi))
		return -EACCES;

	spin_lock(&dcache_lock);
	if (!list_empty(&dentry->d_subdirs)) {
		spin_unlock(&dcache_lock);
		return -ENOTEMPTY;
	}
	spin_lock(&sbi->rehash_lock);
	list_add(&ino->rehash, &sbi->rehash_list);
	spin_unlock(&sbi->rehash_lock);
	spin_lock(&dentry->d_lock);
	__d_drop(dentry);
	spin_unlock(&dentry->d_lock);
	spin_unlock(&dcache_lock);

	if (atomic_dec_and_test(&ino->count)) {
		p_ino = autofs4_dentry_ino(dentry->d_parent);
		if (p_ino && dentry->d_parent != dentry)
			atomic_dec(&p_ino->count);
	}
	dput(ino->dentry);
	dentry->d_inode->i_size = 0;
	clear_nlink(dentry->d_inode);

	if (dir->i_nlink)
		drop_nlink(dir);

	return 0;
}

static int autofs4_dir_mkdir(struct inode *dir, struct dentry *dentry, int mode)
{
	struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
	struct autofs_info *ino = autofs4_dentry_ino(dentry);
	struct autofs_info *p_ino;
	struct inode *inode;

	if (!autofs4_oz_mode(sbi))
		return -EACCES;

	DPRINTK("dentry %p, creating %.*s",
		dentry, dentry->d_name.len, dentry->d_name.name);

	ino = autofs4_init_ino(ino, sbi, S_IFDIR | 0555);
	if (ino == NULL)
		return -ENOSPC;

	inode = autofs4_get_inode(dir->i_sb, ino);
	d_add(dentry, inode);

	if (dir == dir->i_sb->s_root->d_inode)
		dentry->d_op = &autofs4_root_dentry_operations;
	else
		dentry->d_op = &autofs4_dentry_operations;

	dentry->d_fsdata = ino;
	ino->dentry = dget(dentry);
	atomic_inc(&ino->count);
	p_ino = autofs4_dentry_ino(dentry->d_parent);
	if (p_ino && dentry->d_parent != dentry)
		atomic_inc(&p_ino->count);
	ino->inode = inode;
	inc_nlink(dir);
	dir->i_mtime = CURRENT_TIME;

	return 0;
}

/* Get/set timeout ioctl() operation */
static inline int autofs4_get_set_timeout(struct autofs_sb_info *sbi,
					 unsigned long __user *p)
{
	int rv;
	unsigned long ntimeout;

	if ((rv = get_user(ntimeout, p)) ||
	     (rv = put_user(sbi->exp_timeout/HZ, p)))
		return rv;

	if (ntimeout > ULONG_MAX/HZ)
		sbi->exp_timeout = 0;
	else
		sbi->exp_timeout = ntimeout * HZ;

	return 0;
}

/* Return protocol version */
static inline int autofs4_get_protover(struct autofs_sb_info *sbi, int __user *p)
{
	return put_user(sbi->version, p);
}

/* Return protocol sub version */
static inline int autofs4_get_protosubver(struct autofs_sb_info *sbi, int __user *p)
{
	return put_user(sbi->sub_version, p);
}

/*
 * Tells the daemon whether we need to reghost or not. Also, clears
 * the reghost_needed flag.
 */
static inline int autofs4_ask_reghost(struct autofs_sb_info *sbi, int __user *p)
{
	int status;

	DPRINTK("returning %d", sbi->needs_reghost);

	status = put_user(sbi->needs_reghost, p);
	if (status)
		return status;

	sbi->needs_reghost = 0;
	return 0;
}

/*
 * Enable / Disable reghosting ioctl() operation
 */
static inline int autofs4_toggle_reghost(struct autofs_sb_info *sbi, int __user *p)
{
	int status;
	int val;

	status = get_user(val, p);

	DPRINTK("reghost = %d", val);

	if (status)
		return status;

	/* turn on/off reghosting, with the val */
	sbi->reghost_enabled = val;
	return 0;
}

/*
* Tells the daemon whether it can umount the autofs mount.
*/
static inline int autofs4_ask_umount(struct vfsmount *mnt, int __user *p)
{
	int status = 0;

	if (may_umount(mnt))
		status = 1;

	DPRINTK("returning %d", status);

	status = put_user(status, p);

	return status;
}

/* Identify autofs4_dentries - this is so we can tell if there's
   an extra dentry refcount or not.  We only hold a refcount on the
   dentry if its non-negative (ie, d_inode != NULL)
*/
int is_autofs4_dentry(struct dentry *dentry)
{
	return dentry && dentry->d_inode &&
		(dentry->d_op == &autofs4_root_dentry_operations ||
		 dentry->d_op == &autofs4_dentry_operations) &&
		dentry->d_fsdata != NULL;
}

/*
 * ioctl()'s on the root directory is the chief method for the daemon to
 * generate kernel reactions
 */
static int autofs4_root_ioctl(struct inode *inode, struct file *filp,
			     unsigned int cmd, unsigned long arg)
{
	struct autofs_sb_info *sbi = autofs4_sbi(inode->i_sb);
	void __user *p = (void __user *)arg;

	DPRINTK("cmd = 0x%08x, arg = 0x%08lx, sbi = %p, pgrp = %u",
		cmd,arg,sbi,task_pgrp_nr(current));

	if (_IOC_TYPE(cmd) != _IOC_TYPE(AUTOFS_IOC_FIRST) ||
	     _IOC_NR(cmd) - _IOC_NR(AUTOFS_IOC_FIRST) >= AUTOFS_IOC_COUNT)
		return -ENOTTY;
	
	if (!autofs4_oz_mode(sbi) && !capable(CAP_SYS_ADMIN))
		return -EPERM;
	
	switch(cmd) {
	case AUTOFS_IOC_READY:	/* Wait queue: go ahead and retry */
		return autofs4_wait_release(sbi,(autofs_wqt_t)arg,0);
	case AUTOFS_IOC_FAIL:	/* Wait queue: fail with ENOENT */
		return autofs4_wait_release(sbi,(autofs_wqt_t)arg,-ENOENT);
	case AUTOFS_IOC_CATATONIC: /* Enter catatonic mode (daemon shutdown) */
		autofs4_catatonic_mode(sbi);
		return 0;
	case AUTOFS_IOC_PROTOVER: /* Get protocol version */
		return autofs4_get_protover(sbi, p);
	case AUTOFS_IOC_PROTOSUBVER: /* Get protocol sub version */
		return autofs4_get_protosubver(sbi, p);
	case AUTOFS_IOC_SETTIMEOUT:
		return autofs4_get_set_timeout(sbi, p);

	case AUTOFS_IOC_TOGGLEREGHOST:
		return autofs4_toggle_reghost(sbi, p);
	case AUTOFS_IOC_ASKREGHOST:
		return autofs4_ask_reghost(sbi, p);

	case AUTOFS_IOC_ASKUMOUNT:
		return autofs4_ask_umount(filp->f_path.mnt, p);

	/* return a single thing to expire */
	case AUTOFS_IOC_EXPIRE:
		return autofs4_expire_run(inode->i_sb,filp->f_path.mnt,sbi, p);
	/* same as above, but can send multiple expires through pipe */
	case AUTOFS_IOC_EXPIRE_MULTI:
		return autofs4_expire_multi(inode->i_sb,filp->f_path.mnt,sbi, p);

	default:
		return -ENOSYS;
	}
}