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Commit 451d0f59 authored by John Muir's avatar John Muir Committed by Miklos Szeredi
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FUSE: Notifying the kernel of deletion. 



Allows a FUSE file-system to tell the kernel when a file or directory is
deleted. If the specified dentry has the specified inode number, the kernel will
unhash it.

The current 'fuse_notify_inval_entry' does not cause the kernel to clean up
directories that are in use properly, and as a result the users of those
directories see incorrect semantics from the file-system. The error condition
seen when 'fuse_notify_inval_entry' is used to notify of a deleted directory is
avoided when 'fuse_notify_delete' is used instead.

The following scenario demonstrates the difference:
1. User A chdirs into 'testdir' and starts reading 'testfile'.
2. User B rm -rf 'testdir'.
3. User B creates 'testdir'.
4. User C chdirs into 'testdir'.

If you run the above within the same machine on any file-system (including fuse
file-systems), there is no problem: user C is able to chdir into the new
testdir. The old testdir is removed from the dentry tree, but still open by user
A.

If operations 2 and 3 are performed via the network such that the fuse
file-system uses one of the notify functions to tell the kernel that the nodes
are gone, then the following error occurs for user C while user A holds the
original directory open:

muirj@empacher:~> ls /test/testdir
ls: cannot access /test/testdir: No such file or directory

The issue here is that the kernel still has a dentry for testdir, and so it is
requesting the attributes for the old directory, while the file-system is
responding that the directory no longer exists.

If on the other hand, if the file-system can notify the kernel that the
directory is deleted using the new 'fuse_notify_delete' function, then the above
ls will find the new directory as expected.

Signed-off-by: default avatarJohn Muir <john@jmuir.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@suse.cz>
parent b18da0c5

fs/fuse/dev.c

+56 −1
Original line number Diff line number Diff line
@@ -1378,7 +1378,59 @@ static int fuse_notify_inval_entry(struct fuse_conn *fc, unsigned int size, 
	down_read(&fc->killsb);

	err = -ENOENT;

	if (fc->sb)

		err = fuse_reverse_inval_entry(fc->sb, outarg.parent, &name);

		err = fuse_reverse_inval_entry(fc->sb, outarg.parent, 0, &name);

	up_read(&fc->killsb);

	kfree(buf);

	return err;



err:

	kfree(buf);

	fuse_copy_finish(cs);

	return err;

}



static int fuse_notify_delete(struct fuse_conn *fc, unsigned int size,

			      struct fuse_copy_state *cs)

{

	struct fuse_notify_delete_out outarg;

	int err = -ENOMEM;

	char *buf;

	struct qstr name;



	buf = kzalloc(FUSE_NAME_MAX + 1, GFP_KERNEL);

	if (!buf)

		goto err;



	err = -EINVAL;

	if (size < sizeof(outarg))

		goto err;



	err = fuse_copy_one(cs, &outarg, sizeof(outarg));

	if (err)

		goto err;



	err = -ENAMETOOLONG;

	if (outarg.namelen > FUSE_NAME_MAX)

		goto err;



	err = -EINVAL;

	if (size != sizeof(outarg) + outarg.namelen + 1)

		goto err;



	name.name = buf;

	name.len = outarg.namelen;

	err = fuse_copy_one(cs, buf, outarg.namelen + 1);

	if (err)

		goto err;

	fuse_copy_finish(cs);

	buf[outarg.namelen] = 0;

	name.hash = full_name_hash(name.name, name.len);



	down_read(&fc->killsb);

	err = -ENOENT;

	if (fc->sb)

		err = fuse_reverse_inval_entry(fc->sb, outarg.parent,

					       outarg.child, &name);

	up_read(&fc->killsb);

	kfree(buf);

	return err;
@@ -1597,6 +1649,9 @@ static int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code, 
	case FUSE_NOTIFY_RETRIEVE:

		return fuse_notify_retrieve(fc, size, cs);



	case FUSE_NOTIFY_DELETE:

		return fuse_notify_delete(fc, size, cs);



	default:

		fuse_copy_finish(cs);

		return -EINVAL;

fs/fuse/dir.c

+30 −2
Original line number Diff line number Diff line
@@ -868,7 +868,7 @@ int fuse_update_attributes(struct inode *inode, struct kstat *stat, 
}



int fuse_reverse_inval_entry(struct super_block *sb, u64 parent_nodeid,

			     struct qstr *name)

			     u64 child_nodeid, struct qstr *name)

{

	int err = -ENOTDIR;

	struct inode *parent;
@@ -895,8 +895,36 @@ int fuse_reverse_inval_entry(struct super_block *sb, u64 parent_nodeid, 


	fuse_invalidate_attr(parent);

	fuse_invalidate_entry(entry);

	dput(entry);



	if (child_nodeid != 0 && entry->d_inode) {

		mutex_lock(&entry->d_inode->i_mutex);

		if (get_node_id(entry->d_inode) != child_nodeid) {

			err = -ENOENT;

			goto badentry;

		}

		if (d_mountpoint(entry)) {

			err = -EBUSY;

			goto badentry;

		}

		if (S_ISDIR(entry->d_inode->i_mode)) {

			shrink_dcache_parent(entry);

			if (!simple_empty(entry)) {

				err = -ENOTEMPTY;

				goto badentry;

			}

			entry->d_inode->i_flags |= S_DEAD;

		}

		dont_mount(entry);

		clear_nlink(entry->d_inode);

		err = 0;

 badentry:

		mutex_unlock(&entry->d_inode->i_mutex);

		if (!err)

			d_delete(entry);

	} else {

		err = 0;

	}

	dput(entry);



 unlock:

	mutex_unlock(&parent->i_mutex);

fs/fuse/fuse_i.h

+7 −1
Original line number Diff line number Diff line
@@ -755,9 +755,15 @@ int fuse_reverse_inval_inode(struct super_block *sb, u64 nodeid, 
/**

 * File-system tells the kernel to invalidate parent attributes and

 * the dentry matching parent/name.

 *

 * If the child_nodeid is non-zero and:

 *    - matches the inode number for the dentry matching parent/name,

 *    - is not a mount point

 *    - is a file or oan empty directory

 * then the dentry is unhashed (d_delete()).

 */

int fuse_reverse_inval_entry(struct super_block *sb, u64 parent_nodeid,

			     struct qstr *name);

			     u64 child_nodeid, struct qstr *name);



int fuse_do_open(struct fuse_conn *fc, u64 nodeid, struct file *file,

		 bool isdir);

include/linux/fuse.h

+9 −0
Original line number Diff line number Diff line
@@ -53,6 +53,7 @@ 
 *

 * 7.18

 *  - add FUSE_IOCTL_DIR flag

 *  - add FUSE_NOTIFY_DELETE

 */



#ifndef _LINUX_FUSE_H
@@ -288,6 +289,7 @@ enum fuse_notify_code { 
	FUSE_NOTIFY_INVAL_ENTRY = 3,

	FUSE_NOTIFY_STORE = 4,

	FUSE_NOTIFY_RETRIEVE = 5,

	FUSE_NOTIFY_DELETE = 6,

	FUSE_NOTIFY_CODE_MAX,

};
@@ -611,6 +613,13 @@ struct fuse_notify_inval_entry_out { 
	__u32	padding;

};



struct fuse_notify_delete_out {

	__u64	parent;

	__u64	child;

	__u32	namelen;

	__u32	padding;

};



struct fuse_notify_store_out {

	__u64	nodeid;

	__u64	offset;