Commit 6bf13c0c authored by Sage Weil's avatar Sage Weil Committed by Chris Mason
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Btrfs: transaction ioctls 



These ioctls let a user application hold a transaction open while it
performs a series of operations.  A final ioctl does a sync on the fs
(closing the current transaction).  This is the main requirement for
Ceph's OSD to be able to keep the data it's storing in a btrfs volume
consistent, and AFAICS it works just fine.  The application would do
something like

	fd = ::open("some/file", O_RDONLY);
	::ioctl(fd, BTRFS_IOC_TRANS_START);
	/* do a bunch of stuff */
	::ioctl(fd, BTRFS_IOC_TRANS_END);
or just
	::close(fd);

And to ensure it commits to disk,

	::ioctl(fd, BTRFS_IOC_SYNC);

When a transaction is held open, the trans_handle is attached to the
struct file (via private_data) so that it will get cleaned up if the
process dies unexpectedly.  A held transaction is also ended on fsync() to
avoid a deadlock.

A misbehaving application could also deliberately hold a transaction open,
effectively locking up the FS, so it may make sense to restrict something
like this to root or something.

Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent eba12c7b

fs/btrfs/ctree.h

+4 −0
Original line number Diff line number Diff line
@@ -1575,6 +1575,7 @@ struct inode *btrfs_alloc_inode(struct super_block *sb); 
void btrfs_destroy_inode(struct inode *inode);

int btrfs_init_cachep(void);

void btrfs_destroy_cachep(void);

long btrfs_ioctl_trans_end(struct file *file);

long btrfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);

struct inode *btrfs_iget_locked(struct super_block *s, u64 objectid,

				struct btrfs_root *root);
@@ -1595,6 +1596,8 @@ extern struct file_operations btrfs_file_operations; 
int btrfs_drop_extents(struct btrfs_trans_handle *trans,

		       struct btrfs_root *root, struct inode *inode,

		       u64 start, u64 end, u64 inline_limit, u64 *hint_block);

int btrfs_release_file(struct inode *inode, struct file *file);



/* tree-defrag.c */

int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,

			struct btrfs_root *root, int cache_only);
@@ -1615,4 +1618,5 @@ int btrfs_delete_xattrs(struct btrfs_trans_handle *trans, 
u64 btrfs_parse_size(char *str);

int btrfs_parse_options(char *options, struct btrfs_root *root,

			char **subvol_name);

int btrfs_sync_fs(struct super_block *sb, int wait);

#endif

fs/btrfs/file.c

+6 −1
Original line number Diff line number Diff line
@@ -978,9 +978,11 @@ out_nolock: 
	return num_written ? num_written : err;

}



static int btrfs_release_file (struct inode * inode, struct file * filp)

int btrfs_release_file(struct inode * inode, struct file * filp)

{

	btrfs_del_ordered_inode(inode);

	if (filp->private_data)

		btrfs_ioctl_trans_end(filp);

	return 0;

}
@@ -1011,6 +1013,9 @@ static int btrfs_sync_file(struct file *file, 
	/*

	 * ok we haven't committed the transaction yet, lets do a commit

	 */

	if (file->private_data)

		btrfs_ioctl_trans_end(file);



	trans = btrfs_start_transaction(root, 1);

	if (!trans) {

		ret = -ENOMEM;

fs/btrfs/inode.c

+63 −0
Original line number Diff line number Diff line
@@ -3336,6 +3336,61 @@ out_fput: 
	return ret;

}



/*

 * there are many ways the trans_start and trans_end ioctls can lead

 * to deadlocks.  They should only be used by applications that

 * basically own the machine, and have a very in depth understanding

 * of all the possible deadlocks and enospc problems.

 */

long btrfs_ioctl_trans_start(struct file *file)

{

	struct inode *inode = fdentry(file)->d_inode;

	struct btrfs_root *root = BTRFS_I(inode)->root;

	struct btrfs_trans_handle *trans;

	int ret = 0;



	mutex_lock(&root->fs_info->fs_mutex);

	if (file->private_data) {

		ret = -EINPROGRESS;

		goto out;

	}

	trans = btrfs_start_transaction(root, 0);

	if (trans)

		file->private_data = trans;

	else

		ret = -ENOMEM;

	/*printk(KERN_INFO "btrfs_ioctl_trans_start on %p\n", file);*/

out:

	mutex_unlock(&root->fs_info->fs_mutex);

	return ret;

}



/*

 * there are many ways the trans_start and trans_end ioctls can lead

 * to deadlocks.  They should only be used by applications that

 * basically own the machine, and have a very in depth understanding

 * of all the possible deadlocks and enospc problems.

 */

long btrfs_ioctl_trans_end(struct file *file)

{

	struct inode *inode = fdentry(file)->d_inode;

	struct btrfs_root *root = BTRFS_I(inode)->root;

	struct btrfs_trans_handle *trans;

	int ret = 0;



	mutex_lock(&root->fs_info->fs_mutex);

	trans = file->private_data;

	if (!trans) {

		ret = -EINVAL;

		goto out;

	}

	btrfs_end_transaction(trans, root);

	file->private_data = 0;

out:

	mutex_unlock(&root->fs_info->fs_mutex);

	return ret;

}



long btrfs_ioctl(struct file *file, unsigned int

		cmd, unsigned long arg)

{
@@ -3356,6 +3411,13 @@ long btrfs_ioctl(struct file *file, unsigned int 
		return btrfs_balance(root->fs_info->dev_root);

	case BTRFS_IOC_CLONE:

		return btrfs_ioctl_clone(file, arg);

	case BTRFS_IOC_TRANS_START:

		return btrfs_ioctl_trans_start(file);

	case BTRFS_IOC_TRANS_END:

		return btrfs_ioctl_trans_end(file);

	case BTRFS_IOC_SYNC:

		btrfs_sync_fs(file->f_dentry->d_sb, 1);

		return 0;

	}



	return -ENOTTY;
@@ -3679,6 +3741,7 @@ static struct file_operations btrfs_dir_file_operations = { 
#ifdef CONFIG_COMPAT

	.compat_ioctl	= btrfs_ioctl,

#endif

	.release        = btrfs_release_file,

};



static struct extent_io_ops btrfs_extent_io_ops = {

fs/btrfs/ioctl.h

+9 −0
Original line number Diff line number Diff line
@@ -36,6 +36,14 @@ struct btrfs_ioctl_vol_args { 
				   struct btrfs_ioctl_vol_args)

#define BTRFS_IOC_SCAN_DEV _IOW(BTRFS_IOCTL_MAGIC, 4, \

				   struct btrfs_ioctl_vol_args)

/* trans start and trans end are dangerous, and only for

 * use by applications that know how to avoid the

 * resulting deadlocks

 */

#define BTRFS_IOC_TRANS_START  _IO(BTRFS_IOCTL_MAGIC, 6)

#define BTRFS_IOC_TRANS_END    _IO(BTRFS_IOCTL_MAGIC, 7)

#define BTRFS_IOC_SYNC         _IO(BTRFS_IOCTL_MAGIC, 8)



#define BTRFS_IOC_CLONE        _IOW(BTRFS_IOCTL_MAGIC, 9, int)

#define BTRFS_IOC_ADD_DEV _IOW(BTRFS_IOCTL_MAGIC, 10, \

				   struct btrfs_ioctl_vol_args)
@@ -43,4 +51,5 @@ struct btrfs_ioctl_vol_args { 
				   struct btrfs_ioctl_vol_args)

#define BTRFS_IOC_BALANCE _IOW(BTRFS_IOCTL_MAGIC, 12, \

				   struct btrfs_ioctl_vol_args)



#endif

fs/btrfs/super.c

+1 −1
Original line number Diff line number Diff line
@@ -293,7 +293,7 @@ fail_close: 
	return err;

}



static int btrfs_sync_fs(struct super_block *sb, int wait)

int btrfs_sync_fs(struct super_block *sb, int wait)

{

	struct btrfs_trans_handle *trans;

	struct btrfs_root *root;

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