Btrfs: add SNAP_CREATE_ASYNC ioctl

Create a snap without waiting for it to commit to disk.  The ioctl is
ordered such that subsequent operations will not be contained by the
created snapshot, and the commit is initiated, but the ioctl does not
wait for the snapshot to commit to disk.

We return the specific transid to userspace so that an application can wait
for this specific snapshot creation to commit via the WAIT_SYNC ioctl.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 83 insertions, 24 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index dc5a19ed07f3..e8a26a3aac3e 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -224,7 +224,8 @@ static int btrfs_ioctl_getversion(struct file *file, int __user *arg)
 
 static noinline int create_subvol(struct btrfs_root *root,
 				  struct dentry *dentry,
-				  char *name, int namelen)
+				  char *name, int namelen,
+				  u64 *async_transid)
 {
 	struct btrfs_trans_handle *trans;
 	struct btrfs_key key;
@@ -338,13 +339,19 @@ static noinline int create_subvol(struct btrfs_root *root,
 
 	d_instantiate(dentry, btrfs_lookup_dentry(dir, dentry));
 fail:
-	err = btrfs_commit_transaction(trans, root);
+	if (async_transid) {
+		*async_transid = trans->transid;
+		err = btrfs_commit_transaction_async(trans, root, 1);
+	} else {
+		err = btrfs_commit_transaction(trans, root);
+	}
 	if (err && !ret)
 		ret = err;
 	return ret;
 }
 
-static int create_snapshot(struct btrfs_root *root, struct dentry *dentry)
+static int create_snapshot(struct btrfs_root *root, struct dentry *dentry,
+			   char *name, int namelen, u64 *async_transid)
 {
 	struct inode *inode;
 	struct btrfs_pending_snapshot *pending_snapshot;
@@ -373,7 +380,14 @@ static int create_snapshot(struct btrfs_root *root, struct dentry *dentry)
 
 	list_add(&pending_snapshot->list,
 		 &trans->transaction->pending_snapshots);
-	ret = btrfs_commit_transaction(trans, root->fs_info->extent_root);
+	if (async_transid) {
+		*async_transid = trans->transid;
+		ret = btrfs_commit_transaction_async(trans,
+				     root->fs_info->extent_root, 1);
+	} else {
+		ret = btrfs_commit_transaction(trans,
+					       root->fs_info->extent_root);
+	}
 	BUG_ON(ret);
 
 	ret = pending_snapshot->error;
@@ -412,7 +426,8 @@ static inline int btrfs_may_create(struct inode *dir, struct dentry *child)
  */
 static noinline int btrfs_mksubvol(struct path *parent,
 				   char *name, int namelen,
-				   struct btrfs_root *snap_src)
+				   struct btrfs_root *snap_src,
+				   u64 *async_transid)
 {
 	struct inode *dir  = parent->dentry->d_inode;
 	struct dentry *dentry;
@@ -443,10 +458,11 @@ static noinline int btrfs_mksubvol(struct path *parent,
 		goto out_up_read;
 
 	if (snap_src) {
-		error = create_snapshot(snap_src, dentry);
+		error = create_snapshot(snap_src, dentry,
+					name, namelen, async_transid);
 	} else {
 		error = create_subvol(BTRFS_I(dir)->root, dentry,
-				      name, namelen);
+				      name, namelen, async_transid);
 	}
 	if (!error)
 		fsnotify_mkdir(dir, dentry);
@@ -799,11 +815,13 @@ out_unlock:
 	return ret;
 }
 
-static noinline int btrfs_ioctl_snap_create(struct file *file,
-					    void __user *arg, int subvol)
+static noinline int btrfs_ioctl_snap_create_transid(struct file *file,
+						    char *name,
+						    unsigned long fd,
+						    int subvol,
+						    u64 *transid)
 {
 	struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
-	struct btrfs_ioctl_vol_args *vol_args;
 	struct file *src_file;
 	int namelen;
 	int ret = 0;
@@ -811,23 +829,18 @@ static noinline int btrfs_ioctl_snap_create(struct file *file,
 	if (root->fs_info->sb->s_flags & MS_RDONLY)
 		return -EROFS;
 
-	vol_args = memdup_user(arg, sizeof(*vol_args));
-	if (IS_ERR(vol_args))
-		return PTR_ERR(vol_args);
-
-	vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
-	namelen = strlen(vol_args->name);
-	if (strchr(vol_args->name, '/')) {
+	namelen = strlen(name);
+	if (strchr(name, '/')) {
 		ret = -EINVAL;
 		goto out;
 	}
 
 	if (subvol) {
-		ret = btrfs_mksubvol(&file->f_path, vol_args->name, namelen,
-				     NULL);
+		ret = btrfs_mksubvol(&file->f_path, name, namelen,
+				     NULL, transid);
 	} else {
 		struct inode *src_inode;
-		src_file = fget(vol_args->fd);
+		src_file = fget(fd);
 		if (!src_file) {
 			ret = -EINVAL;
 			goto out;
@@ -841,12 +854,56 @@ static noinline int btrfs_ioctl_snap_create(struct file *file,
 			fput(src_file);
 			goto out;
 		}
-		ret = btrfs_mksubvol(&file->f_path, vol_args->name, namelen,
-				     BTRFS_I(src_inode)->root);
+		ret = btrfs_mksubvol(&file->f_path, name, namelen,
+				     BTRFS_I(src_inode)->root,
+				     transid);
 		fput(src_file);
 	}
 out:
+	return ret;
+}
+
+static noinline int btrfs_ioctl_snap_create(struct file *file,
+					    void __user *arg, int subvol,
+					    int async)
+{
+	struct btrfs_ioctl_vol_args *vol_args = NULL;
+	struct btrfs_ioctl_async_vol_args *async_vol_args = NULL;
+	char *name;
+	u64 fd;
+	u64 transid = 0;
+	int ret;
+
+	if (async) {
+		async_vol_args = memdup_user(arg, sizeof(*async_vol_args));
+		if (IS_ERR(async_vol_args))
+			return PTR_ERR(async_vol_args);
+
+		name = async_vol_args->name;
+		fd = async_vol_args->fd;
+		async_vol_args->name[BTRFS_SNAPSHOT_NAME_MAX] = '\0';
+	} else {
+		vol_args = memdup_user(arg, sizeof(*vol_args));
+		if (IS_ERR(vol_args))
+			return PTR_ERR(vol_args);
+		name = vol_args->name;
+		fd = vol_args->fd;
+		vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
+	}
+
+	ret = btrfs_ioctl_snap_create_transid(file, name, fd,
+					      subvol, &transid);
+
+	if (!ret && async) {
+		if (copy_to_user(arg +
+				offsetof(struct btrfs_ioctl_async_vol_args,
+				transid), &transid, sizeof(transid)))
+			return -EFAULT;
+	}
+
 	kfree(vol_args);
+	kfree(async_vol_args);
+
 	return ret;
 }
 
@@ -2072,9 +2129,11 @@ long btrfs_ioctl(struct file *file, unsigned int
 	case FS_IOC_GETVERSION:
 		return btrfs_ioctl_getversion(file, argp);
 	case BTRFS_IOC_SNAP_CREATE:
-		return btrfs_ioctl_snap_create(file, argp, 0);
+		return btrfs_ioctl_snap_create(file, argp, 0, 0);
+	case BTRFS_IOC_SNAP_CREATE_ASYNC:
+		return btrfs_ioctl_snap_create(file, argp, 0, 1);
 	case BTRFS_IOC_SUBVOL_CREATE:
-		return btrfs_ioctl_snap_create(file, argp, 1);
+		return btrfs_ioctl_snap_create(file, argp, 1, 0);
 	case BTRFS_IOC_SNAP_DESTROY:
 		return btrfs_ioctl_snap_destroy(file, argp);
 	case BTRFS_IOC_DEFAULT_SUBVOL: