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>

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 @@ static noinline int btrfs_ioctl_resize(struct btrfs_root *root,
 	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:

fs/btrfs/ioctl.h

@@ -22,14 +22,21 @@
 
 #define BTRFS_IOCTL_MAGIC 0x94
 #define BTRFS_VOL_NAME_MAX 255
-#define BTRFS_PATH_NAME_MAX 4087
 
 /* this should be 4k */
+#define BTRFS_PATH_NAME_MAX 4087
 struct btrfs_ioctl_vol_args {
 	__s64 fd;
 	char name[BTRFS_PATH_NAME_MAX + 1];
 };
 
+#define BTRFS_SNAPSHOT_NAME_MAX 4079
+struct btrfs_ioctl_async_vol_args {
+	__s64 fd;
+	__u64 transid;
+	char name[BTRFS_SNAPSHOT_NAME_MAX + 1];
+};
+
 #define BTRFS_INO_LOOKUP_PATH_MAX 4080
 struct btrfs_ioctl_ino_lookup_args {
 	__u64 treeid;
@@ -180,4 +187,6 @@ struct btrfs_ioctl_space_args {
 				    struct btrfs_ioctl_space_args)
 #define BTRFS_IOC_START_SYNC _IOR(BTRFS_IOCTL_MAGIC, 24, __u64)
 #define BTRFS_IOC_WAIT_SYNC  _IOW(BTRFS_IOCTL_MAGIC, 22, __u64)
+#define BTRFS_IOC_SNAP_CREATE_ASYNC _IOW(BTRFS_IOCTL_MAGIC, 23, \
+				   struct btrfs_ioctl_async_vol_args)
 #endif