[RFC] Btrfs: add ioctl to set the default mount subvol

[RFC] Btrfs: add ioctl to set the default mount subvol

[Josef Bacik]

This patch needs to go along with my previous patch.  This lets us set the
default dir item's location to whatever root we want to use as our default
mounting subvol.  With this we don't have to use mount -o subvol=<tree id>
anymore to mount a different subvol, we can just set the new one and it will
just magically work.  I've just done some superficial testing on this, but it
works well enough.  It breaks the snapshot listing thing so don't try and use
that with this patch, I will fix that later, I just want to run this by
everybody to make sure this is what we want.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
---
 fs/btrfs/ioctl.c |   64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/ioctl.h |    2 +
 2 files changed, 66 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index c157eb7..9b747a9 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1551,6 +1551,68 @@ out:
 	return ret;
 }
 
+static long btrfs_ioctl_default_subvol(struct file *file, void __user *argp)
+{
+	struct inode *inode = fdentry(file)->d_inode;
+	struct btrfs_root *root = BTRFS_I(inode)->root;
+	struct btrfs_root *new_root;
+	struct btrfs_dir_item *di;
+	struct btrfs_trans_handle *trans;
+	struct btrfs_path *path;
+	struct btrfs_key location;
+	struct btrfs_disk_key disk_key;
+	u64 objectid = 0;
+	u64 dir_id;
+
+	if (copy_from_user(&objectid, argp, sizeof(objectid)))
+		return -EFAULT;
+
+	if (!objectid)
+		objectid = root->root_key.objectid;
+
+	location.objectid = objectid;
+	location.type = BTRFS_ROOT_ITEM_KEY;
+	location.offset = (u64)-1;
+
+	new_root = btrfs_read_fs_root_no_name(root->fs_info, &location);
+	if (IS_ERR(new_root))
+		return PTR_ERR(new_root);
+
+	if (btrfs_root_refs(&new_root->root_item) == 0)
+		return -ENOENT;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+	path->leave_spinning = 1;
+
+	trans = btrfs_start_transaction(root, 1);
+	if (!trans) {
+		btrfs_free_path(path);
+		return -ENOMEM;
+	}
+
+	dir_id = btrfs_super_root_dir(&root->fs_info->super_copy);
+	di = btrfs_lookup_dir_item(trans, root->fs_info->tree_root, path,
+				   dir_id, "default", 7, 1);
+	if (!di) {
+		btrfs_free_path(path);
+		btrfs_end_transaction(trans, root);
+		printk(KERN_ERR "Umm, you don't have the default dir item, "
+		       "this isn't going to work\n");
+		return -ENOENT;
+	}
+
+	btrfs_cpu_key_to_disk(&disk_key, &new_root->root_key);
+	btrfs_set_dir_item_key(path->nodes[0], di, &disk_key);
+	btrfs_mark_buffer_dirty(path->nodes[0]);
+	btrfs_free_path(path);
+
+	btrfs_end_transaction(trans, root);
+
+	return 0;
+}
+
 /*
  * there are many ways the trans_start and trans_end ioctls can lead
  * to deadlocks.  They should only be used by applications that
@@ -1597,6 +1659,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_snap_create(file, argp, 1);
 	case BTRFS_IOC_SNAP_DESTROY:
 		return btrfs_ioctl_snap_destroy(file, argp);
+	case BTRFS_IOC_DEFAULT_SUBVOL:
+		return btrfs_ioctl_default_subvol(file, argp);
 	case BTRFS_IOC_DEFRAG:
 		return btrfs_ioctl_defrag(file);
 	case BTRFS_IOC_RESIZE:
diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index 18c554b..9e5074c 100644
--- a/fs/btrfs/ioctl.h
+++ b/fs/btrfs/ioctl.h
@@ -96,4 +96,6 @@ struct btrfs_ioctl_clone_range_args {
 				struct btrfs_ioctl_vol_args)
 #define BTRFS_IOC_SNAP_LISTING _IOWR(BTRFS_IOCTL_MAGIC, 16, \
 				   struct btrfs_ioctl_subvol_args)
+#define BTRFS_IOC_DEFAULT_SUBVOL _IOW(BTRFS_IOCTL_MAGIC, 17, u64)
+
 #endif
-- 
1.5.4.3

Re: [RFC] Btrfs: add ioctl to set the default mount subvol

[TARUISI Hiroaki]

Hi, Josef.

 Thank you for your considering listing patch.
 For now, snapshot listing starts with mounted directory,
but I thought listing by subvol id is needed, considering
'subvol' option (and now, your patch).
 I made a 'subvol id' patch, but if you have another idea,
could you tell me?

Regards,
taruisi

Josef Bacik wrote:
> This patch needs to go along with my previous patch.  This lets us set the
> default dir item's location to whatever root we want to use as our default
> mounting subvol.  With this we don't have to use mount -o subvol=<tree id>
> anymore to mount a different subvol, we can just set the new one and it will
> just magically work.  I've just done some superficial testing on this, but it
> works well enough.  It breaks the snapshot listing thing so don't try and use
> that with this patch, I will fix that later, I just want to run this by
> everybody to make sure this is what we want.  Thanks,
> 
> Signed-off-by: Josef Bacik <josef@redhat.com>
> ---
>  fs/btrfs/ioctl.c |   64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  fs/btrfs/ioctl.h |    2 +
>  2 files changed, 66 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index c157eb7..9b747a9 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -1551,6 +1551,68 @@ out:
>  	return ret;
>  }
>  
> +static long btrfs_ioctl_default_subvol(struct file *file, void __user *argp)
> +{
> +	struct inode *inode = fdentry(file)->d_inode;
> +	struct btrfs_root *root = BTRFS_I(inode)->root;
> +	struct btrfs_root *new_root;
> +	struct btrfs_dir_item *di;
> +	struct btrfs_trans_handle *trans;
> +	struct btrfs_path *path;
> +	struct btrfs_key location;
> +	struct btrfs_disk_key disk_key;
> +	u64 objectid = 0;
> +	u64 dir_id;
> +
> +	if (copy_from_user(&objectid, argp, sizeof(objectid)))
> +		return -EFAULT;
> +
> +	if (!objectid)
> +		objectid = root->root_key.objectid;
> +
> +	location.objectid = objectid;
> +	location.type = BTRFS_ROOT_ITEM_KEY;
> +	location.offset = (u64)-1;
> +
> +	new_root = btrfs_read_fs_root_no_name(root->fs_info, &location);
> +	if (IS_ERR(new_root))
> +		return PTR_ERR(new_root);
> +
> +	if (btrfs_root_refs(&new_root->root_item) == 0)
> +		return -ENOENT;
> +
> +	path = btrfs_alloc_path();
> +	if (!path)
> +		return -ENOMEM;
> +	path->leave_spinning = 1;
> +
> +	trans = btrfs_start_transaction(root, 1);
> +	if (!trans) {
> +		btrfs_free_path(path);
> +		return -ENOMEM;
> +	}
> +
> +	dir_id = btrfs_super_root_dir(&root->fs_info->super_copy);
> +	di = btrfs_lookup_dir_item(trans, root->fs_info->tree_root, path,
> +				   dir_id, "default", 7, 1);
> +	if (!di) {
> +		btrfs_free_path(path);
> +		btrfs_end_transaction(trans, root);
> +		printk(KERN_ERR "Umm, you don't have the default dir item, "
> +		       "this isn't going to work\n");
> +		return -ENOENT;
> +	}
> +
> +	btrfs_cpu_key_to_disk(&disk_key, &new_root->root_key);
> +	btrfs_set_dir_item_key(path->nodes[0], di, &disk_key);
> +	btrfs_mark_buffer_dirty(path->nodes[0]);
> +	btrfs_free_path(path);
> +
> +	btrfs_end_transaction(trans, root);
> +
> +	return 0;
> +}
> +
>  /*
>   * there are many ways the trans_start and trans_end ioctls can lead
>   * to deadlocks.  They should only be used by applications that
> @@ -1597,6 +1659,8 @@ long btrfs_ioctl(struct file *file, unsigned int
>  		return btrfs_ioctl_snap_create(file, argp, 1);
>  	case BTRFS_IOC_SNAP_DESTROY:
>  		return btrfs_ioctl_snap_destroy(file, argp);
> +	case BTRFS_IOC_DEFAULT_SUBVOL:
> +		return btrfs_ioctl_default_subvol(file, argp);
>  	case BTRFS_IOC_DEFRAG:
>  		return btrfs_ioctl_defrag(file);
>  	case BTRFS_IOC_RESIZE:
> diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
> index 18c554b..9e5074c 100644
> --- a/fs/btrfs/ioctl.h
> +++ b/fs/btrfs/ioctl.h
> @@ -96,4 +96,6 @@ struct btrfs_ioctl_clone_range_args {
>  				struct btrfs_ioctl_vol_args)
>  #define BTRFS_IOC_SNAP_LISTING _IOWR(BTRFS_IOCTL_MAGIC, 16, \
>  				   struct btrfs_ioctl_subvol_args)
> +#define BTRFS_IOC_DEFAULT_SUBVOL _IOW(BTRFS_IOCTL_MAGIC, 17, u64)
> +
>  #endif


-- 
taruisi