On Thu, Jul 02, 2020 at 07:56:57AM +0800, Qu Wenruo wrote: > On 2020/7/2 上午1:39, David Sterba wrote: > > On Wed, Jul 01, 2020 at 11:25:27AM +0800, Qu Wenruo wrote: > > Adding the anon_dev argument to btrfs_get_fs_root is wrong and I have > > never suggested that. What I meant is to put the actual id allocation > > to the callers where the subvolume is created, ie only 2 places. > > You mean to extract btrfs_init_fs_root() out of btrfs_get_fs_root()? > > That looks a little risky and I can't find any good solution to make it > more elegant than the current one. I spent more time reading through the get-fs-root functions and the main problem is that btrfs_get_fs_root is doing several things, and it makes a lot of code simple, I certainly want to keep it that way. The idea was to pre-insert the new root (similar to the root item insertion, btrfs_insert_root) and not letting btrfs_get_fs_root call to btrfs_init_fs_info where the anon_bdev allocation happens for all the other non-ioctl cases. Which could be done by factoring out btrfs_init_fs_root from btrfs_get_fs_root. This would allow to extend only btrfs_init_fs_root arguments with the anon_bdev, and keep btrfs_get_fs_root intact. So this is splitting the API from the end. What you originally proposed is a split from the begnning, ie. add a common implementation for existing and new and provide btrfs_get_fs_root and btrfs_get_new_fs_root that would hide the additional parameters. Both ways are IMO valid but I thought it would be easier to pass the anon bdev inside ioctl callbacks. The problem that makes my proposal less appealing is that btrfs_read_tree_root gets called earlier than I'd like so factoring everything after btrfs_init_fs_root would not be so straightforward. In conclusion, your proposal is better and I'm going to merge it. > Although I would definitely remove the "__" prefix as we shouldn't add > such prefix anymore. Yeah with the small naming fixups.
