Re: [PATCH 5/5] btrfs: Switch seed device to list api

[Nikolay Borisov <nborisov@suse.com>]

On 15.07.20 г. 13:48 ч., Nikolay Borisov wrote:
> While this patch touches a bunch of files the conversion is
> straighforward. Instead of using the implicit linked list anchored at
> btrfs_fs_devices::seed the code is switched to using
> list_for_each_entry. Previous patches in the series already factored out
> code that processed both main and seed devices so in those cases
> the factored out functions are called on the main fs_devices and then
> on every seed dev inside list_for_each_entry.
> 
> Using list api also allows to simplify deletion from the seed dev list
> performed in btrfs_rm_device and btrfs_rm_dev_replace_free_srcdev by
> substituting a while() loop with a simple list_del_init.
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>

<snip>

> @@ -6728,8 +6718,8 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,
>  		goto out;
>  	}
>  
> -	fs_devices->seed = fs_info->fs_devices->seed;
> -	fs_info->fs_devices->seed = fs_devices;
> +	ASSERT(list_empty(&fs_devices->seed_list));

That assert is useless, since fs_devices at this point are a clone from
clone_fs_devices hence its seed_list cannot be non-empty. Consider this
when removing merging it.

> +	list_add_tail(&fs_devices->seed_list, &fs_info->fs_devices->seed_list);
>  out:
>  	return fs_devices;
>  }
> @@ -7141,17 +7131,23 @@ int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info)
>  
>  void btrfs_init_devices_late(struct btrfs_fs_info *fs_info)
>  {
> -	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
> +	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices, *seed_devs;
>  	struct btrfs_device *device;
>  
> -	while (fs_devices) {
> -		mutex_lock(&fs_devices->device_list_mutex);
> -		list_for_each_entry(device, &fs_devices->devices, dev_list)
> +	fs_devices->fs_info = fs_info;
> +
> +	mutex_lock(&fs_devices->device_list_mutex);
> +	list_for_each_entry(device, &fs_devices->devices, dev_list)
> +		device->fs_info = fs_info;
> +	mutex_unlock(&fs_devices->device_list_mutex);
> +
> +	list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
> +		mutex_lock(&seed_devs->device_list_mutex);
> +		list_for_each_entry(device, &seed_devs->devices, dev_list)
>  			device->fs_info = fs_info;
> -		mutex_unlock(&fs_devices->device_list_mutex);
> +		mutex_unlock(&seed_devs->device_list_mutex);
>  
> -		fs_devices->fs_info = fs_info;
> -		fs_devices = fs_devices->seed;
> +		seed_devs->fs_info = fs_info;
>  	}
>  }
>  
> @@ -7527,8 +7523,10 @@ static int verify_one_dev_extent(struct btrfs_fs_info *fs_info,
>  
>  	/* It's possible this device is a dummy for seed device */
>  	if (dev->disk_total_bytes == 0) {
> -		dev = btrfs_find_device(fs_info->fs_devices->seed, devid, NULL,
> -					NULL, false);
> +		struct btrfs_fs_devices *devs;
> +		devs = list_first_entry(&fs_info->fs_devices->seed_list,
> +					struct btrfs_fs_devices, seed_list);
> +		dev = btrfs_find_device(devs, devid, NULL, NULL, false);
>  		if (!dev) {
>  			btrfs_err(fs_info, "failed to find seed devid %llu",
>  				  devid);
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index fc283fdbcece..709f4aacbd3f 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -246,7 +246,7 @@ struct btrfs_fs_devices {
>  	 */
>  	struct list_head alloc_list;
>  
> -	struct btrfs_fs_devices *seed;
> +	struct list_head seed_list;
>  	bool seeding;
>  
>  	int opened;
>