Re: [PATCH 1/8] block: make the block holder code optional

[Mike Snitzer <snitzer@redhat.com>]

On Sun, Jul 25 2021 at  1:54P -0400,
Christoph Hellwig <hch@lst.de> wrote:

> Move the block holder code into a separate file as it is not in any way
> related to the other block_dev.c code, and add a new selectable config
> option for it so that we don't have to build it without any remapped
> drivers selected.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  block/Kconfig             |   4 ++
>  block/Makefile            |   1 +
>  block/holder.c            | 139 ++++++++++++++++++++++++++++++++++++
>  drivers/md/Kconfig        |   2 +
>  drivers/md/bcache/Kconfig |   1 +
>  fs/block_dev.c            | 144 +-------------------------------------
>  include/linux/blk_types.h |   2 +-
>  include/linux/genhd.h     |   4 +-
>  8 files changed, 151 insertions(+), 146 deletions(-)
>  create mode 100644 block/holder.c
> 
> diff --git a/block/Kconfig b/block/Kconfig
> index fd732aede922..a24d7263d1fc 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -251,4 +251,8 @@ config BLK_MQ_RDMA
>  config BLK_PM
>  	def_bool BLOCK && PM
>  
> +# do not use in new code
> +config BLOCK_HOLDER_DEPRECATED
> +	bool
> +

What is it that new code that does IO remapping and device stacking
_should_ be using!?  Seems the whole "do not use" and "DEPRECATED" is
a misnomer.

But those nits aside, code looks fine mechnically:

Reviewed-by: Mike Snitzer <snitzer@redhat.com>

>  source "block/Kconfig.iosched"
> diff --git a/block/Makefile b/block/Makefile
> index bfbe4e13ca1e..6fc6216634ed 100644
> --- a/block/Makefile
> +++ b/block/Makefile
> @@ -42,3 +42,4 @@ obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o
>  obj-$(CONFIG_BLK_PM)		+= blk-pm.o
>  obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= keyslot-manager.o blk-crypto.o
>  obj-$(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK)	+= blk-crypto-fallback.o
> +obj-$(CONFIG_BLOCK_HOLDER_DEPRECATED)	+= holder.o
> diff --git a/block/holder.c b/block/holder.c
> new file mode 100644
> index 000000000000..904a1dcd5c12
> --- /dev/null
> +++ b/block/holder.c
> @@ -0,0 +1,139 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <linux/genhd.h>
> +
> +struct bd_holder_disk {
> +	struct list_head	list;
> +	struct gendisk		*disk;
> +	int			refcnt;
> +};
> +
> +static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
> +						  struct gendisk *disk)
> +{
> +	struct bd_holder_disk *holder;
> +
> +	list_for_each_entry(holder, &bdev->bd_holder_disks, list)
> +		if (holder->disk == disk)
> +			return holder;
> +	return NULL;
> +}
> +
> +static int add_symlink(struct kobject *from, struct kobject *to)
> +{
> +	return sysfs_create_link(from, to, kobject_name(to));
> +}
> +
> +static void del_symlink(struct kobject *from, struct kobject *to)
> +{
> +	sysfs_remove_link(from, kobject_name(to));
> +}
> +
> +/**
> + * bd_link_disk_holder - create symlinks between holding disk and slave bdev
> + * @bdev: the claimed slave bdev
> + * @disk: the holding disk
> + *
> + * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
> + *
> + * This functions creates the following sysfs symlinks.
> + *
> + * - from "slaves" directory of the holder @disk to the claimed @bdev
> + * - from "holders" directory of the @bdev to the holder @disk
> + *
> + * For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is
> + * passed to bd_link_disk_holder(), then:
> + *
> + *   /sys/block/dm-0/slaves/sda --> /sys/block/sda
> + *   /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
> + *
> + * The caller must have claimed @bdev before calling this function and
> + * ensure that both @bdev and @disk are valid during the creation and
> + * lifetime of these symlinks.
> + *
> + * CONTEXT:
> + * Might sleep.
> + *
> + * RETURNS:
> + * 0 on success, -errno on failure.
> + */
> +int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
> +{
> +	struct bd_holder_disk *holder;
> +	int ret = 0;
> +
> +	mutex_lock(&bdev->bd_disk->open_mutex);
> +
> +	WARN_ON_ONCE(!bdev->bd_holder);
> +
> +	/* FIXME: remove the following once add_disk() handles errors */
> +	if (WARN_ON(!disk->slave_dir || !bdev->bd_holder_dir))
> +		goto out_unlock;
> +
> +	holder = bd_find_holder_disk(bdev, disk);
> +	if (holder) {
> +		holder->refcnt++;
> +		goto out_unlock;
> +	}
> +
> +	holder = kzalloc(sizeof(*holder), GFP_KERNEL);
> +	if (!holder) {
> +		ret = -ENOMEM;
> +		goto out_unlock;
> +	}
> +
> +	INIT_LIST_HEAD(&holder->list);
> +	holder->disk = disk;
> +	holder->refcnt = 1;
> +
> +	ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
> +	if (ret)
> +		goto out_free;
> +
> +	ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
> +	if (ret)
> +		goto out_del;
> +	/*
> +	 * bdev could be deleted beneath us which would implicitly destroy
> +	 * the holder directory.  Hold on to it.
> +	 */
> +	kobject_get(bdev->bd_holder_dir);
> +
> +	list_add(&holder->list, &bdev->bd_holder_disks);
> +	goto out_unlock;
> +
> +out_del:
> +	del_symlink(disk->slave_dir, bdev_kobj(bdev));
> +out_free:
> +	kfree(holder);
> +out_unlock:
> +	mutex_unlock(&bdev->bd_disk->open_mutex);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(bd_link_disk_holder);
> +
> +/**
> + * bd_unlink_disk_holder - destroy symlinks created by bd_link_disk_holder()
> + * @bdev: the calimed slave bdev
> + * @disk: the holding disk
> + *
> + * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
> + *
> + * CONTEXT:
> + * Might sleep.
> + */
> +void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
> +{
> +	struct bd_holder_disk *holder;
> +
> +	mutex_lock(&bdev->bd_disk->open_mutex);
> +	holder = bd_find_holder_disk(bdev, disk);
> +	if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
> +		del_symlink(disk->slave_dir, bdev_kobj(bdev));
> +		del_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
> +		kobject_put(bdev->bd_holder_dir);
> +		list_del_init(&holder->list);
> +		kfree(holder);
> +	}
> +	mutex_unlock(&bdev->bd_disk->open_mutex);
> +}
> +EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index 0602e82a9516..f821dae101a9 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -15,6 +15,7 @@ if MD
>  
>  config BLK_DEV_MD
>  	tristate "RAID support"
> +	select BLOCK_HOLDER_DEPRECATED if SYSFS
>  	help
>  	  This driver lets you combine several hard disk partitions into one
>  	  logical block device. This can be used to simply append one
> @@ -201,6 +202,7 @@ config BLK_DEV_DM_BUILTIN
>  
>  config BLK_DEV_DM
>  	tristate "Device mapper support"
> +	select BLOCK_HOLDER_DEPRECATED if SYSFS
>  	select BLK_DEV_DM_BUILTIN
>  	depends on DAX || DAX=n
>  	help
> diff --git a/drivers/md/bcache/Kconfig b/drivers/md/bcache/Kconfig
> index d1ca4d059c20..cf3e8096942a 100644
> --- a/drivers/md/bcache/Kconfig
> +++ b/drivers/md/bcache/Kconfig
> @@ -2,6 +2,7 @@
>  
>  config BCACHE
>  	tristate "Block device as cache"
> +	select BLOCK_HOLDER_DEPRECATED if SYSFS
>  	select CRC64
>  	help
>  	Allows a block device to be used as cache for other devices; uses
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 0c424a0cadaa..7825d152634e 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -900,7 +900,7 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
>  	bdev->bd_disk = disk;
>  	bdev->bd_partno = partno;
>  	bdev->bd_inode = inode;
> -#ifdef CONFIG_SYSFS
> +#ifdef CONFIG_BLOCK_HOLDER_DEPRECATED
>  	INIT_LIST_HEAD(&bdev->bd_holder_disks);
>  #endif
>  	bdev->bd_stats = alloc_percpu(struct disk_stats);
> @@ -1092,148 +1092,6 @@ void bd_abort_claiming(struct block_device *bdev, void *holder)
>  }
>  EXPORT_SYMBOL(bd_abort_claiming);
>  
> -#ifdef CONFIG_SYSFS
> -struct bd_holder_disk {
> -	struct list_head	list;
> -	struct gendisk		*disk;
> -	int			refcnt;
> -};
> -
> -static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
> -						  struct gendisk *disk)
> -{
> -	struct bd_holder_disk *holder;
> -
> -	list_for_each_entry(holder, &bdev->bd_holder_disks, list)
> -		if (holder->disk == disk)
> -			return holder;
> -	return NULL;
> -}
> -
> -static int add_symlink(struct kobject *from, struct kobject *to)
> -{
> -	return sysfs_create_link(from, to, kobject_name(to));
> -}
> -
> -static void del_symlink(struct kobject *from, struct kobject *to)
> -{
> -	sysfs_remove_link(from, kobject_name(to));
> -}
> -
> -/**
> - * bd_link_disk_holder - create symlinks between holding disk and slave bdev
> - * @bdev: the claimed slave bdev
> - * @disk: the holding disk
> - *
> - * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
> - *
> - * This functions creates the following sysfs symlinks.
> - *
> - * - from "slaves" directory of the holder @disk to the claimed @bdev
> - * - from "holders" directory of the @bdev to the holder @disk
> - *
> - * For example, if /dev/dm-0 maps to /dev/sda and disk for dm-0 is
> - * passed to bd_link_disk_holder(), then:
> - *
> - *   /sys/block/dm-0/slaves/sda --> /sys/block/sda
> - *   /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
> - *
> - * The caller must have claimed @bdev before calling this function and
> - * ensure that both @bdev and @disk are valid during the creation and
> - * lifetime of these symlinks.
> - *
> - * CONTEXT:
> - * Might sleep.
> - *
> - * RETURNS:
> - * 0 on success, -errno on failure.
> - */
> -int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
> -{
> -	struct bd_holder_disk *holder;
> -	int ret = 0;
> -
> -	mutex_lock(&bdev->bd_disk->open_mutex);
> -
> -	WARN_ON_ONCE(!bdev->bd_holder);
> -
> -	/* FIXME: remove the following once add_disk() handles errors */
> -	if (WARN_ON(!disk->slave_dir || !bdev->bd_holder_dir))
> -		goto out_unlock;
> -
> -	holder = bd_find_holder_disk(bdev, disk);
> -	if (holder) {
> -		holder->refcnt++;
> -		goto out_unlock;
> -	}
> -
> -	holder = kzalloc(sizeof(*holder), GFP_KERNEL);
> -	if (!holder) {
> -		ret = -ENOMEM;
> -		goto out_unlock;
> -	}
> -
> -	INIT_LIST_HEAD(&holder->list);
> -	holder->disk = disk;
> -	holder->refcnt = 1;
> -
> -	ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
> -	if (ret)
> -		goto out_free;
> -
> -	ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
> -	if (ret)
> -		goto out_del;
> -	/*
> -	 * bdev could be deleted beneath us which would implicitly destroy
> -	 * the holder directory.  Hold on to it.
> -	 */
> -	kobject_get(bdev->bd_holder_dir);
> -
> -	list_add(&holder->list, &bdev->bd_holder_disks);
> -	goto out_unlock;
> -
> -out_del:
> -	del_symlink(disk->slave_dir, bdev_kobj(bdev));
> -out_free:
> -	kfree(holder);
> -out_unlock:
> -	mutex_unlock(&bdev->bd_disk->open_mutex);
> -	return ret;
> -}
> -EXPORT_SYMBOL_GPL(bd_link_disk_holder);
> -
> -/**
> - * bd_unlink_disk_holder - destroy symlinks created by bd_link_disk_holder()
> - * @bdev: the calimed slave bdev
> - * @disk: the holding disk
> - *
> - * DON'T USE THIS UNLESS YOU'RE ALREADY USING IT.
> - *
> - * CONTEXT:
> - * Might sleep.
> - */
> -void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
> -{
> -	struct bd_holder_disk *holder;
> -
> -	mutex_lock(&bdev->bd_disk->open_mutex);
> -
> -	holder = bd_find_holder_disk(bdev, disk);
> -
> -	if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
> -		del_symlink(disk->slave_dir, bdev_kobj(bdev));
> -		del_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
> -		kobject_put(bdev->bd_holder_dir);
> -		list_del_init(&holder->list);
> -		kfree(holder);
> -	}
> -
> -	mutex_unlock(&bdev->bd_disk->open_mutex);
> -}
> -EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
> -#endif
> -
>  static void blkdev_flush_mapping(struct block_device *bdev)
>  {
>  	WARN_ON_ONCE(bdev->bd_holders);
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 290f9061b29a..7a4e139d24ef 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -34,7 +34,7 @@ struct block_device {
>  	void *			bd_holder;
>  	int			bd_holders;
>  	bool			bd_write_holder;
> -#ifdef CONFIG_SYSFS
> +#ifdef CONFIG_BLOCK_HOLDER_DEPRECATED
>  	struct list_head	bd_holder_disks;
>  #endif
>  	struct kobject		*bd_holder_dir;
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 13b34177cc85..6831d74f2002 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -316,7 +316,7 @@ void set_capacity(struct gendisk *disk, sector_t size);
>  int blkdev_ioctl(struct block_device *, fmode_t, unsigned, unsigned long);
>  long compat_blkdev_ioctl(struct file *, unsigned, unsigned long);
>  
> -#ifdef CONFIG_SYSFS
> +#ifdef CONFIG_BLOCK_HOLDER_DEPRECATED
>  int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk);
>  void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk);
>  #else
> @@ -329,7 +329,7 @@ static inline void bd_unlink_disk_holder(struct block_device *bdev,
>  					 struct gendisk *disk)
>  {
>  }
> -#endif /* CONFIG_SYSFS */
> +#endif /* CONFIG_BLOCK_HOLDER_DEPRECATED */
>  
>  dev_t part_devt(struct gendisk *disk, u8 partno);
>  dev_t blk_lookup_devt(const char *name, int partno);
> -- 
> 2.30.2
>