Re: [PATCH v6 03/10] block: introduce storage element management

[Hannes Reinecke <hare@suse.de>]

On 10/13/26 2:27 PM, Damien Le Moal wrote:
> Recent SCSI (SBC) and ATA (ACS) standards define the storage element
> depopulation feature. This feature is intended for managing hard-disks
> heads, either combined read-write heads or pairs of read and write heads,
> allowing to keep disks with defective heads longer in production by
> allowing "depopulating" (removing) defective heads.
> 
> This feature comes in two different flavors:
>   - A destructive version which removes a head and reformats the disk at a
>     lower capacity point, restoaring a fully functional contiguous LBA
>     address space.
>   - A data preserving version restricted to host-managed zoned disks, which
>     marks the zones served by a removed head as offline or read-only.
> 
> In preparation for using the data-preserving flavor of the depopulation
> feature in file systems natively supporting zoned block devices, introduce
> a set of storage element management operations and functions to define
> generic calls into block device drivers for managing storage elements.
> 
> The set of operations is defined with struct blk_se_ops and includes three
> operations:
>   - report_elements: get information on a device storage elements state
>     reported with the new struct blk_se.
>   - remove_element: depopulate a defective storage element
>   - restore_elements: restore depopulated storage elements
> 
> Each operation is called from the functions
> bdev_report_storage_elements(), bdev_remove_storage_element() and
> bdev_restore_storage_elements().
> 
> Removing a healthy storage element from a device is possible and useful
> for testing. The storage element restoration operation restore_elements
> allows repopulating such healthy element. Repopulating defective storage
> elements is generally not allowed by devices. The remove_element and
> restore_elements operations are executed under the zone revalidation lock
> so that they are serialized iand also serialized against user initiated
> device revalidation, thus allowing to always have a consistent view of the
> device zone conditions.
> 
> The device drivers of zoned block devices can indicate support for the
> storage element depopulation feature by specifying the storage element
> management operations with the se_ops field of struct
> block_device_operations.
> 
> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
> ---
>   block/blk-zoned.c             | 291 +++++++++++++++++++++++++++++++++-
>   block/blk.h                   |   5 +
>   block/genhd.c                 |   4 +
>   include/linux/blkdev.h        |  22 +++
>   include/uapi/linux/blkzoned.h |  62 ++++++++
>   5 files changed, 383 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-zoned.c b/block/blk-zoned.c
> index acec8a7e648e..252d12254692 100644
> --- a/block/blk-zoned.c
> +++ b/block/blk-zoned.c
> @@ -18,6 +18,7 @@
>   #include <linux/mempool.h>
>   #include <linux/kthread.h>
>   #include <linux/freezer.h>
> +#include <linux/delay.h>
>   
>   #include <trace/events/block.h>
>   
> @@ -2721,5 +2722,293 @@ int queue_zone_wplugs_show(void *data, struct seq_file *m)
>   
>   	return 0;
>   }
> -
>   #endif
> +
> +static int disk_se_mgmt_in_progress(struct gendisk *disk,
> +				     struct blk_se *elements,
> +				     bool *in_progress)
> +{
> +	unsigned int i, nr_se = disk->nr_storage_elements;
> +	int ret;
> +
> +	/*
> +	 * Check if we have storage elements being removed or restored.
> +	 */
> +	ret = disk->fops->se_ops->report_elements(disk, elements, &nr_se);
> +	if (ret) {
> +		pr_err("Failed to get storage elements\n");
> +		return ret;
> +	}
> +
> +	for (i = 0; i < nr_se; i++) {
> +		switch (elements[i].status) {
> +		case BLK_SE_STS_REMOVE_IN_PROGRESS:
> +		case BLK_SE_STS_RESTORE_IN_PROGRESS:
> +			*in_progress = true;
> +			return 0;
> +		default:
> +			break;
> +		}
> +	}
> +
> +	*in_progress = false;
> +
> +	return 0;
> +}
> +
> +static int disk_check_remove_error(struct gendisk *disk,
> +				   struct blk_se *elements,
> +				   unsigned int element_id)
> +{
> +	unsigned int i;
> +
> +	for (i = 0; i < disk->nr_storage_elements; i++) {
> +		if (elements[i].id == element_id &&
> +		    elements[i].status == BLK_SE_STS_REMOVE_ERROR)
> +			return -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +static int disk_wait_for_se_mgmt_completion(struct gendisk *disk,
> +					    struct blk_se *elements,
> +					    unsigned int element_id)
> +{
> +	bool in_progress;
> +	int ret;
> +
> +	/*
> +	 * Poll the storage elements heath state to detect the end of a
> +	 * removal or restoration operation. Since we do not know how long the
> +	 * operation may take, we cannot have a timeout on this loop. So check
> +	 * for fatal signals so that the user can terminate this retry loop if
> +	 * the device misbehaves.
> +	 */
> +	while (1) {
> +		ret = disk_se_mgmt_in_progress(disk, elements, &in_progress);
> +		if (ret || !in_progress)
> +			break;
> +
> +		if (fatal_signal_pending(current)) {
> +			ret = -EINTR;
> +			break;
> +		}
> +
> +		/* Not done yet: wait and retry. */
> +		msleep(1000);
> +	}
> +
I always feel a bit uncomfortable having to poll without a dedicated
end time.
Care to add a timeout here to avoid an infinite wait?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich