Re: [PATCH v3 1/4] block: Add concurrent positioning ranges support

Damien Le Moal
2021-07-26T08:30:30Z

On 2021/07/26 16:34, Hannes Reinecke wrote:
> On 7/26/21 3:38 AM, Damien Le Moal wrote:
>> The Concurrent Positioning Ranges VPD page (for SCSI) and Log (for ATA)
>> contain parameters describing the number of sets of contiguous LBAs that
>> can be served independently by a single LUN multi-actuator disk. This
>> patch provides the blk_queue_set_cranges() function allowing a device
>> driver to signal to the block layer that a disk has multiple actuators,
>> each one serving a contiguous range of sectors. To describe the set
>> of sector ranges representing the different actuators of a device, the
>> data type struct blk_cranges is introduced.
>>
>> For a device with multiple actuators, a struct blk_cranges is attached
>> to the device request queue by the blk_queue_set_cranges() function. The
>> function blk_alloc_cranges() is provided for drivers to allocate this
>> structure.
>>
>> The blk_cranges structure contains kobjects (struct kobject) to register
>> with sysfs the set of sector ranges defined by a device. On initial
>> device scan, this registration is done from blk_register_queue() using
>> the block layer internal function blk_register_cranges(). If a driver
>> calls blk_queue_set_cranges() for a registered queue, e.g. when a device
>> is revalidated, blk_queue_set_cranges() will execute
>> blk_register_cranges() to update the queue sysfs attribute files.
>>
>> The sysfs file structure created starts from the cranges sub-directory
>> and contains the start sector and number of sectors served by an
>> actuator, with the information for each actuator grouped in one
>> directory per actuator. E.g. for a dual actuator drive, we have:
>>
>> $ tree /sys/block/sdk/queue/cranges/
>> /sys/block/sdk/queue/cranges/
>> |-- 0
>> | |-- nr_sectors
>> | `-- sector
>> `-- 1
>> |-- nr_sectors
>> `-- sector
>>
>> For a regular single actuator device, the cranges directory does not
>> exist.
>>
>> Device revalidation may lead to changes to this structure and to the
>> attribute values. When manipulated, the queue sysfs_lock and
>> sysfs_dir_lock are held for atomicity, similarly to how the blk-mq and
>> elevator sysfs queue sub-directories are protected.
>>
>> The code related to the management of cranges is added in the new
>> file block/blk-cranges.c.
>>
>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>> ---
>> block/Makefile | 2 +-
>> block/blk-cranges.c | 295 +++++++++++++++++++++++++++++++++++++++++
>> block/blk-sysfs.c | 13 ++
>> block/blk.h | 3 +
>> include/linux/blkdev.h | 29 ++++
>> 5 files changed, 341 insertions(+), 1 deletion(-)
>> create mode 100644 block/blk-cranges.c
>>
>> diff --git a/block/Makefile b/block/Makefile
>> index bfbe4e13ca1e..e477e6ca9ea6 100644
>> --- a/block/Makefile
>> +++ b/block/Makefile
>> @@ -9,7 +9,7 @@ obj-$(CONFIG_BLOCK) := bio.o elevator.o blk-core.o blk-sysfs.o \
>> blk-lib.o blk-mq.o blk-mq-tag.o blk-stat.o \
>> blk-mq-sysfs.o blk-mq-cpumap.o blk-mq-sched.o ioctl.o \
>> genhd.o ioprio.o badblocks.o partitions/ blk-rq-qos.o \
>> - disk-events.o
>> + disk-events.o blk-cranges.o
>>
>> obj-$(CONFIG_BOUNCE) += bounce.o
>> obj-$(CONFIG_BLK_SCSI_REQUEST) += scsi_ioctl.o
>> diff --git a/block/blk-cranges.c b/block/blk-cranges.c
>> new file mode 100644
>> index 000000000000..deaa09e564f7
>> --- /dev/null
>> +++ b/block/blk-cranges.c
>> @@ -0,0 +1,295 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Block device concurrent positioning ranges.
>> + *
>> + * Copyright (C) 2021 Western Digital Corporation or its Affiliates.
>> + */
>> +#include <linux/kernel.h>
>> +#include <linux/blkdev.h>
>> +#include <linux/slab.h>
>> +#include <linux/init.h>
>> +
>> +#include "blk.h"
>> +
>> +static ssize_t blk_crange_sector_show(struct blk_crange *cr, char *page)
>> +{
>> + return sprintf(page, "%llu\n", cr->sector);
>> +}
>> +
>> +static ssize_t blk_crange_nr_sectors_show(struct blk_crange *cr, char *page)
>> +{
>> + return sprintf(page, "%llu\n", cr->nr_sectors);
>> +}
>> +
>> +struct blk_crange_sysfs_entry {
>> + struct attribute attr;
>> + ssize_t (*show)(struct blk_crange *cr, char *page);
>> +};
>> +
>> +static struct blk_crange_sysfs_entry blk_crange_sector_entry = {
>> + .attr = { .name = "sector", .mode = 0444 },
>> + .show = blk_crange_sector_show,
>> +};
>> +
>> +static struct blk_crange_sysfs_entry blk_crange_nr_sectors_entry = {
>> + .attr = { .name = "nr_sectors", .mode = 0444 },
>> + .show = blk_crange_nr_sectors_show,
>> +};
>> +
>> +static struct attribute *blk_crange_attrs[] = {
>> + &blk_crange_sector_entry.attr,
>> + &blk_crange_nr_sectors_entry.attr,
>> + NULL,
>> +};
>> +ATTRIBUTE_GROUPS(blk_crange);
>> +
>> +static ssize_t blk_crange_sysfs_show(struct kobject *kobj,
>> + struct attribute *attr, char *page)
>> +{
>> + struct blk_crange_sysfs_entry *entry;
>> + struct blk_crange *cr;
>> + struct request_queue *q;
>> + ssize_t ret;
>> +
>> + entry = container_of(attr, struct blk_crange_sysfs_entry, attr);
>> + cr = container_of(kobj, struct blk_crange, kobj);
>> + q = cr->queue;
>> +
>> + mutex_lock(&q->sysfs_lock);
>> + ret = entry->show(cr, page);
>> + mutex_unlock(&q->sysfs_lock);
>> +
>> + return ret;
>> +}
>> +
>> +static const struct sysfs_ops blk_crange_sysfs_ops = {
>> + .show = blk_crange_sysfs_show,
>> +};
>> +
>> +/*
>> + * Dummy release function to make kobj happy.
>> + */
>> +static void blk_cranges_sysfs_nop_release(struct kobject *kobj)
>> +{
>> +}
>> +
>> +static struct kobj_type blk_crange_ktype = {
>> + .sysfs_ops = &blk_crange_sysfs_ops,
>> + .default_groups = blk_crange_groups,
>> + .release = blk_cranges_sysfs_nop_release,
>> +};
>> +
>> +static struct kobj_type blk_cranges_ktype = {
>> + .release = blk_cranges_sysfs_nop_release,
>> +};
>> +
>> +/**
>> + * blk_register_cranges - register with sysfs a set of concurrent ranges
>> + * @disk: Target disk
>> + * @new_cranges: New set of concurrent ranges
>> + *
>> + * Register with sysfs a set of concurrent ranges for @disk. If @new_cranges
>> + * is not NULL, this set of concurrent ranges is registered and the
>> + * old set specified by q->cranges is unregistered. Otherwise, q->cranges
>> + * is registered if it is not already.
>> + */
>> +int blk_register_cranges(struct gendisk *disk, struct blk_cranges *new_cranges)
>> +{
>> + struct request_queue *q = disk->queue;
>> + struct blk_cranges *cranges;
>> + int i, ret;
>> +
>> + lockdep_assert_held(&q->sysfs_dir_lock);
>> + lockdep_assert_held(&q->sysfs_lock);
>> +
>> + /* If a new range set is specified, unregister the old one */
>> + if (new_cranges) {
>> + if (q->cranges)
>> + blk_unregister_cranges(disk);
>> + q->cranges = new_cranges;
>> + }
>> +
>> + cranges = q->cranges;
>> + if (!cranges)
>> + return 0;
>> +
>> + /*
>> + * At this point, q->cranges is the new set of sector ranges that needs
>> + * to be registered with sysfs.
>> + */
>> + WARN_ON(cranges->sysfs_registered);
>> + ret = kobject_init_and_add(&cranges->kobj, &blk_cranges_ktype,
>> + &q->kobj, "%s", "cranges");
>> + if (ret)
>> + goto free;
>> +
>> + for (i = 0; i < cranges->nr_ranges; i++) {
>> + cranges->ranges[i].queue = q;
>> + ret = kobject_init_and_add(&cranges->ranges[i].kobj,
>> + &blk_crange_ktype, &cranges->kobj,
>> + "%d", i);
>> + if (ret)
>> + goto delete_obj;
>> + }
>> +
>> + cranges->sysfs_registered = true;
>> +
>> + return 0;
>> +
>> +delete_obj:
>> + while (--i >= 0)
>> + kobject_del(&cranges->ranges[i].kobj);
>> + kobject_del(&cranges->kobj);
>> +free:
>> + kfree(cranges);
>> + q->cranges = NULL;
>> + return ret;
>> +}
>> +
>> +void blk_unregister_cranges(struct gendisk *disk)
>> +{
>> + struct request_queue *q = disk->queue;
>> + struct blk_cranges *cranges = q->cranges;
>> + int i;
>> +
>> + lockdep_assert_held(&q->sysfs_dir_lock);
>> + lockdep_assert_held(&q->sysfs_lock);
>> +
>> + if (!cranges)
>> + return;
>> +
>> + if (cranges->sysfs_registered) {
>> + for (i = 0; i < cranges->nr_ranges; i++)
>> + kobject_del(&cranges->ranges[i].kobj);
>> + kobject_del(&cranges->kobj);
>> + }
>> +
>> + kfree(cranges);
>> + q->cranges = NULL;
>> +}
>> +
>> +static bool blk_check_ranges(struct gendisk *disk, struct blk_cranges *cr)
>> +{
>> + sector_t capacity = get_capacity(disk);
>> + sector_t min_sector = (sector_t)-1;
>> + sector_t max_sector = 0;
>> + int i;
>> +
>> + /*
>> + * Sector ranges may overlap but should overall contain all sectors
>> + * within the disk capacity.
>> + */
>> + for (i = 0; i < cr->nr_ranges; i++) {
>> + min_sector = min(min_sector, cr->ranges[i].sector);
>> + max_sector = max(max_sector, cr->ranges[i].sector +
>> + cr->ranges[i].nr_sectors);
>> + }
>> +
>> + if (min_sector != 0 || max_sector < capacity) {
>> + pr_warn("Invalid concurrent ranges: missing sectors\n");
>> + return false;
>> + }
>> +
>> + if (max_sector > capacity) {
>> + pr_warn("Invalid concurrent ranges: beyond capacity\n");
>> + return false;
>> + }
>> +
>> + return true;
>> +}
>> +
>> +static bool blk_cranges_changed(struct gendisk *disk, struct blk_cranges *new)
>> +{
>> + struct blk_cranges *old = disk->queue->cranges;
>> + int i;
>> +
>> + if (!old)
>> + return true;
>> +
>> + if (old->nr_ranges != new->nr_ranges)
>> + return true;
>> +
>> + for (i = 0; i < old->nr_ranges; i++) {
>> + if (new->ranges[i].sector != old->ranges[i].sector ||
>> + new->ranges[i].nr_sectors != old->ranges[i].nr_sectors)
>> + return true;
>> + }
>> +
>> + return false;
>> +}
>> +
>> +/**
>> + * blk_alloc_cranges - Allocate a concurrent positioning range structure
>> + * @disk: target disk
>> + * @nr_ranges: Number of concurrent ranges
>> + *
>> + * Allocate a struct blk_cranges structure with @nr_ranges range descriptors.
>> + */
>> +struct blk_cranges *blk_alloc_cranges(struct gendisk *disk, int nr_ranges)
>> +{
>> + struct blk_cranges *cr;
>> +
>> + cr = kzalloc_node(struct_size(cr, ranges, nr_ranges), GFP_KERNEL,
>> + disk->queue->node);
>> + if (cr)
>> + cr->nr_ranges = nr_ranges;
>> + return cr;
>> +}
>> +EXPORT_SYMBOL_GPL(blk_alloc_cranges);
>> +
>> +/**
>> + * blk_queue_set_cranges - Set a disk concurrent positioning ranges
>> + * @disk: target disk
>> + * @cr: concurrent ranges structure
>> + *
>> + * Set the concurrant positioning ranges information of the request queue
>> + * of @disk to @cr. If @cr is NULL and the concurrent ranges structure
>> + * already set, if any, is cleared. If there are no differences between
>> + * @cr and the concurrent ranges structure already set, @cr is freed.
>> + */
>> +void blk_queue_set_cranges(struct gendisk *disk, struct blk_cranges *cr)
>> +{
>> + struct request_queue *q = disk->queue;
>> +
>> + if (WARN_ON_ONCE(cr && !cr->nr_ranges)) {
>> + kfree(cr);
>> + cr = NULL;
>> + }
>> +
>> + mutex_lock(&q->sysfs_dir_lock);
>> + mutex_lock(&q->sysfs_lock);
>> +
>> + if (cr) {
>> + if (!blk_check_ranges(disk, cr)) {
>> + kfree(cr);
>> + cr = NULL;
>> + goto reg;
>> + }
>> +
>> + if (!blk_cranges_changed(disk, cr)) {
>> + kfree(cr);
>> + goto unlock;
>> + }
>> + }
>> +
>> + /*
>> + * This may be called for a registered queue. E.g. during a device
>> + * revalidation. If that is the case, we need to unregister the old
>> + * set of concurrent ranges and register the new set. If the queue
>> + * is not registered, the device request queue registration will
>> + * register the ranges, so only swap in the new set and free the
>> + * old one.
>> + */
>> +reg:
>> + if (blk_queue_registered(q)) {
>> + blk_register_cranges(disk, cr);
>> + } else {
>> + swap(q->cranges, cr);
>> + kfree(cr);
>> + }
>> +
>> +unlock:
>> + mutex_unlock(&q->sysfs_lock);
>> + mutex_unlock(&q->sysfs_dir_lock);
>> +}
>> +EXPORT_SYMBOL_GPL(blk_queue_set_cranges);
>> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
>> index 370d83c18057..aeac98ecc5a0 100644
>> --- a/block/blk-sysfs.c
>> +++ b/block/blk-sysfs.c
>> @@ -899,9 +899,21 @@ int blk_register_queue(struct gendisk *disk)
>> }
>>
>> mutex_lock(&q->sysfs_lock);
>> +
>> + ret = blk_register_cranges(disk, NULL);
>> + if (ret) {
>> + mutex_unlock(&q->sysfs_lock);
>> + mutex_unlock(&q->sysfs_dir_lock);
>> + kobject_del(&q->kobj);
>> + blk_trace_remove_sysfs(dev);
>> + kobject_put(&dev->kobj);
>> + return ret;
>> + }
>> +
>> if (q->elevator) {
>> ret = elv_register_queue(q, false);
>> if (ret) {
>> + blk_unregister_cranges(disk);
>> mutex_unlock(&q->sysfs_lock);
>> mutex_unlock(&q->sysfs_dir_lock);
>> kobject_del(&q->kobj);
>> @@ -985,6 +997,7 @@ void blk_unregister_queue(struct gendisk *disk)
>> mutex_lock(&q->sysfs_lock);
>> if (q->elevator)
>> elv_unregister_queue(q);
>> + blk_unregister_cranges(disk);
>> mutex_unlock(&q->sysfs_lock);
>> mutex_unlock(&q->sysfs_dir_lock);
>>
>> diff --git a/block/blk.h b/block/blk.h
>> index 4b885c0f6708..650c0d87987c 100644
>> --- a/block/blk.h
>> +++ b/block/blk.h
>> @@ -368,4 +368,7 @@ extern struct device_attribute dev_attr_events;
>> extern struct device_attribute dev_attr_events_async;
>> extern struct device_attribute dev_attr_events_poll_msecs;
>>
>> +int blk_register_cranges(struct gendisk *disk, struct blk_cranges *new_cranges);
>> +void blk_unregister_cranges(struct gendisk *disk);
>> +
>> #endif /* BLK_INTERNAL_H */
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index d3afea47ade6..d10352674d20 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -378,6 +378,29 @@ static inline int blkdev_zone_mgmt_ioctl(struct block_device *bdev,
>>
>> #endif /* CONFIG_BLK_DEV_ZONED */
>>
>> +/*
>> + * Concurrent sector ranges: struct blk_crange describes range of
>> + * contiguous sectors that can be served by independent resources on the
>> + * device. The set of ranges defined in struct blk_cranges must overall
>> + * include all sectors within the device capacity.
>> + * For a device with multiple ranges, e.g. a single LUN multi-actuator HDD,
>> + * requests targeting sectors in different ranges can be executed in parallel.
>> + * A request can straddle a range boundary.
>> + */
>> +struct blk_crange {
>> + struct kobject kobj;
>> + struct request_queue *queue;
>> + sector_t sector;
>> + sector_t nr_sectors;
>> +};
>> +
>> +struct blk_cranges {
>> + struct kobject kobj;
>> + bool sysfs_registered;
>> + unsigned int nr_ranges;
>> + struct blk_crange ranges[];
>> +};
>> +
>> struct request_queue {
>> struct request *last_merge;
>> struct elevator_queue *elevator;
>> @@ -570,6 +593,9 @@ struct request_queue {
>>
>> #define BLK_MAX_WRITE_HINTS 5
>> u64 write_hints[BLK_MAX_WRITE_HINTS];
>> +
>> + /* Concurrent sector ranges */
>> + struct blk_cranges *cranges;
>> };
>>
>> /* Keep blk_queue_flag_name[] in sync with the definitions below */
>> @@ -1163,6 +1189,9 @@ extern void blk_queue_required_elevator_features(struct request_queue *q,
>> extern bool blk_queue_can_use_dma_map_merging(struct request_queue *q,
>> struct device *dev);
>>
>> +struct blk_cranges *blk_alloc_cranges(struct gendisk *disk, int nr_ranges);
>> +void blk_queue_set_cranges(struct gendisk *disk, struct blk_cranges *cr);
>> +
>> /*
>> * Number of physical segments as sent to the device.
>> *
>>
> In principle it looks good, but what would be the appropriate action
> when invalid ranges are being detected during revalidation?
> The current code will leave the original ones intact, but I guess that's
> questionable as the current settings are most likely invalid.

Nope. In that case, the old ranges are removed. In blk_queue_set_cranges(),
there is:

+ if (!blk_check_ranges(disk, cr)) {
+ kfree(cr);
+ cr = NULL;
+ goto reg;
+ }

So for incorrect ranges, we will register "NULL", so no ranges. The old ranges
are gone.

> I would vote for de-register the old ones and implement an error state
> (using an error pointer?); that would signal that there _are_ ranges,
> but we couldn't parse them properly.
> Hmm?

With the current code, the information "there are ranges" will be completely
gone if the ranges are bad... dmesg will have a message about it, but that's it.

>
> Cheers,
>
> Hannes
>

--
Damien Le Moal
Western Digital Research