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Add support for storage element depopulation - #1394
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Introduce the helper function disk_zone_is_offline() for testing if a zone of a gendisk has the offline condition. The zone to test is identified using a sector number that must belong to the target zone to check. Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Split out most of the code of blk_revalidate_disk_zones() into the internal function disk_revalidate_zones(). This will allow calling this new helper together with other code under the zone revalidation mutex. No functional change. Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
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>
Define the new ioctl commands BLKGETNRSTORELEMS, BLKREPORTSTORELEMS, BLKREMOVESTORELEM, and BLKRESTORESTORELEMS to provide users accessing zoned block devices directly with an interface to the storage elements management operations of the block layer. The ioctls BLKGETNRSTORELEMS and BLKREPORTSTORELEMS are defined to respectively get the number of storage elements of a zoned device and to get an array of struct blk_storage_element describing the current state of the device storage elements. The ioctl BLKREMOVESTORELEM can be used to remove (depopulate) a storage element that has a degraded status (i.e. BLK_SE_STS_DEGRADED). Finally, the BLKRESTORESTORELEMS ioctl interfaces with bdev_restore_storage_elements() to restore the depopulated storage elements of a zoned device. Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Emulate the storage element depopulation feature of SMR disks in the zloop driver. This emulation is controlled using the new stor_elements option. This option can take several values: - ZLOOP_STOR_ELEMENTS_NONE (0): no emulation (default) - ZLOOP_STOR_ELEMENTS_RDWR (1): emulate all access storage elements (e.g. read+write heads) - ZLOOP_STOR_ELEMENTS_PAIRS (2): emulate fractional access storage elements (e.g. pairs of read and write heads) If enabled with the value 1 or 2, the number of storage elements, or of pairs of fractional access storage elements, is automatically calculated based on the number of zones of the device so that we have at least 2 and at most 32 storage elements (or 2 pairs of fractional access storage elements). The mapping of zones to storage elements is defined simply as the modulo of a zone number and a storage element ID. E.g, removing a storage element from a set of 4 storage elements will offline 1 zone every 4 zones. The storage element management operations are specified with the zloop_se_ops (struct blk_storage_elements_ops). Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Allow users to mark storage elements of a zloop device as degraded using the new "degrade_element" control command. The element to degrade is indicated using the element_id option. Example: echo "degrade_element id=0,element_id=2" > /dev/zloop-control If the element ID identifies an all access storage element, read and write operations targeting a zone served by the degraded lement are failed. For a partial access storage element, read or write operations are failed depending on the storage element type. This check for an element status is done without taking the storage elements mutex lock, so in order to avoid memory access ordering issues, storage element status access is changed to use READ_ONCE() and WRITE_ONCE() Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Issuing read commands to offline zones of a ZBC disk will result in failures. So do not issue such command and fail then early in sd_setup_read_write_cmnd(). This change also checks write commands, which is fine but should actually never happen as the block layer zone write plugging code already fails write BIOs to offline zones early in the submission path. Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
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…ulation sd_zbc_revalidate_zones() skips revalidating the zones of a ZBC device if the zone size and total number of zones of the disk has not changed. This is to avoid a call to the rather slow blk_revalidate_disk_zones(). However, for ZBC devices that support data preserving head depopulation (REMOVE ELEMENT AND MODIFY ZONES command), a disk capacity and number of zones does not change after a head is depopulated but the condition of zones changes as the zones served by the head that was depopulated become either read-only or offline. In this case, not calling blk_revalidate_disk_zones() prevents the block layer from taking appropriate actions on the zone write plugs of the disk for the zones that became read-only or offline. Avoid any issue with the block layer view of the zone conditions by not skipping the call to blk_revalidate_disk_zones() for disks that support the REMOVE ELEMENT AND MODIFY ZONES command. This check is done from sd_zbc_read_zones() using the helper function sd_zbc_check_modify_zones(). The new scsi disk flag modify_zones_supported is defined to remember the result of this check. Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Define the storage element management operations using struct blk_storage_elements_ops. These operations are valid only on SMR disks supporting the storage element depopulation feature. Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
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Pull request for series with
subject: Add support for storage element depopulation
version: 1
url: https://patchwork.kernel.org/series/1179504/