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Components relying only on the request_queue structure for accessing block devices (e.g. I/O schedulers) have a limited knowledged of the device characteristics. In particular, the device capacity cannot be easily discovered, which for a zoned block device also result in the inability to easily know the number of zones of the device (the zone size is indicated by the chunk_sectors field of the queue limits). Introduce the nr_zones field to the request_queue structure to simplify access to this information. Also, add the bitmap seq_zone_bitmap which indicates which zones of the device are sequential zones (write preferred or write required) and the bitmap seq_zones_wlock which indicates if a zone is write locked, that is, if a write request targeting a zone was dispatched to the device. These fields are initialized by the low level block device driver (sd.c for ZBC/ZAC disks). They are not initialized by stacking drivers (device mappers) handling zoned block devices (e.g. dm-linear). Using this, I/O schedulers can introduce zone write locking to control request dispatching to a zoned block device and avoid write request reordering by limiting to at most a single write request per zone outside of the scheduler at any time. Based on previous patches from Damien Le Moal. Signed-off-by: Christoph Hellwig <hch@lst.de> [Damien] * Fixed comments and identation in blkdev.h * Changed helper functions * Fixed this commit message Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.