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struct request documentation
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Jens Axboe <jens.axboe@oracle.com> 27/05/02
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1.0
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Index
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2.0 Struct request members classification
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2.1 struct request members explanation
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3.0
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2.0
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Short explanation of request members
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Classification flags:
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D driver member
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B block layer member
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I I/O scheduler member
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Unless an entry contains a D classification, a device driver must not access
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this member. Some members may contain D classifications, but should only be
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access through certain macros or functions (eg ->flags).
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<linux/blkdev.h>
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2.1
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Member Flag Comment
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------ ---- -------
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struct list_head queuelist BI Organization on various internal
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queues
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void *elevator_private I I/O scheduler private data
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unsigned char cmd[16] D Driver can use this for setting up
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a cdb before execution, see
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blk_queue_prep_rq
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unsigned long flags DBI Contains info about data direction,
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request type, etc.
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int rq_status D Request status bits
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kdev_t rq_dev DBI Target device
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int errors DB Error counts
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sector_t sector DBI Target location
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unsigned long hard_nr_sectors B Used to keep sector sane
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unsigned long nr_sectors DBI Total number of sectors in request
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unsigned long hard_nr_sectors B Used to keep nr_sectors sane
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unsigned short nr_phys_segments DB Number of physical scatter gather
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segments in a request
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unsigned short nr_hw_segments DB Number of hardware scatter gather
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segments in a request
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unsigned int current_nr_sectors DB Number of sectors in first segment
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of request
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unsigned int hard_cur_sectors B Used to keep current_nr_sectors sane
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int tag DB TCQ tag, if assigned
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void *special D Free to be used by driver
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char *buffer D Map of first segment, also see
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section on bouncing SECTION
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struct completion *waiting D Can be used by driver to get signalled
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on request completion
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struct bio *bio DBI First bio in request
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struct bio *biotail DBI Last bio in request
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struct request_queue *q DB Request queue this request belongs to
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struct request_list *rl B Request list this request came from
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