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