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Documentation/block/request.txt 2.03 KB
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1da177e4c   Linus Torvalds   Linux-2.6.12-rc2 
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  struct request documentation
26bbb29a2   Rob Landley   Update Jens Axboe... 
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  Jens Axboe <jens.axboe@oracle.com> 27/05/02
1da177e4c   Linus Torvalds   Linux-2.6.12-rc2 
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  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
165125e1e   Jens Axboe   [BLOCK] Get rid o... 
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  struct request_queue *q		DB	Request queue this request belongs to
1da177e4c   Linus Torvalds   Linux-2.6.12-rc2 
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  struct request_list *rl		B	Request list this request came from