Documentation/block/request.txt

   1
   2 struct request documentation
   3
   4 Jens Axboe <jens.axboe@oracle.com> 27/05/02
   5
   6 1.0
   7 Index
   8
   9 2.0 Struct request members classification
  10
  11         2.1 struct request members explanation
  12
  13 3.0
  14
  15
  16 2.0
  17 Short explanation of request members
  18
  19 Classification flags:
  20
  21         D       driver member
  22         B       block layer member
  23         I       I/O scheduler member
  24
  25 Unless an entry contains a D classification, a device driver must not access
  26 this member. Some members may contain D classifications, but should only be
  27 access through certain macros or functions (eg ->flags).
  28
  29 <linux/blkdev.h>
  30
  31 2.1
  32 Member                          Flag    Comment
  33 ------                          ----    -------
  34
  35 struct list_head queuelist      BI      Organization on various internal
  36                                         queues
  37
  38 void *elevator_private          I       I/O scheduler private data
  39
  40 unsigned char cmd[16]           D       Driver can use this for setting up
  41                                         a cdb before execution, see
  42                                         blk_queue_prep_rq
  43
  44 unsigned long flags             DBI     Contains info about data direction,
  45                                         request type, etc.
  46
  47 int rq_status                   D       Request status bits
  48
  49 kdev_t rq_dev                   DBI     Target device
  50
  51 int errors                      DB      Error counts
  52
  53 sector_t sector                 DBI     Target location
  54
  55 unsigned long hard_nr_sectors   B       Used to keep sector sane
  56
  57 unsigned long nr_sectors        DBI     Total number of sectors in request
  58
  59 unsigned long hard_nr_sectors   B       Used to keep nr_sectors sane
  60
  61 unsigned short nr_phys_segments DB      Number of physical scatter gather
  62                                         segments in a request
  63
  64 unsigned short nr_hw_segments   DB      Number of hardware scatter gather
  65                                         segments in a request
  66
  67 unsigned int current_nr_sectors DB      Number of sectors in first segment
  68                                         of request
  69
  70 unsigned int hard_cur_sectors   B       Used to keep current_nr_sectors sane
  71
  72 int tag                         DB      TCQ tag, if assigned
  73
  74 void *special                   D       Free to be used by driver
  75
  76 char *buffer                    D       Map of first segment, also see
  77                                         section on bouncing SECTION
  78
  79 struct completion *waiting      D       Can be used by driver to get signalled
  80                                         on request completion
  81
  82 struct bio *bio                 DBI     First bio in request
  83
  84 struct bio *biotail             DBI     Last bio in request
  85
  86 struct request_queue *q         DB      Request queue this request belongs to
  87
  88 struct request_list *rl         B       Request list this request came from