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1
2struct request documentation
3
4Jens Axboe <jens.axboe@oracle.com> 27/05/02
5
61.0
7Index
8
92.0 Struct request members classification
10
11	2.1 struct request members explanation
12
133.0
14
15
162.0
17Short explanation of request members
18
19Classification flags:
20
21	D	driver member
22	B	block layer member
23	I	I/O scheduler member
24
25Unless an entry contains a D classification, a device driver must not access
26this member. Some members may contain D classifications, but should only be
27access through certain macros or functions (eg ->flags).
28
29<linux/blkdev.h>
30
312.1
32Member				Flag	Comment
33------				----	-------
34
35struct list_head queuelist	BI	Organization on various internal
36					queues
37
38void *elevator_private		I	I/O scheduler private data
39
40unsigned char cmd[16]		D	Driver can use this for setting up
41					a cdb before execution, see
42					blk_queue_prep_rq
43
44unsigned long flags		DBI	Contains info about data direction,
45					request type, etc.
46
47int rq_status			D	Request status bits
48
49kdev_t rq_dev			DBI	Target device
50
51int errors			DB	Error counts
52
53sector_t sector			DBI	Target location
54
55unsigned long hard_nr_sectors	B	Used to keep sector sane
56
57unsigned long nr_sectors	DBI	Total number of sectors in request
58
59unsigned long hard_nr_sectors	B	Used to keep nr_sectors sane
60
61unsigned short nr_phys_segments	DB	Number of physical scatter gather
62					segments in a request
63
64unsigned short nr_hw_segments	DB	Number of hardware scatter gather
65					segments in a request
66
67unsigned int current_nr_sectors	DB	Number of sectors in first segment
68					of request
69
70unsigned int hard_cur_sectors	B	Used to keep current_nr_sectors sane
71
72int tag				DB	TCQ tag, if assigned
73
74void *special			D	Free to be used by driver
75
76char *buffer			D	Map of first segment, also see
77					section on bouncing SECTION
78
79struct completion *waiting	D	Can be used by driver to get signalled
80					on request completion
81
82struct bio *bio			DBI	First bio in request
83
84struct bio *biotail		DBI	Last bio in request
85
86struct request_queue *q		DB	Request queue this request belongs to
87
88struct request_list *rl		B	Request list this request came from
89