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