Kernel-2.6.32-573.12.1.el6_request

struct request documentation

Jens Axboe jens.axboe@oracle.com 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