struct request documentation

Jens Axboe <> 27/05/02

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).


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