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struct request documentation
Jens Axboe <> 27/05/02
2.0 Struct request members classification
2.1 struct request members explanation
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
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
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