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============================
struct request documentation
============================
Jens Axboe <jens.axboe@oracle.com> 27/05/02
.. FIXME:
No idea about what does mean - seems just some noise, so comment it
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>
=============================== ======= =======================================
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
=============================== ======= =======================================
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