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============================
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struct request documentation
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============================
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2007-10-15 13:42:52 +04:00
Jens Axboe <jens.axboe@oracle.com> 27/05/02
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.. 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
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3.0
2.0
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Short explanation of request members
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====================================
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Classification flags:
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= ====================
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D driver member
B block layer member
I I/O scheduler member
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= ====================
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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>
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Member Flag Comment
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struct list_head queuelist BI Organization on various internal
queues
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`` void *elevator_private ` ` I I/O scheduler private data
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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
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`` void *special ` ` D Free to be used by driver
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`` char *buffer ` ` D Map of first segment, also see
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section on bouncing SECTION
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`` struct completion *waiting ` ` D Can be used by driver to get signalled
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on request completion
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`` struct bio *bio ` ` DBI First bio in request
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`` struct bio *biotail ` ` DBI Last bio in request
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`` struct request_queue *q ` ` DB Request queue this request belongs to
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`` struct request_list *rl ` ` B Request list this request came from
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