1 files changed, 88 insertions, 0 deletions

diff --git a/Documentation/block/request.txt b/Documentation/block/request.txt
new file mode 100644
index 000000000000..75924e2a6975
--- /dev/null
+++ b/Documentation/block/request.txt
@@ -0,0 +1,88 @@
+
+struct request documentation
+
+Jens Axboe <axboe@suse.de> 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
+
+request_queue_t *q              DB      Request queue this request belongs to
+
+struct request_list *rl         B       Request list this request came from