diff options
author | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 15:20:36 -0700 |
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committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 15:20:36 -0700 |
commit | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch) | |
tree | 0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/block/request.txt |
Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Diffstat (limited to 'Documentation/block/request.txt')
-rw-r--r-- | Documentation/block/request.txt | 88 |
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 |