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Diffstat (limited to 'Documentation/block/biodoc.txt')
| -rw-r--r-- | Documentation/block/biodoc.txt | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt index 8df5e8e..2101e71 100644 --- a/Documentation/block/biodoc.txt +++ b/Documentation/block/biodoc.txt @@ -447,14 +447,13 @@ struct bio_vec { * main unit of I/O for the block layer and lower layers (ie drivers) */ struct bio { - sector_t bi_sector; struct bio *bi_next; /* request queue link */ struct block_device *bi_bdev; /* target device */ unsigned long bi_flags; /* status, command, etc */ unsigned long bi_rw; /* low bits: r/w, high: priority */ unsigned int bi_vcnt; /* how may bio_vec's */ - unsigned int bi_idx; /* current index into bio_vec array */ + struct bvec_iter bi_iter; /* current index into bio_vec array */ unsigned int bi_size; /* total size in bytes */ unsigned short bi_phys_segments; /* segments after physaddr coalesce*/ @@ -480,7 +479,7 @@ With this multipage bio design: - Code that traverses the req list can find all the segments of a bio by using rq_for_each_segment. This handles the fact that a request has multiple bios, each of which can have multiple segments. -- Drivers which can't process a large bio in one shot can use the bi_idx +- Drivers which can't process a large bio in one shot can use the bi_iter field to keep track of the next bio_vec entry to process. (e.g a 1MB bio_vec needs to be handled in max 128kB chunks for IDE) [TBD: Should preferably also have a bi_voffset and bi_vlen to avoid modifying @@ -589,7 +588,7 @@ driver should not modify these values. The block layer sets up the nr_sectors and current_nr_sectors fields (based on the corresponding hard_xxx values and the number of bytes transferred) and updates it on every transfer that invokes end_that_request_first. It does the same for the -buffer, bio, bio->bi_idx fields too. +buffer, bio, bio->bi_iter fields too. The buffer field is just a virtual address mapping of the current segment of the i/o buffer in cases where the buffer resides in low-memory. For high |
