Remove mentioning of block barriers since they were removed.
Signed-off-by: Leonid V. Fedorenchik <leoni...@gmail.com
Documentation/block/biodoc.txt | 36 +++++++++---------------------------
1 file changed, 9 insertions(+), 27 deletions(-)
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index 5aabc08..fd12c0d 100644
@@ -48,8 +48,7 @@ Description of Contents:
- Highmem I/O support
- I/O scheduler modularization
1.2 Tuning based on high level requirements/capabilities
- 1.2.1 I/O Barriers
- 1.2.2 Request Priority/Latency
+ 1.2.1 Request Priority/Latency
1.3 Direct access/bypass to lower layers for diagnostics and special
1.3.1 Pre-built commands
@@ -255,29 +254,12 @@ some control over i/o ordering.
What kind of support exists at the generic block layer for this ?
The flags and rw fields in the bio structure can be used for some tuning
-from above e.g indicating that an i/o is just a readahead request, or for
-marking barrier requests (discussed next), or priority settings (currently
-unused). As far as user applications are concerned they would need an
-additional mechanism either via open flags or ioctls, or some other upper
-level mechanism to communicate such settings to block.
-1.2.1 I/O Barriers
-There is a way to enforce strict ordering for i/os through barriers.
-All requests before a barrier point must be serviced before the barrier
-request and any other requests arriving after the barrier will not be
-serviced until after the barrier has completed. This is useful for higher
-level control on write ordering, e.g flushing a log of committed updates
-to disk before the corresponding updates themselves.
-A flag in the bio structure, BIO_BARRIER is used to identify a barrier i/o.
-The generic i/o scheduler would make sure that it places the barrier request and
-all other requests coming after it after all the previous requests in the
-queue. Barriers may be implemented in different ways depending on the
-driver. For more details regarding I/O barriers, please read barrier.txt
-in this directory.
-1.2.2 Request Priority/Latency
+from above e.g indicating that an i/o is just a readahead request, or priority
+settings (currently unused). As far as user applications are concerned they
+would need an additional mechanism either via open flags or ioctls, or some
+other upper level mechanism to communicate such settings to block.
+1.2.1 Request Priority/Latency
Arjan's proposed request priority scheme allows higher levels some broad
@@ -906,8 +888,8 @@ queue and specific I/O schedulers. Unless stated otherwise, elevator is used
to refer to both parts and I/O scheduler to specific I/O schedulers.
Block layer implements generic dispatch queue in block/*.c.
-The generic dispatch queue is responsible for properly ordering barrier
-requests, requeueing, handling non-fs requests and all other subtleties.
+The generic dispatch queue is responsible for requeueing, handling non-fs
+requests and all other subtleties.
Specific I/O schedulers are responsible for ordering normal filesystem
requests. They can also choose to delay certain requests to improve
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