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authorJens Axboe <axboe@fb.com>2016-04-12 12:32:46 -0600
committerJens Axboe <axboe@fb.com>2016-04-12 15:46:27 -0600
commit93e9d8e836cb1a9a58b33eb6643bf061c6119ef2 (patch)
tree17a50abdadaa58686983510230932323bf5d123c /Documentation/block
parente0489487ec9cd79ee1fa0dc5d3789c08b0e51a2c (diff)
block: add ability to flag write back caching on a device
Add an internal helper and flag for setting whether a queue has write back caching, or write through (or none). Add a sysfs file to show this as well, and make it changeable from user space. This will replace the (awkward) blk_queue_flush() interface that drivers currently use to inform the block layer of write cache state and capabilities. Signed-off-by: Jens Axboe <axboe@fb.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
Diffstat (limited to 'Documentation/block')
-rw-r--r--Documentation/block/queue-sysfs.txt9
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt
index e5d914845be6..dce25d848d92 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -141,6 +141,15 @@ control of this block device to that new IO scheduler. Note that writing
an IO scheduler name to this file will attempt to load that IO scheduler
module, if it isn't already present in the system.
+write_cache (RW)
+----------------
+When read, this file will display whether the device has write back
+caching enabled or not. It will return "write back" for the former
+case, and "write through" for the latter. Writing to this file can
+change the kernels view of the device, but it doesn't alter the
+device state. This means that it might not be safe to toggle the
+setting from "write back" to "write through", since that will also
+eliminate cache flushes issued by the kernel.
Jens Axboe <jens.axboe@oracle.com>, February 2009