From 93e9d8e836cb1a9a58b33eb6643bf061c6119ef2 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Tue, 12 Apr 2016 12:32:46 -0600 Subject: 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 Reviewed-by: Christoph Hellwig --- Documentation/block/queue-sysfs.txt | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'Documentation/block') 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 , February 2009 -- cgit v1.2.3