diff options
Diffstat (limited to 'Documentation/block')
| -rw-r--r-- | Documentation/block/queue-sysfs.txt | 9 | ||||
| -rw-r--r-- | Documentation/block/writeback_cache_control.txt | 4 |
2 files changed, 11 insertions, 2 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 diff --git a/Documentation/block/writeback_cache_control.txt b/Documentation/block/writeback_cache_control.txt index 83407d36630a..59e0516cbf6b 100644 --- a/Documentation/block/writeback_cache_control.txt +++ b/Documentation/block/writeback_cache_control.txt @@ -71,7 +71,7 @@ requests that have a payload. For devices with volatile write caches the driver needs to tell the block layer that it supports flushing caches by doing: - blk_queue_flush(sdkp->disk->queue, REQ_FLUSH); + blk_queue_write_cache(sdkp->disk->queue, true, false); and handle empty REQ_FLUSH requests in its prep_fn/request_fn. Note that REQ_FLUSH requests with a payload are automatically turned into a sequence @@ -79,7 +79,7 @@ of an empty REQ_FLUSH request followed by the actual write by the block layer. For devices that also support the FUA bit the block layer needs to be told to pass through the REQ_FUA bit using: - blk_queue_flush(sdkp->disk->queue, REQ_FLUSH | REQ_FUA); + blk_queue_write_cache(sdkp->disk->queue, true, true); and the driver must handle write requests that have the REQ_FUA bit set in prep_fn/request_fn. If the FUA bit is not natively supported the block |