fs/block_dev.c: add bdev_read_page() and bdev_write_page()
A block device driver may choose to provide a rw_page operation. These
will be called when the filesystem is attempting to do page sized I/O to
page cache pages (ie not for direct I/O). This does preclude I/Os that
are larger than page size, so this may only be a performance gain for
some devices.
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Tested-by: Dheeraj Reddy <dheeraj.reddy@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 552a8d1..83fba15 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -363,6 +363,69 @@
}
EXPORT_SYMBOL(blkdev_fsync);
+/**
+ * bdev_read_page() - Start reading a page from a block device
+ * @bdev: The device to read the page from
+ * @sector: The offset on the device to read the page to (need not be aligned)
+ * @page: The page to read
+ *
+ * On entry, the page should be locked. It will be unlocked when the page
+ * has been read. If the block driver implements rw_page synchronously,
+ * that will be true on exit from this function, but it need not be.
+ *
+ * Errors returned by this function are usually "soft", eg out of memory, or
+ * queue full; callers should try a different route to read this page rather
+ * than propagate an error back up the stack.
+ *
+ * Return: negative errno if an error occurs, 0 if submission was successful.
+ */
+int bdev_read_page(struct block_device *bdev, sector_t sector,
+ struct page *page)
+{
+ const struct block_device_operations *ops = bdev->bd_disk->fops;
+ if (!ops->rw_page)
+ return -EOPNOTSUPP;
+ return ops->rw_page(bdev, sector + get_start_sect(bdev), page, READ);
+}
+EXPORT_SYMBOL_GPL(bdev_read_page);
+
+/**
+ * bdev_write_page() - Start writing a page to a block device
+ * @bdev: The device to write the page to
+ * @sector: The offset on the device to write the page to (need not be aligned)
+ * @page: The page to write
+ * @wbc: The writeback_control for the write
+ *
+ * On entry, the page should be locked and not currently under writeback.
+ * On exit, if the write started successfully, the page will be unlocked and
+ * under writeback. If the write failed already (eg the driver failed to
+ * queue the page to the device), the page will still be locked. If the
+ * caller is a ->writepage implementation, it will need to unlock the page.
+ *
+ * Errors returned by this function are usually "soft", eg out of memory, or
+ * queue full; callers should try a different route to write this page rather
+ * than propagate an error back up the stack.
+ *
+ * Return: negative errno if an error occurs, 0 if submission was successful.
+ */
+int bdev_write_page(struct block_device *bdev, sector_t sector,
+ struct page *page, struct writeback_control *wbc)
+{
+ int result;
+ int rw = (wbc->sync_mode == WB_SYNC_ALL) ? WRITE_SYNC : WRITE;
+ const struct block_device_operations *ops = bdev->bd_disk->fops;
+ if (!ops->rw_page)
+ return -EOPNOTSUPP;
+ set_page_writeback(page);
+ result = ops->rw_page(bdev, sector + get_start_sect(bdev), page, rw);
+ if (result)
+ end_page_writeback(page);
+ else
+ unlock_page(page);
+ return result;
+}
+EXPORT_SYMBOL_GPL(bdev_write_page);
+
/*
* pseudo-fs
*/
