[PATCH] add AOP_TRUNCATED_PAGE, prepend AOP_ to WRITEPAGE_ACTIVATE
readpage(), prepare_write(), and commit_write() callers are updated to
understand the special return code AOP_TRUNCATED_PAGE in the style of
writepage() and WRITEPAGE_ACTIVATE. AOP_TRUNCATED_PAGE tells the caller that
the callee has unlocked the page and that the operation should be tried again
with a new page. OCFS2 uses this to detect and work around a lock inversion in
its aop methods. There should be no change in behaviour for methods that don't
return AOP_TRUNCATED_PAGE.
WRITEPAGE_ACTIVATE is also prepended with AOP_ for consistency and they are
made enums so that kerneldoc can be used to document their semantics.
Signed-off-by: Zach Brown <zach.brown@oracle.com>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cc35b6a..ed9a41a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -302,6 +302,37 @@
*/
#include <linux/quota.h>
+/**
+ * enum positive_aop_returns - aop return codes with specific semantics
+ *
+ * @AOP_WRITEPAGE_ACTIVATE: Informs the caller that page writeback has
+ * completed, that the page is still locked, and
+ * should be considered active. The VM uses this hint
+ * to return the page to the active list -- it won't
+ * be a candidate for writeback again in the near
+ * future. Other callers must be careful to unlock
+ * the page if they get this return. Returned by
+ * writepage();
+ *
+ * @AOP_TRUNCATED_PAGE: The AOP method that was handed a locked page has
+ * unlocked it and the page might have been truncated.
+ * The caller should back up to acquiring a new page and
+ * trying again. The aop will be taking reasonable
+ * precautions not to livelock. If the caller held a page
+ * reference, it should drop it before retrying. Returned
+ * by readpage(), prepare_write(), and commit_write().
+ *
+ * address_space_operation functions return these large constants to indicate
+ * special semantics to the caller. These are much larger than the bytes in a
+ * page to allow for functions that return the number of bytes operated on in a
+ * given page.
+ */
+
+enum positive_aop_returns {
+ AOP_WRITEPAGE_ACTIVATE = 0x80000,
+ AOP_TRUNCATED_PAGE = 0x80001,
+};
+
/*
* oh the beauties of C type declarations.
*/