CacheFiles: Permit the page lock state to be monitored

Add a function to install a monitor on the page lock waitqueue for a particular
page, thus allowing the page being unlocked to be detected.

This is used by CacheFiles to detect read completion on a page in the backing
filesystem so that it can then copy the data to the waiting netfs page.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 076a7dc67c2bd25c89bec24ce036d719f1886dc3..34da5230faab4617cfe9bba4c43ac83cc083ab12 100644 (file)
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -383,6 +383,11 @@ static inline void wait_on_page_writeback(struct page *page)
 
 extern void end_page_writeback(struct page *page);
 
+/*
+ * Add an arbitrary waiter to a page's wait queue
+ */
+extern void add_page_wait_queue(struct page *page, wait_queue_t *waiter);
+
 /*
  * Fault a userspace page into pagetables.  Return non-zero on a fault.
  *

diff --git a/mm/filemap.c b/mm/filemap.c
index cbc5772e7171fbc7e074dae51743a6f2d5168d91..fc11974f2bee5ea0d39941f3dfce8b0b84910579 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -564,6 +564,24 @@ void wait_on_page_bit(struct page *page, int bit_nr)
 }
 EXPORT_SYMBOL(wait_on_page_bit);
 
+/**
+ * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
+ * @page - Page defining the wait queue of interest
+ * @waiter - Waiter to add to the queue
+ *
+ * Add an arbitrary @waiter to the wait queue for the nominated @page.
+ */
+void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
+{
+       wait_queue_head_t *q = page_waitqueue(page);
+       unsigned long flags;
+
+       spin_lock_irqsave(&q->lock, flags);
+       __add_wait_queue(q, waiter);
+       spin_unlock_irqrestore(&q->lock, flags);
+}
+EXPORT_SYMBOL_GPL(add_page_wait_queue);
+
 /**
  * unlock_page - unlock a locked page
  * @page: the page