[RFC PATCH 56/61] afs: Copy local writes to the cache when writing to the server

[David Howells <dhowells@redhat.com>]

When writing to the server from afs_writepage() or afs_writepages(), copy
the data to the cache object too.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/afs/write.c |  124 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 119 insertions(+), 5 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 312d8f07533e..38637dc6043c 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -13,6 +13,9 @@
 #include <linux/pagevec.h>
 #include "internal.h"
 
+static void afs_write_to_cache(struct afs_vnode *vnode,
+			       pgoff_t start, pgoff_t end, loff_t a, loff_t b);
+
 /*
  * mark a page as having been made dirty and thus needing writeback
  */
@@ -389,6 +392,8 @@ static int afs_write_back_from_locked_page(struct address_space *mapping,
 	count = 1;
 	if (test_set_page_writeback(primary_page))
 		BUG();
+	if (TestSetPageFsCache(primary_page))
+		BUG();
 
 	/* Find all consecutive lockable dirty pages that have contiguous
 	 * written regions, stopping when we find a page that is not
@@ -437,7 +442,8 @@ static int afs_write_back_from_locked_page(struct address_space *mapping,
 				break;
 			if (!trylock_page(page))
 				break;
-			if (!PageDirty(page) || PageWriteback(page)) {
+			if (!PageDirty(page) || PageWriteback(page) ||
+			    PageFsCache(page)) {
 				unlock_page(page);
 				break;
 			}
@@ -459,6 +465,8 @@ static int afs_write_back_from_locked_page(struct address_space *mapping,
 				BUG();
 			if (test_set_page_writeback(page))
 				BUG();
+			if (TestSetPageFsCache(page))
+				BUG();
 			unlock_page(page);
 			put_page(page);
 		}
@@ -489,8 +497,13 @@ static int afs_write_back_from_locked_page(struct address_space *mapping,
 	b = last;
 	b <<= PAGE_SHIFT;
 	b += to;
-	iov_iter_mapping(&iter, WRITE, mapping, a, b - a);
 
+	/* Speculatively write to the cache.  We have to fix this up later if
+	 * the store fails.
+	 */
+	afs_write_to_cache(vnode, first, last + 1, a, b);
+
+	iov_iter_mapping(&iter, WRITE, mapping, a, b - a);
 	ret = afs_store_data(vnode, &iter, a, first, last);
 	switch (ret) {
 	case 0:
@@ -543,6 +556,10 @@ int afs_writepage(struct page *page, struct writeback_control *wbc)
 
 	_enter("{%lx},", page->index);
 
+#ifdef CONFIG_AFS_FSCACHE
+	wait_on_page_fscache(page);
+#endif
+
 	ret = afs_write_back_from_locked_page(page->mapping, wbc, page,
 					      wbc->range_end >> PAGE_SHIFT);
 	if (ret < 0) {
@@ -570,7 +587,7 @@ static int afs_writepages_region(struct address_space *mapping,
 
 	do {
 		n = find_get_pages_range_tag(mapping, &index, end,
-					PAGECACHE_TAG_DIRTY, 1, &page);
+					     PAGECACHE_TAG_DIRTY, 1, &page);
 		if (!n)
 			break;
 
@@ -595,10 +612,14 @@ static int afs_writepages_region(struct address_space *mapping,
 			continue;
 		}
 
-		if (PageWriteback(page)) {
+		if (PageWriteback(page) || PageFsCache(page)) {
 			unlock_page(page);
-			if (wbc->sync_mode != WB_SYNC_NONE)
+			if (wbc->sync_mode != WB_SYNC_NONE) {
 				wait_on_page_writeback(page);
+#ifdef CONFIG_AFS_FSCACHE
+				wait_on_page_fscache(page);
+#endif
+			}
 			put_page(page);
 			continue;
 		}
@@ -818,3 +839,96 @@ int afs_launder_page(struct page *page)
 	ClearPagePrivate(page);
 	return ret;
 }
+
+/*
+ * Clear the PG_fscache flag from a sequence of pages and wake up anyone who's
+ * waiting.  The last page is included in the sequence.
+ */
+static void afs_clear_fscache_bits(struct address_space *mapping,
+				   pgoff_t start, pgoff_t last)
+{
+	struct page *page;
+
+	XA_STATE(xas, &mapping->i_pages, start);
+
+	rcu_read_lock();
+	xas_for_each(&xas, page, last) {
+		unlock_page_fscache(page);
+	}
+	rcu_read_unlock();
+}
+
+/*
+ * Deal with the completion of writing the data to the cache.
+ */
+static void afs_write_to_cache_done(struct fscache_io_request *_req)
+{
+	struct afs_read *req = container_of(_req, struct afs_read, cache);
+	pgoff_t index = req->cache.pos >> PAGE_SHIFT;
+	pgoff_t last = index + req->cache.nr_pages - 1;
+
+	_enter("%lx,%x,%llx", index, req->cache.nr_pages, req->cache.transferred);
+
+	afs_clear_fscache_bits(req->cache.mapping, index, last);
+
+	if (req->cache.error && req->cache.error != -ENOBUFS) {
+		struct afs_vnode *vnode = req->vnode;
+		struct afs_vnode_cache_aux aux = {
+			.data_version = vnode->status.data_version,
+		};
+		_debug("inval wr %d", req->cache.error);
+		fscache_invalidate(req->cache.cookie, &aux,
+				   i_size_read(&vnode->vfs_inode), 0);
+	}
+}
+
+static const struct fscache_io_request_ops afs_write_req_ops = {
+	.get		= afs_req_get,
+	.put		= afs_req_put,
+};
+
+/*
+ * Save the write to the cache also.
+ */
+static void afs_write_to_cache(struct afs_vnode *vnode,
+			       pgoff_t start, pgoff_t end, loff_t a, loff_t b)
+{
+	struct afs_read *req;
+	struct iov_iter iter;
+	unsigned int x;
+
+	struct fscache_extent extent = {
+		.start		= start,
+		.block_end	= end,
+		.limit		= end,
+	};
+
+	_enter("%lx,%lx,%llx,%llx", start, end, a, b);
+
+	x = fscache_shape_extent(afs_vnode_cache(vnode), &extent,
+				 i_size_read(&vnode->vfs_inode), true);
+	if (!(x & FSCACHE_WRITE_TO_CACHE))
+		goto abandon;
+
+	req = afs_alloc_read(GFP_KERNEL);
+	if (!req)
+		goto abandon;
+
+	fscache_init_io_request(&req->cache, afs_vnode_cache(vnode),
+				&afs_write_req_ops);
+	req->vnode		= vnode;
+	req->cache.pos		= round_down(a, extent.dio_block_size);
+	req->cache.len		= round_up(b, extent.dio_block_size) - req->cache.pos;
+	req->cache.nr_pages	= end - start;
+	req->cache.mapping	= vnode->vfs_inode.i_mapping;
+	req->cache.io_done	= &afs_write_to_cache_done;
+
+	iov_iter_mapping(&iter, WRITE, req->cache.mapping,
+			 req->cache.pos, req->cache.len);
+	fscache_write(&req->cache, &iter);
+	afs_put_read(req);
+	return;
+
+abandon:
+	afs_clear_fscache_bits(vnode->vfs_inode.i_mapping, start, end);
+}