Convert NFS from readpages to readahead

NFS is one of the last two users of the deprecated ->readpages aop.
This conversion looks straightforward, but I have only compile-tested
it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/file.c

@@ -514,7 +514,7 @@ static void nfs_swap_deactivate(struct file *file)
 
 const struct address_space_operations nfs_file_aops = {
 	.readpage = nfs_readpage,
-	.readpages = nfs_readpages,
+	.readahead = nfs_readahead,
 	.set_page_dirty = __set_page_dirty_nobuffers,
 	.writepage = nfs_writepage,
 	.writepages = nfs_writepages,

fs/nfs/nfstrace.h

@@ -889,11 +889,11 @@ TRACE_EVENT(nfs_aop_readpage_done,
 TRACE_EVENT(nfs_aop_readahead,
 		TP_PROTO(
 			const struct inode *inode,
-			struct page *page,
+			loff_t pos,
 			unsigned int nr_pages
 		),
 
-		TP_ARGS(inode, page, nr_pages),
+		TP_ARGS(inode, pos, nr_pages),
 
 		TP_STRUCT__entry(
 			__field(dev_t, dev)
@@ -911,7 +911,7 @@ TRACE_EVENT(nfs_aop_readahead,
 			__entry->fileid = nfsi->fileid;
 			__entry->fhandle = nfs_fhandle_hash(&nfsi->fh);
 			__entry->version = inode_peek_iversion_raw(inode);
-			__entry->offset = page_index(page) << PAGE_SHIFT;
+			__entry->offset = pos;
 			__entry->nr_pages = nr_pages;
 		),
 

fs/nfs/read.c

@@ -290,9 +290,8 @@ static void nfs_readpage_result(struct rpc_task *task,
 }
 
 static int
-readpage_async_filler(void *data, struct page *page)
+readpage_async_filler(struct nfs_readdesc *desc, struct page *page)
 {
-	struct nfs_readdesc *desc = data;
 	struct inode *inode = page_file_mapping(page)->host;
 	unsigned int rsize = NFS_SERVER(inode)->rsize;
 	struct nfs_page *new;
@@ -397,14 +396,16 @@ out_unlock:
 	return ret;
 }
 
-int nfs_readpages(struct file *file, struct address_space *mapping,
-		struct list_head *pages, unsigned nr_pages)
+void nfs_readahead(struct readahead_control *ractl)
 {
+	unsigned int nr_pages = readahead_count(ractl);
+	struct file *file = ractl->file;
 	struct nfs_readdesc desc;
-	struct inode *inode = mapping->host;
+	struct inode *inode = ractl->mapping->host;
+	struct page *page;
 	int ret;
 
-	trace_nfs_aop_readahead(inode, lru_to_page(pages), nr_pages);
+	trace_nfs_aop_readahead(inode, readahead_pos(ractl), nr_pages);
 	nfs_inc_stats(inode, NFSIOS_VFSREADPAGES);
 
 	ret = -ESTALE;
@@ -422,14 +423,18 @@ int nfs_readpages(struct file *file, struct address_space *mapping,
 	nfs_pageio_init_read(&desc.pgio, inode, false,
 			     &nfs_async_read_completion_ops);
 
-	ret = read_cache_pages(mapping, pages, readpage_async_filler, &desc);
+	while ((page = readahead_page(ractl)) != NULL) {
+		ret = readpage_async_filler(&desc, page);
+		put_page(page);
+		if (ret)
+			break;
+	}
 
 	nfs_pageio_complete_read(&desc.pgio);
 
 	put_nfs_open_context(desc.ctx);
 out:
 	trace_nfs_aop_readahead_done(inode, nr_pages, ret);
-	return ret;
 }
 
 int __init nfs_init_readpagecache(void)

include/linux/nfs_fs.h

@@ -601,8 +601,7 @@ nfs_have_writebacks(struct inode *inode)
  * linux/fs/nfs/read.c
  */
 extern int  nfs_readpage(struct file *, struct page *);
-extern int  nfs_readpages(struct file *, struct address_space *,
-		struct list_head *, unsigned);
+void nfs_readahead(struct readahead_control *);
 
 /*
  * inline functions