[PATCH 09/11] splice: use get_page_for_read()

[Miklos Szeredi]

What __generic_file_splice_read() does is get a series of uptodate pages
and put them into the pipe buffer.

The get_page_for_read() helper can now be used to get the pages,
simplifying the code and making sure the splice(2) stays in sync with
read(2).

For example get_page_for_read() can handle partially uptodate pages and now
splice can take advantage of these as well.

Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
---
 fs/splice.c | 169 +++++-------------------------------------------------------
 1 file changed, 12 insertions(+), 157 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index dc4648ba6e8d..e7757b363b6c 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -265,14 +265,12 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 			   struct pipe_inode_info *pipe, size_t len,
 			   unsigned int flags)
 {
-	struct address_space *mapping = in->f_mapping;
 	unsigned int loff, nr_pages, req_pages;
 	struct page *pages[PIPE_DEF_BUFFERS];
 	struct partial_page partial[PIPE_DEF_BUFFERS];
 	struct page *page;
-	pgoff_t index, end_index;
-	loff_t isize;
-	int error, page_nr;
+	pgoff_t index;
+	int error;
 	struct splice_pipe_desc spd = {
 		.pages = pages,
 		.partial = partial,
@@ -290,168 +288,25 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 	req_pages = (len + loff + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	nr_pages = min(req_pages, spd.nr_pages_max);
 
-	/*
-	 * Lookup the (hopefully) full range of pages we need.
-	 */
-	spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, spd.pages);
-	index += spd.nr_pages;
-
-	/*
-	 * If find_get_pages_contig() returned fewer pages than we needed,
-	 * readahead/allocate the rest and fill in the holes.
-	 */
-	if (spd.nr_pages < nr_pages)
-		page_cache_sync_readahead(mapping, &in->f_ra, in,
-				index, req_pages - spd.nr_pages);
-
 	error = 0;
-	while (spd.nr_pages < nr_pages) {
-		/*
-		 * Page could be there, find_get_pages_contig() breaks on
-		 * the first hole.
-		 */
-		page = find_get_page(mapping, index);
-		if (!page) {
-			/*
-			 * page didn't exist, allocate one.
-			 */
-			page = page_cache_alloc_cold(mapping);
-			if (!page)
-				break;
+	while (spd.nr_pages < nr_pages && len) {
+		long ret;
 
-			error = add_to_page_cache_lru(page, mapping, index,
-				   mapping_gfp_constraint(mapping, GFP_KERNEL));
-			if (unlikely(error)) {
-				put_page(page);
-				if (error == -EEXIST)
-					continue;
-				break;
-			}
-			/*
-			 * add_to_page_cache() locks the page, unlock it
-			 * to avoid convoluting the logic below even more.
-			 */
-			unlock_page(page);
-		}
-
-		spd.pages[spd.nr_pages++] = page;
-		index++;
-	}
-
-	/*
-	 * Now loop over the map and see if we need to start IO on any
-	 * pages, fill in the partial map, etc.
-	 */
-	index = *ppos >> PAGE_SHIFT;
-	nr_pages = spd.nr_pages;
-	spd.nr_pages = 0;
-	for (page_nr = 0; page_nr < nr_pages; page_nr++) {
-		unsigned int this_len;
-
-		if (!len)
+		ret = get_page_for_read(in, loff, len, index, &page);
+		if (ret <= 0) {
+			error = ret;
 			break;
-
-		/*
-		 * this_len is the max we'll use from this page
-		 */
-		this_len = min_t(unsigned long, len, PAGE_SIZE - loff);
-		page = spd.pages[page_nr];
-
-		if (PageReadahead(page))
-			page_cache_async_readahead(mapping, &in->f_ra, in,
-					page, index, req_pages - page_nr);
-
-		/*
-		 * If the page isn't uptodate, we may need to start io on it
-		 */
-		if (!PageUptodate(page)) {
-			lock_page(page);
-
-			/*
-			 * Page was truncated, or invalidated by the
-			 * filesystem.  Redo the find/create, but this time the
-			 * page is kept locked, so there's no chance of another
-			 * race with truncate/invalidate.
-			 */
-			if (!page->mapping) {
-				unlock_page(page);
-retry_lookup:
-				page = find_or_create_page(mapping, index,
-						mapping_gfp_mask(mapping));
-
-				if (!page) {
-					error = -ENOMEM;
-					break;
-				}
-				put_page(spd.pages[page_nr]);
-				spd.pages[page_nr] = page;
-			}
-			/*
-			 * page was already under io and is now done, great
-			 */
-			if (PageUptodate(page)) {
-				unlock_page(page);
-				goto fill_it;
-			}
-
-			/*
-			 * need to read in the page
-			 */
-			error = mapping->a_ops->readpage(in, page);
-			if (unlikely(error)) {
-				/*
-				 * Re-lookup the page
-				 */
-				if (error == AOP_TRUNCATED_PAGE)
-					goto retry_lookup;
-
-				break;
-			}
-		}
-fill_it:
-		/*
-		 * i_size must be checked after PageUptodate.
-		 */
-		isize = i_size_read(mapping->host);
-		end_index = (isize - 1) >> PAGE_SHIFT;
-		if (unlikely(!isize || index > end_index))
-			break;
-
-		/*
-		 * if this is the last page, see if we need to shrink
-		 * the length and stop
-		 */
-		if (end_index == index) {
-			unsigned int plen;
-
-			/*
-			 * max good bytes in this page
-			 */
-			plen = ((isize - 1) & ~PAGE_MASK) + 1;
-			if (plen <= loff)
-				break;
-
-			/*
-			 * force quit after adding this page
-			 */
-			this_len = min(this_len, plen - loff);
-			len = this_len;
 		}
 
-		spd.partial[page_nr].offset = loff;
-		spd.partial[page_nr].len = this_len;
-		len -= this_len;
-		loff = 0;
+		spd.pages[spd.nr_pages] = page;
+		spd.partial[spd.nr_pages].offset = loff;
+		spd.partial[spd.nr_pages].len = ret;
 		spd.nr_pages++;
 		index++;
+		len -= ret;
+		loff = 0;
 	}
 
-	/*
-	 * Release any pages at the end, if we quit early. 'page_nr' is how far
-	 * we got, 'nr_pages' is how many pages are in the map.
-	 */
-	while (page_nr < nr_pages)
-		put_page(spd.pages[page_nr++]);
 	in->f_ra.prev_pos = (loff_t)index << PAGE_SHIFT;
 
 	if (spd.nr_pages)
-- 
2.5.5