Squashfs: refactor page_actor

This patch essentially does 3 things:
  1/ Always use an array of page to store the data instead of a mix of
     buffers and pages.
  2/ It is now possible to have 'holes' in a page actor, i.e. NULL
     pages in the array.
     When reading a block (default 128K), squashfs tries to grab all
     the pages covering this block. If a single page is up-to-date or
     locked, it falls back to using an intermediate buffer to do the
     read and then copy the pages in the actor. Allowing holes in the
     page actor remove the need for this intermediate buffer.
  3/ Refactor the wrappers to share code that deals with page actors.

Signed-off-by: Adrien Schildknecht <adriens@google.com>
Change-Id: I73f736611766962857c423320478af8cfab8df38

1 files changed, 114 insertions, 61 deletions

diff --git a/fs/squashfs/page_actor.c b/fs/squashfs/page_actor.c
index 5a1c11f56..ee1ade20f 100644
--- a/fs/squashfs/page_actor.c
+++ b/fs/squashfs/page_actor.c
@@ -9,92 +9,145 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/pagemap.h>
+#include <linux/buffer_head.h>
 #include "page_actor.h"
 
-/*
- * This file contains implementations of page_actor for decompressing into
- * an intermediate buffer, and for decompressing directly into the
- * page cache.
- *
- * Calling code should avoid sleeping between calls to squashfs_first_page()
- * and squashfs_finish_page().
- */
-
-/* Implementation of page_actor for decompressing into intermediate buffer */
-static void *cache_first_page(struct squashfs_page_actor *actor)
+struct squashfs_page_actor *squashfs_page_actor_init(struct page **page,
+	int pages, int length, void (*release_pages)(struct page **, int, int))
 {
-	actor->next_page = 1;
-	return actor->buffer[0];
-}
+	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
 
-static void *cache_next_page(struct squashfs_page_actor *actor)
-{
-	if (actor->next_page == actor->pages)
+	if (actor == NULL)
 		return NULL;
 
-	return actor->buffer[actor->next_page++];
+	actor->length = length ? : pages * PAGE_SIZE;
+	actor->page = page;
+	actor->pages = pages;
+	actor->next_page = 0;
+	actor->pageaddr = NULL;
+	actor->release_pages = release_pages;
+	return actor;
 }
 
-static void cache_finish_page(struct squashfs_page_actor *actor)
+void squashfs_page_actor_free(struct squashfs_page_actor *actor, int error)
 {
-	/* empty */
+	if (!actor)
+		return;
+
+	if (actor->release_pages)
+		actor->release_pages(actor->page, actor->pages, error);
+	kfree(actor);
 }
 
-struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
-	int pages, int length)
+void squashfs_actor_to_buf(struct squashfs_page_actor *actor, void *buf,
+	int length)
 {
-	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
-
-	if (actor == NULL)
-		return NULL;
-
-	actor->length = length ? : pages * PAGE_CACHE_SIZE;
-	actor->buffer = buffer;
-	actor->pages = pages;
-	actor->next_page = 0;
-	actor->squashfs_first_page = cache_first_page;
-	actor->squashfs_next_page = cache_next_page;
-	actor->squashfs_finish_page = cache_finish_page;
-	return actor;
+	void *pageaddr;
+	int i, avail, pos = 0;
+
+	for (i = 0; i < actor->pages && pos < length; ++i) {
+		avail = min_t(int, length - pos, PAGE_SIZE);
+		if (actor->page[i]) {
+			pageaddr = kmap_atomic(actor->page[i]);
+			memcpy(buf + pos, pageaddr, avail);
+			kunmap_atomic(pageaddr);
+		}
+		pos += avail;
+	}
 }
 
-/* Implementation of page_actor for decompressing directly into page cache. */
-static void *direct_first_page(struct squashfs_page_actor *actor)
+void squashfs_buf_to_actor(void *buf, struct squashfs_page_actor *actor,
+	int length)
 {
-	actor->next_page = 1;
-	return actor->pageaddr = kmap_atomic(actor->page[0]);
+	void *pageaddr;
+	int i, avail, pos = 0;
+
+	for (i = 0; i < actor->pages && pos < length; ++i) {
+		avail = min_t(int, length - pos, PAGE_SIZE);
+		if (actor->page[i]) {
+			pageaddr = kmap_atomic(actor->page[i]);
+			memcpy(pageaddr, buf + pos, avail);
+			kunmap_atomic(pageaddr);
+		}
+		pos += avail;
+	}
 }
 
-static void *direct_next_page(struct squashfs_page_actor *actor)
+void squashfs_bh_to_actor(struct buffer_head **bh, int nr_buffers,
+	struct squashfs_page_actor *actor, int offset, int length, int blksz)
 {
-	if (actor->pageaddr)
-		kunmap_atomic(actor->pageaddr);
+	void *kaddr = NULL;
+	int bytes = 0, pgoff = 0, b = 0, p = 0, i, avail;
+
+	while (bytes < length) {
+		if (actor->page[p]) {
+			kaddr = kmap_atomic(actor->page[p]);
+			while (pgoff < PAGE_SIZE && bytes < length) {
+				avail = min_t(int, blksz - offset,
+						PAGE_SIZE - pgoff);
+				memcpy(kaddr + pgoff, bh[b]->b_data + offset,
+				       avail);
+				pgoff += avail;
+				bytes += avail;
+				offset = (offset + avail) % blksz;
+				if (!offset) {
+					put_bh(bh[b]);
+					++b;
+				}
+			}
+			kunmap_atomic(kaddr);
+			pgoff = 0;
+		} else {
+			for (i = 0; i < PAGE_SIZE / blksz; ++i) {
+				if (bh[b])
+					put_bh(bh[b]);
+				++b;
+			}
+			bytes += PAGE_SIZE;
+		}
+		++p;
+	}
+}
 
-	return actor->pageaddr = actor->next_page == actor->pages ? NULL :
-		kmap_atomic(actor->page[actor->next_page++]);
+void squashfs_bh_to_buf(struct buffer_head **bh, int nr_buffers, void *buf,
+	int offset, int length, int blksz)
+{
+	int i, avail, bytes = 0;
+
+	for (i = 0; i < nr_buffers && bytes < length; ++i) {
+		avail = min_t(int, length - bytes, blksz - offset);
+		if (bh[i]) {
+			memcpy(buf + bytes, bh[i]->b_data + offset, avail);
+			put_bh(bh[i]);
+		}
+		bytes += avail;
+		offset = 0;
+	}
 }
 
-static void direct_finish_page(struct squashfs_page_actor *actor)
+void free_page_array(struct page **page, int nr_pages)
 {
-	if (actor->pageaddr)
-		kunmap_atomic(actor->pageaddr);
+	int i;
+
+	for (i = 0; i < nr_pages; ++i)
+		__free_page(page[i]);
+	kfree(page);
 }
 
-struct squashfs_page_actor *squashfs_page_actor_init_special(struct page **page,
-	int pages, int length)
+struct page **alloc_page_array(int nr_pages, int gfp_mask)
 {
-	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
+	int i;
+	struct page **page;
 
-	if (actor == NULL)
+	page = kcalloc(nr_pages, sizeof(struct page *), gfp_mask);
+	if (!page)
 		return NULL;
-
-	actor->length = length ? : pages * PAGE_CACHE_SIZE;
-	actor->page = page;
-	actor->pages = pages;
-	actor->next_page = 0;
-	actor->pageaddr = NULL;
-	actor->squashfs_first_page = direct_first_page;
-	actor->squashfs_next_page = direct_next_page;
-	actor->squashfs_finish_page = direct_finish_page;
-	return actor;
+	for (i = 0; i < nr_pages; ++i) {
+		page[i] = alloc_page(gfp_mask);
+		if (!page[i]) {
+			free_page_array(page, i);
+			return NULL;
+		}
+	}
+	return page;
 }