[NOMERGE] [RFC PATCH 04/12] erofs: add raw address_space operations

[Gao Xiang]

This commit adds functions for meta and raw data, providing
a set of raw address_space_operations for file inodes.

Signed-off-by: Miao Xie <miaoxie@xxxxxxxxxx>
Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
---
 fs/erofs/data.c | 393 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 393 insertions(+)
 create mode 100644 fs/erofs/data.c

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
new file mode 100644
index 0000000..9b30095
--- /dev/null
+++ b/fs/erofs/data.c
@@ -0,0 +1,393 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/erofs/data.c
+ *
+ * Copyright (C) 2017-2018 HUAWEI, Inc.
+ *             http://www.huawei.com/
+ * Created by Gao Xiang <gaoxiang25@xxxxxxxxxx>
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of the Linux
+ * distribution for more details.
+ */
+#include "internal.h"
+
+#if (LINUX_VERSION_CODE < KERNEL_VERSION(4, 3, 0))
+static inline void read_endio(struct bio *bio, int err)
+#else
+static inline void read_endio(struct bio *bio)
+#endif
+{
+	int i;
+	struct bio_vec *bvec;
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(4, 13, 0))
+	const int err = bio->bi_status;
+#elif (LINUX_VERSION_CODE >= KERNEL_VERSION(4, 3, 0))
+	const int err = bio->bi_error;
+#endif
+
+	bio_for_each_segment_all(bvec, bio, i) {
+		struct page *page = bvec->bv_page;
+
+		/* page is already locked */
+		BUG_ON(PageUptodate(page));
+
+		if (unlikely(err))
+			SetPageError(page);
+		else
+			SetPageUptodate(page);
+
+		unlock_page(page);
+		/* page could be reclaimed now */
+	}
+	bio_put(bio);
+}
+
+static void __submit_bio(struct bio *bio, unsigned op, unsigned op_flags)
+{
+	bio_set_op_attrs(bio, op, op_flags);
+#if (LINUX_VERSION_CODE < KERNEL_VERSION(4, 8, 0))
+	submit_bio(0, bio);
+#else
+	submit_bio(bio);
+#endif
+}
+
+static struct bio *prepare_bio(struct super_block *sb,
+	erofs_blk_t blkaddr, unsigned nr_pages)
+{
+	struct bio *bio = bio_alloc(GFP_NOIO | __GFP_NOFAIL, nr_pages);
+
+	BUG_ON(bio == NULL);
+
+	bio->bi_end_io = read_endio;
+	bio_set_dev(bio, sb->s_bdev);
+#if (LINUX_VERSION_CODE < KERNEL_VERSION(3, 14, 0))
+	bio->bi_sector = blkaddr << LOG_SECTORS_PER_BLOCK;
+#else
+	bio->bi_iter.bi_sector = blkaddr << LOG_SECTORS_PER_BLOCK;
+#endif
+	return bio;
+}
+
+/* prio -- true is used for dir */
+struct page *erofs_get_meta_page(struct super_block *sb,
+	erofs_blk_t blkaddr, bool prio)
+{
+	struct inode *bd_inode = sb->s_bdev->bd_inode;
+	struct address_space *mapping = bd_inode->i_mapping;
+	struct page *page;
+
+repeat:
+	page = find_or_create_page(mapping, blkaddr,
+	/*
+	 * Prefer looping in the allocator rather than here,
+	 * at least that code knows what it's doing.
+	 */
+		mapping_gfp_constraint(mapping, ~__GFP_FS) | __GFP_NOFAIL);
+
+	BUG_ON(!page || !PageLocked(page));
+
+	if (!PageUptodate(page)) {
+		struct bio *bio;
+		int err;
+
+		bio = prepare_bio(sb, blkaddr, 1);
+		err = bio_add_page(bio, page, PAGE_SIZE, 0);
+		BUG_ON(err != PAGE_SIZE);
+
+		__submit_bio(bio, REQ_OP_READ,
+			REQ_META | (prio ? REQ_PRIO : 0));
+
+		lock_page(page);
+
+		/* the page has been truncated by others? */
+		if (unlikely(page->mapping != mapping)) {
+			unlock_page(page);
+			put_page(page);
+			goto repeat;
+		}
+
+		/* more likely a read error */
+		if (unlikely(!PageUptodate(page))) {
+			unlock_page(page);
+			put_page(page);
+
+			page = ERR_PTR(-EIO);
+		}
+	}
+	return page;
+}
+
+#if 0
+/* for debugging use only */
+void test_meta_ops(struct super_block *sb)
+{
+	/* dump the first page */
+	struct page *page = erofs_get_meta_page(sb, 0, false);
+	void *data = page_address(page);
+
+	print_hex_dump(KERN_DEBUG, "raw data: ", DUMP_PREFIX_OFFSET,
+		16, 1, data, PAGE_SIZE, true);
+
+	unlock_page(page);
+	put_page(page);
+}
+#endif
+
+static int erofs_map_blocks_flatmode(struct inode *inode,
+	struct erofs_map_blocks *map,
+	int flags)
+{
+	erofs_blk_t nblocks, lastblk;
+	u64 offset = map->m_la;
+	struct erofs_vnode *vi = EROFS_V(inode);
+
+	BUG_ON(is_inode_layout_compression(inode));
+
+	nblocks = DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
+	lastblk = nblocks - is_inode_layout_inline(inode);
+
+	if (unlikely(offset >= inode->i_size)) {
+		/* leave out-of-bound access unmapped */
+		map->m_flags = 0;
+		map->m_plen = 0;
+		goto out;
+	}
+
+	/* there is no hole in flatmode */
+	map->m_flags = EROFS_MAP_MAPPED;
+
+	if (offset < blknr_to_addr(lastblk)) {
+		map->m_pa = blknr_to_addr(vi->raw_blkaddr) + map->m_la;
+		map->m_plen = blknr_to_addr(lastblk) - offset;
+	} else if (is_inode_layout_inline(inode)) {
+		/* 2 - inode inline B: inode, [xattrs], inline last blk... */
+		struct erofs_sb_info *sbi = EROFS_SB(inode->i_sb);
+
+		map->m_pa = iloc(sbi, vi->nid) + vi->inode_isize +
+			vi->xattr_isize + erofs_blkoff(map->m_la);
+		map->m_plen = inode->i_size - offset;
+
+		/* inline data should locate in one meta block */
+		BUG_ON(erofs_blkoff(map->m_pa) + map->m_plen > PAGE_SIZE);
+		map->m_flags |= EROFS_MAP_META;
+	} else {
+		errln("internal error @ nid: %llu (size %llu), m_la 0x%llx",
+			vi->nid, inode->i_size, map->m_la);
+		BUG();
+	}
+
+out:
+	map->m_llen = map->m_plen;
+	debugln("%s, m_la 0x%llx m_pa %llx m_len %llu",
+		__func__, map->m_la, map->m_pa, map->m_plen);
+	return 0;
+}
+
+int erofs_map_blocks(struct inode *inode,
+	struct erofs_map_blocks *map, int flags)
+{
+	if (!is_inode_layout_compression(inode))
+		return erofs_map_blocks_flatmode(inode, map, flags);
+
+	/* data compression unimplemented yet */
+	return -ENOTSUPP;
+}
+
+static inline struct bio *erofs_read_raw_page(
+	struct bio *bio,
+	struct address_space *mapping,
+	struct page *page,
+	unsigned *last_block,
+	unsigned nblocks,
+	bool ra)
+{
+	struct inode *inode = mapping->host;
+	unsigned current_block = page->index;
+	int err;
+
+	BUG_ON(!nblocks);
+
+	if (PageUptodate(page)) {
+		err = 0;
+		goto has_updated;
+	}
+
+	if (cleancache_get_page(page) == 0) {
+		err = 0;
+		SetPageUptodate(page);
+		goto has_updated;
+	}
+
+	/* note that for readpage case, bio also equals to NULL */
+	if (bio != NULL &&
+		/* not continuous */
+		*last_block + 1 != current_block) {
+submit_bio_retry:
+		__submit_bio(bio, REQ_OP_READ, 0);
+		bio = NULL;
+	}
+
+	if (bio == NULL) {
+		struct erofs_map_blocks map = {
+			.m_la = blknr_to_addr(current_block),
+		};
+
+		err = erofs_map_blocks(inode, &map, EROFS_GET_BLOCKS_RAW);
+		if (unlikely(err))
+			goto err_out;
+
+		/* zero out the holed page */
+		if (unlikely(!(map.m_flags & EROFS_MAP_MAPPED))) {
+			zero_user_segment(page, 0, PAGE_SIZE);
+			SetPageUptodate(page);
+
+			/* imply err = 0, see erofs_map_blocks */
+			goto has_updated;
+		}
+
+		/* for RAW access mode, m_plen must be equal to m_llen */
+		BUG_ON(map.m_plen != map.m_llen);
+
+		/* deal with inline page */
+		if (map.m_flags & EROFS_MAP_META) {
+			void *vsrc, *vto;
+			struct page *ipage;
+
+			BUG_ON(map.m_plen > PAGE_SIZE);
+
+			ipage = erofs_get_meta_page(inode->i_sb,
+				erofs_blknr(map.m_pa), 0);
+
+			if (IS_ERR(ipage)) {
+				err = PTR_ERR(ipage);
+				goto err_out;
+			}
+
+			vsrc = kmap_atomic(ipage);
+			vto = kmap_atomic(page);
+			memcpy(vto, vsrc + erofs_blkoff(map.m_pa), map.m_plen);
+			memset(vto + map.m_plen, 0, PAGE_SIZE - map.m_plen);
+			kunmap_atomic(vto);
+			kunmap_atomic(vsrc);
+			flush_dcache_page(page);
+
+			SetPageUptodate(page);
+			/* TODO: could we unlock the page earlier? */
+			unlock_page(ipage);
+			put_page(ipage);
+
+			/* imply err = 0, see erofs_map_blocks */
+			goto has_updated;
+		}
+
+		/* pa must be block-aligned for raw reading */
+		BUG_ON(erofs_blkoff(map.m_pa) != 0);
+
+		/* max # of continuous pages */
+		if (nblocks > DIV_ROUND_UP(map.m_plen, PAGE_SIZE))
+			nblocks = DIV_ROUND_UP(map.m_plen, PAGE_SIZE);
+		if (nblocks > BIO_MAX_PAGES)
+			nblocks = BIO_MAX_PAGES;
+
+		bio = prepare_bio(inode->i_sb, erofs_blknr(map.m_pa), nblocks);
+	}
+
+	err = bio_add_page(bio, page, PAGE_SIZE, 0);
+	/* out of the extent or bio is full */
+	if (err < PAGE_SIZE)
+		goto submit_bio_retry;
+
+	*last_block = current_block;
+
+	/* shift in advance in case of it followed by too many gaps */
+	if (unlikely(bio->bi_vcnt >= bio->bi_max_vecs)) {
+		/* err should reassign to 0 after submitting */
+		err = 0;
+		goto submit_bio_out;
+	}
+
+	return bio;
+
+err_out:
+	/* for sync reading, set page error immediately */
+	if (!ra) {
+		SetPageError(page);
+		ClearPageUptodate(page);
+	}
+has_updated:
+	unlock_page(page);
+
+	/* if updated manually, continuous pages has a gap */
+	if (bio != NULL)
+submit_bio_out:
+		__submit_bio(bio, REQ_OP_READ, 0);
+
+	return unlikely(err) ? ERR_PTR(err) : NULL;
+}
+
+/*
+ * since we dont have write or truncate flows, so no inode
+ * locking needs to be held at the moment.
+ */
+static int erofs_raw_access_readpage(struct file *file, struct page *page)
+{
+	unsigned last_block;
+	struct bio *bio;
+
+	bio = erofs_read_raw_page(NULL, page->mapping,
+		page, &last_block, 1, false);
+
+	if (IS_ERR(bio))
+		return PTR_ERR(bio);
+
+	BUG_ON(bio != NULL);	/* since we have only one bio -- must be NULL */
+	return 0;
+}
+
+static int erofs_raw_access_readpages(struct file *filp,
+	struct address_space *mapping,
+	struct list_head *pages, unsigned nr_pages)
+{
+	unsigned last_block;
+	struct bio *bio = NULL;
+	gfp_t gfp = readahead_gfp_mask(mapping);
+
+	for (; nr_pages; --nr_pages) {
+		struct page *page = list_entry(pages->prev, struct page, lru);
+
+		prefetchw(&page->flags);
+		list_del(&page->lru);
+
+		if (!add_to_page_cache_lru(page, mapping, page->index, gfp)) {
+			bio = erofs_read_raw_page(bio, mapping, page,
+				&last_block, nr_pages, true);
+
+			/* all the page errors are ignored when readahead */
+			if (IS_ERR(bio)) {
+				pr_err("%s, readahead error at page %lu of nid %llu\n",
+					__func__, page->index,
+					EROFS_V(mapping->host)->nid);
+
+				bio = NULL;
+			}
+		}
+
+		/* pages could still be locked */
+		page_cache_release(page);
+	}
+	BUG_ON(!list_empty(pages));
+
+	/* the rare case (end in gaps) */
+	if (unlikely(bio != NULL))
+		__submit_bio(bio, REQ_OP_READ, 0);
+	return 0;
+}
+
+/* for uncompressed (aligned) files and raw access for other files */
+const struct address_space_operations erofs_raw_access_aops = {
+	.readpage = erofs_raw_access_readpage,
+	.readpages = erofs_raw_access_readpages,
+};
+
-- 
1.9.1