[PATCH v6 16/22] erofs: implement fscache-based metadata read

[Jeffle Xu <jefflexu@linux.alibaba.com>]

Implements the data plane of reading metadata from bootstrap blob file
over fscache.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/erofs/data.c     | 17 +++++++++++++++--
 fs/erofs/fscache.c  | 34 ++++++++++++++++++++++++++++++++++
 fs/erofs/internal.h |  8 ++++++++
 3 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index 6e2a28242453..b4571bea93d5 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -31,15 +31,28 @@ void erofs_put_metabuf(struct erofs_buf *buf)
 void *erofs_read_metabuf(struct erofs_buf *buf, struct super_block *sb,
 			erofs_blk_t blkaddr, enum erofs_kmap_type type)
 {
-	struct address_space *const mapping = sb->s_bdev->bd_inode->i_mapping;
+	struct address_space *mapping;
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
 	erofs_off_t offset = blknr_to_addr(blkaddr);
 	pgoff_t index = offset >> PAGE_SHIFT;
 	struct page *page = buf->page;
 
 	if (!page || page->index != index) {
 		erofs_put_metabuf(buf);
-		page = read_cache_page_gfp(mapping, index,
+		if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) &&
+		    erofs_is_nodev_mode(sb)) {
+			struct folio *folio;
+
+			folio = erofs_fscache_get_folio(sbi->bootstrap, index);
+			if (IS_ERR(folio))
+				page = (struct page *)folio;
+			else
+				page = folio_page(folio, 0);
+		} else {
+			mapping = sb->s_bdev->bd_inode->i_mapping;
+			page = read_cache_page_gfp(mapping, index,
 				mapping_gfp_constraint(mapping, ~__GFP_FS));
+		}
 		if (IS_ERR(page))
 			return page;
 		/* should already be PageUptodate, no need to lock page */
diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 6a55f7b5f883..91377939b4f7 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -46,9 +46,43 @@ static inline int erofs_fscache_read_folio(struct fscache_cookie *cookie,
 					 pstart);
 }
 
+static int erofs_fscache_readpage_blob(struct file *data, struct page *page)
+{
+	int ret;
+	struct erofs_fscache *ctx = (struct erofs_fscache *)data;
+	struct folio *folio = page_folio(page);
+
+	ret = erofs_fscache_read_folio(ctx->cookie, folio, folio_pos(folio));
+	if (!ret)
+		folio_mark_uptodate(folio);
+
+	folio_unlock(folio);
+	return ret;
+}
+
 static const struct address_space_operations erofs_fscache_blob_aops = {
+	.readpage = erofs_fscache_readpage_blob,
 };
 
+/*
+ * erofs_fscache_get_folio - find and read page cache of blob file
+ * @ctx:	the context of the blob file
+ * @index:	the page index
+ *
+ * Get the page cache of the blob file at the index offset. It will find the
+ * page through the address space of the anonymous inode. This function is only
+ * used to read page cache of bootstrap blob file (metadata), since currently
+ * only bootstrap blob file manages an anonymous inode inside the fscache
+ * context.
+ *
+ * Return: up to date page on success, ERR_PTR() on failure.
+ */
+struct folio *erofs_fscache_get_folio(struct erofs_fscache *ctx, pgoff_t index)
+{
+	DBG_BUGON(!ctx->inode);
+	return read_mapping_folio(ctx->inode->i_mapping, index, ctx);
+}
+
 static int erofs_fscache_init_cookie(struct erofs_fscache *ctx, char *path)
 {
 	struct fscache_cookie *cookie;
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index d8c886a7491e..fa89a1e3012f 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -632,6 +632,8 @@ void erofs_exit_fscache(void);
 struct erofs_fscache *erofs_fscache_get(struct super_block *sb, char *path,
 					bool need_inode);
 void erofs_fscache_put(struct erofs_fscache *ctx);
+
+struct folio *erofs_fscache_get_folio(struct erofs_fscache *ctx, pgoff_t index);
 #else
 static inline int erofs_init_fscache(void) { return 0; }
 static inline void erofs_exit_fscache(void) {}
@@ -643,6 +645,12 @@ static inline struct erofs_fscache *erofs_fscache_get(struct super_block *sb,
 	return ERR_PTR(-EOPNOTSUPP);
 }
 static inline void erofs_fscache_put(struct erofs_fscache *ctx) {}
+
+static inline struct folio *erofs_fscache_get_folio(struct erofs_fscache *ctx,
+						    pgoff_t index)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
 #endif
 
 #define EFSCORRUPTED    EUCLEAN         /* Filesystem is corrupted */
-- 
2.27.0