[PATCH v1 10/23] erofs: add anonymous inode managing page cache of blob file

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

Introduce one anonymous inode for managing page cache of corresponding
blob file. Then erofs could read directly from the address space of the
anonymous inode when cache hit.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/erofs/fscache.c  | 35 +++++++++++++++++++++++++++++++++++
 fs/erofs/internal.h |  1 +
 2 files changed, 36 insertions(+)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 15c5bb0f8ea5..4dfca7c95710 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -34,6 +34,33 @@ static void erofs_fscache_cleanup_cookie(struct erofs_cookie_ctx *ctx)
 	ctx->cookie = NULL;
 }
 
+static const struct address_space_operations erofs_fscache_aops = {
+};
+
+static int erofs_fscache_get_inode(struct erofs_cookie_ctx *ctx,
+				   struct super_block *sb)
+{
+	struct inode *const inode = new_inode(sb);
+
+	if (!inode)
+		return -ENOMEM;
+
+	set_nlink(inode, 1);
+	inode->i_size = OFFSET_MAX;
+
+	inode->i_mapping->a_ops = &erofs_fscache_aops;
+	mapping_set_gfp_mask(inode->i_mapping,
+			GFP_NOFS | __GFP_HIGHMEM | __GFP_MOVABLE);
+	ctx->inode = inode;
+	return 0;
+}
+
+static void erofs_fscache_put_inode(struct erofs_cookie_ctx *ctx)
+{
+	iput(ctx->inode);
+	ctx->inode = NULL;
+}
+
 static int erofs_fscahce_init_ctx(struct erofs_cookie_ctx *ctx,
 				  struct super_block *sb, char *path)
 {
@@ -45,12 +72,20 @@ static int erofs_fscahce_init_ctx(struct erofs_cookie_ctx *ctx,
 		return ret;
 	}
 
+	ret = erofs_fscache_get_inode(ctx, sb);
+	if (ret) {
+		erofs_err(sb, "failed to get anonymous inode\n");
+		erofs_fscache_cleanup_cookie(ctx);
+		return ret;
+	}
+
 	return 0;
 }
 
 static void erofs_fscache_cleanup_ctx(struct erofs_cookie_ctx *ctx)
 {
 	erofs_fscache_cleanup_cookie(ctx);
+	erofs_fscache_put_inode(ctx);
 }
 
 struct erofs_cookie_ctx *erofs_fscache_get_ctx(struct super_block *sb,
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 4179c3dcb7f9..2e4f267b37e7 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -93,6 +93,7 @@ struct erofs_sb_lz4_info {
 
 struct erofs_cookie_ctx {
 	struct fscache_cookie *cookie;
+	struct inode *inode;
 };
 
 struct erofs_sb_info {
-- 
2.27.0