[PATCH v4 12/21] erofs: add anonymous inode managing page cache of blob file

[Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxx>
---
 fs/erofs/fscache.c  | 45 ++++++++++++++++++++++++++++++++++++++++++---
 fs/erofs/internal.h |  3 ++-
 2 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 77d2b46e7ff1..4d83125ff896 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -6,6 +6,9 @@
 
 static struct fscache_volume *volume;
 
+static const struct address_space_operations erofs_fscache_blob_aops = {
+};
+
 static int erofs_fscache_init_cookie(struct erofs_fscache_context *ctx,
 				     char *path)
 {
@@ -36,8 +39,34 @@ void erofs_fscache_cleanup_cookie(struct erofs_fscache_context *ctx)
 	ctx->cookie = NULL;
 }
 
+static int erofs_fscache_get_inode(struct erofs_fscache_context *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_blob_aops;
+	mapping_set_gfp_mask(inode->i_mapping,
+			GFP_NOFS | __GFP_HIGHMEM | __GFP_MOVABLE);
+	ctx->inode = inode;
+	return 0;
+}
+
+static inline
+void erofs_fscache_put_inode(struct erofs_fscache_context *ctx)
+{
+	iput(ctx->inode);
+	ctx->inode = NULL;
+}
+
 static int erofs_fscache_init_ctx(struct erofs_fscache_context *ctx,
-				  struct super_block *sb, char *path)
+				  struct super_block *sb, char *path,
+				  bool need_inode)
 {
 	int ret;
 
@@ -47,6 +76,15 @@ static int erofs_fscache_init_ctx(struct erofs_fscache_context *ctx,
 		return ret;
 	}
 
+	if (need_inode) {
+		ret = erofs_fscache_get_inode(ctx, sb);
+		if (ret) {
+			erofs_err(sb, "failed to get anonymous inode");
+			erofs_fscache_cleanup_cookie(ctx);
+			return ret;
+		}
+	}
+
 	return 0;
 }
 
@@ -54,10 +92,11 @@ static inline
 void erofs_fscache_cleanup_ctx(struct erofs_fscache_context *ctx)
 {
 	erofs_fscache_cleanup_cookie(ctx);
+	erofs_fscache_put_inode(ctx);
 }
 
 struct erofs_fscache_context *erofs_fscache_get_ctx(struct super_block *sb,
-						char *path)
+						char *path, bool need_inode)
 {
 	struct erofs_fscache_context *ctx;
 	int ret;
@@ -66,7 +105,7 @@ struct erofs_fscache_context *erofs_fscache_get_ctx(struct super_block *sb,
 	if (!ctx)
 		return ERR_PTR(-ENOMEM);
 
-	ret = erofs_fscache_init_ctx(ctx, sb, path);
+	ret = erofs_fscache_init_ctx(ctx, sb, path, need_inode);
 	if (ret) {
 		kfree(ctx);
 		return ERR_PTR(ret);
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 1f5bc69e8e9f..bb5e992fe0df 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -99,6 +99,7 @@ struct erofs_sb_lz4_info {
 
 struct erofs_fscache_context {
 	struct fscache_cookie *cookie;
+	struct inode *inode;
 };
 
 struct erofs_sb_info {
@@ -626,7 +627,7 @@ int erofs_init_fscache(void);
 void erofs_exit_fscache(void);
 
 struct erofs_fscache_context *erofs_fscache_get_ctx(struct super_block *sb,
-						char *path);
+						char *path, bool need_inode);
 void erofs_fscache_put_ctx(struct erofs_fscache_context *ctx);
 
 #define EFSCORRUPTED    EUCLEAN         /* Filesystem is corrupted */
-- 
2.27.0