[PATCH v3 10/22] erofs: add cookie context helper functions

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

Introduce 'struct erofs_cookie_ctx' for managing cookie for backing
file, and the following introduced API for reading from backing file.

Besides, introduce two helper functions for initializing and cleaning
up erofs_cookie_ctx.

struct erofs_cookie_ctx *
erofs_fscache_get_ctx(struct super_block *sb, char *path);

void erofs_fscache_put_ctx(struct erofs_cookie_ctx *ctx);

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/erofs/fscache.c  | 78 +++++++++++++++++++++++++++++++++++++++++++++
 fs/erofs/internal.h |  8 +++++
 2 files changed, 86 insertions(+)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 9c32f42e1056..c043d7709d65 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -6,6 +6,84 @@
 
 static struct fscache_volume *volume;
 
+static int erofs_fscache_init_cookie(struct erofs_fscache_context *ctx,
+				     char *path)
+{
+	struct fscache_cookie *cookie;
+
+	/*
+	 * @object_size shall be non-zero to avoid
+	 * FSCACHE_COOKIE_NO_DATA_TO_READ.
+	 */
+	cookie = fscache_acquire_cookie(volume, 0,
+					path, strlen(path),
+					NULL, 0, -1);
+	if (!cookie)
+		return -EINVAL;
+
+	fscache_use_cookie(cookie, false);
+	ctx->cookie = cookie;
+	return 0;
+}
+
+static inline
+void erofs_fscache_cleanup_cookie(struct erofs_fscache_context *ctx)
+{
+	struct fscache_cookie *cookie = ctx->cookie;
+
+	fscache_unuse_cookie(cookie, NULL, NULL);
+	fscache_relinquish_cookie(cookie, false);
+	ctx->cookie = NULL;
+}
+
+static int erofs_fscache_init_ctx(struct erofs_fscache_context *ctx,
+				  struct super_block *sb, char *path)
+{
+	int ret;
+
+	ret = erofs_fscache_init_cookie(ctx, path);
+	if (ret) {
+		erofs_err(sb, "failed to init cookie");
+		return ret;
+	}
+
+	return 0;
+}
+
+static inline
+void erofs_fscache_cleanup_ctx(struct erofs_fscache_context *ctx)
+{
+	erofs_fscache_cleanup_cookie(ctx);
+}
+
+struct erofs_fscache_context *erofs_fscache_get_ctx(struct super_block *sb,
+						char *path)
+{
+	struct erofs_fscache_context *ctx;
+	int ret;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return ERR_PTR(-ENOMEM);
+
+	ret = erofs_fscache_init_ctx(ctx, sb, path);
+	if (ret) {
+		kfree(ctx);
+		return ERR_PTR(ret);
+	}
+
+	return ctx;
+}
+
+void erofs_fscache_put_ctx(struct erofs_fscache_context *ctx)
+{
+	if (!ctx)
+		return;
+
+	erofs_fscache_cleanup_ctx(ctx);
+	kfree(ctx);
+}
+
 int __init erofs_init_fscache(void)
 {
 	volume = fscache_acquire_volume("erofs", NULL, NULL, 0);
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index c2608a469107..1f5bc69e8e9f 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -97,6 +97,10 @@ struct erofs_sb_lz4_info {
 	u16 max_pclusterblks;
 };
 
+struct erofs_fscache_context {
+	struct fscache_cookie *cookie;
+};
+
 struct erofs_sb_info {
 	struct erofs_mount_opts opt;	/* options */
 #ifdef CONFIG_EROFS_FS_ZIP
@@ -621,6 +625,10 @@ static inline int z_erofs_load_lzma_config(struct super_block *sb,
 int erofs_init_fscache(void);
 void erofs_exit_fscache(void);
 
+struct erofs_fscache_context *erofs_fscache_get_ctx(struct super_block *sb,
+						char *path);
+void erofs_fscache_put_ctx(struct erofs_fscache_context *ctx);
+
 #define EFSCORRUPTED    EUCLEAN         /* Filesystem is corrupted */
 
 #endif	/* __EROFS_INTERNAL_H */
-- 
2.27.0