[PATCH v7 03/19] cachefiles: notify user daemon when withdrawing cookie

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

Notify user daemon that cookie is going to be withdrawn, providing a
hint that the associated anon_fd can be closed. The anon_fd attached in
the CLOSE request shall be same with that in the previous OPEN request.

Be noted that this is only a hint. User daemon can close the anon_fd
when receiving the CLOSE request, then it will receive another anon_fd
if the cookie gets looked up. Or it can also ignore the CLOSE request,
and keep writing data into the anon_fd. However the next time cookie
gets looked up, the user daemon will still receive another anon_fd.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/cachefiles/interface.c       |  2 ++
 fs/cachefiles/internal.h        |  5 +++++
 fs/cachefiles/ondemand.c        | 34 +++++++++++++++++++++++++++++++++
 include/uapi/linux/cachefiles.h |  5 +++++
 4 files changed, 46 insertions(+)

diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index ae93cee9d25d..a69073a1d3f0 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -362,6 +362,8 @@ static void cachefiles_withdraw_cookie(struct fscache_cookie *cookie)
 		spin_unlock(&cache->object_list_lock);
 	}
 
+	cachefiles_ondemand_clean_object(object);
+
 	if (object->file) {
 		cachefiles_begin_secure(cache, &saved_cred);
 		cachefiles_clean_up_object(object, cache);
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index 7d5c7d391fdb..8a397d4da560 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -279,6 +279,7 @@ extern int cachefiles_ondemand_copen(struct cachefiles_cache *cache,
 				     char *args);
 
 extern int cachefiles_ondemand_init_object(struct cachefiles_object *object);
+extern void cachefiles_ondemand_clean_object(struct cachefiles_object *object);
 
 #else
 static inline ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
@@ -291,6 +292,10 @@ static inline int cachefiles_ondemand_init_object(struct cachefiles_object *obje
 {
 	return 0;
 }
+
+static inline void cachefiles_ondemand_clean_object(struct cachefiles_object *object)
+{
+}
 #endif
 
 /*
diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index f0e6e422263b..8cbfba057616 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -209,6 +209,12 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
 		goto err_put_fd;
 	}
 
+	/* CLOSE request has no reply */
+	if (msg->opcode == CACHEFILES_OP_CLOSE) {
+		xa_erase(&cache->reqs, id);
+		complete(&req->done);
+	}
+
 	return n;
 
 err_put_fd:
@@ -332,6 +338,26 @@ static int init_open_req(struct cachefiles_req *req, void *private)
 	return 0;
 }
 
+static int init_close_req(struct cachefiles_req *req, void *private)
+{
+	struct cachefiles_object *object = req->object;
+	struct cachefiles_close *load = (void *)req->msg.data;
+	int fd = object->fd;
+
+	if (WARN_ON_ONCE(fd == -1))
+		return -EIO;
+
+	/*
+	 * It's possible if the cookie looking up phase failed before READ
+	 * request has ever been sent.
+	 */
+	if (fd == 0)
+		return -ENOENT;
+
+	load->fd = fd;
+	return 0;
+}
+
 int cachefiles_ondemand_init_object(struct cachefiles_object *object)
 {
 	struct fscache_cookie *cookie = object->cookie;
@@ -356,3 +382,11 @@ int cachefiles_ondemand_init_object(struct cachefiles_object *object)
 					    CACHEFILES_OP_OPEN, data_len,
 					    init_open_req, NULL);
 }
+
+void cachefiles_ondemand_clean_object(struct cachefiles_object *object)
+{
+	cachefiles_ondemand_send_req(object,
+				     CACHEFILES_OP_CLOSE,
+				     sizeof(struct cachefiles_close),
+				     init_close_req, NULL);
+}
diff --git a/include/uapi/linux/cachefiles.h b/include/uapi/linux/cachefiles.h
index 49cb7adb439a..dba97d284899 100644
--- a/include/uapi/linux/cachefiles.h
+++ b/include/uapi/linux/cachefiles.h
@@ -12,6 +12,7 @@
 
 enum cachefiles_opcode {
 	CACHEFILES_OP_OPEN,
+	CACHEFILES_OP_CLOSE,
 };
 
 /*
@@ -36,4 +37,8 @@ struct cachefiles_open {
 	__u8  data[];
 };
 
+struct cachefiles_close {
+	__u32 fd;
+};
+
 #endif
-- 
2.27.0