[PATCH v1 20/23] cachefiles: implement .poll() for demand read

[Jeffle Xu]

User daemon needs to poll on the devnode, and will be notified once
there's pending request to process.

Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
---
 fs/cachefiles/daemon.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index 01496fa8c263..311dcd911a85 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -29,6 +29,8 @@ static ssize_t cachefiles_daemon_write(struct file *, const char __user *,
 				       size_t, loff_t *);
 static __poll_t cachefiles_daemon_poll(struct file *,
 					   struct poll_table_struct *);
+static __poll_t cachefiles_demand_poll(struct file *,
+					   struct poll_table_struct *);
 static int cachefiles_daemon_frun(struct cachefiles_cache *, char *);
 static int cachefiles_daemon_fcull(struct cachefiles_cache *, char *);
 static int cachefiles_daemon_fstop(struct cachefiles_cache *, char *);
@@ -62,6 +64,7 @@ const struct file_operations cachefiles_demand_fops = {
 	.open		= cachefiles_daemon_open,
 	.release	= cachefiles_daemon_release,
 	.write		= cachefiles_daemon_write,
+	.poll		= cachefiles_demand_poll,
 	.llseek		= noop_llseek,
 };
 
@@ -319,6 +322,21 @@ static __poll_t cachefiles_daemon_poll(struct file *file,
 	return mask;
 }
 
+static __poll_t cachefiles_demand_poll(struct file *file,
+					   struct poll_table_struct *poll)
+{
+	struct cachefiles_cache *cache = file->private_data;
+	__poll_t mask;
+
+	poll_wait(file, &cache->daemon_pollwq, poll);
+	mask = 0;
+
+	if (!idr_is_empty(&cache->reqs))
+		mask |= EPOLLIN;
+
+	return mask;
+}
+
 /*
  * Give a range error for cache space constraints
  * - can be tail-called
-- 
2.27.0