From: Andrei Tatar <andrei@unikraft.io>
Date: Wed, 22 Jan 2025 22:26:44 +0000 (+0100)
Subject: lib/posix-timerfd: Fix counter on subsequent reads
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=8844fba3fdafa823590b56af583a2d558bcdcd24;p=unikraft%2Funikraft.git

lib/posix-timerfd: Fix counter on subsequent reads

The internal counter of a timerfd is returned on read() and reset to 0,
and should be increased by 1 for every subsequent expiration.
A logic error in the current code makes every update set the counter to
the total expirations rather than since last read, leading to subsequent
successful reads returning wrong counts.
This change fixes this error.

Signed-off-by: Andrei Tatar <andrei@unikraft.io>
Approved-by: Sergiu Moga <sergiu@unikraft.io>
Reviewed-by: Sergiu Moga <sergiu@unikraft.io>
GitHub-Closes: #1567
---

diff --git a/lib/posix-timerfd/timerfd.c b/lib/posix-timerfd/timerfd.c
index eb1614165..1e1b32719 100644
--- a/lib/posix-timerfd/timerfd.c
+++ b/lib/posix-timerfd/timerfd.c
@@ -32,6 +32,7 @@ static const char TIMERFD_VOLID[] = "timerfd_vol";
 struct timerfd_node {
 	struct itimerspec set;
 	__u64 val;
+	__u64 total;
 	clockid_t clkid;
 	struct uk_thread *upthread;
 };
@@ -102,12 +103,11 @@ static __nsec _timerfd_update(const struct uk_file *f)
 	deadline = now + st.next;
 
 	/* Update val & events */
-	if (st.exp != d->val) {
-		d->val = st.exp;
-		if (st.exp)
-			uk_file_event_set(f, UKFD_POLLIN);
-		else
-			uk_file_event_clear(f, UKFD_POLLIN);
+	UK_ASSERT(st.exp >= d->total);
+	if (st.exp > d->total) {
+		d->val += st.exp - d->total;
+		d->total = st.exp;
+		uk_file_event_set(f, UKFD_POLLIN);
 	}
 	return deadline;
 }
@@ -124,6 +124,7 @@ static void _timerfd_set(struct timerfd_node *d, const struct itimerspec *set)
 		/* Arm */
 		d->set.it_value = set->it_value;
 		d->set.it_interval = set->it_interval;
+		d->total = 0;
 		uk_thread_wake(d->upthread);
 	}
 }