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WDCIronportException: Internal
From:   Alistair Francis <alistair.francis@opensource.wdc.com>
To:     linux-kernel@vger.kernel.org
Cc:     jolsa@redhat.com, mingo@redhat.com, dave@stgolabs.net,
        linux-perf-users@vger.kernel.org, arnd@arndb.de,
        namhyung@kernel.org, alistair23@gmail.com, mark.rutland@arm.com,
        tglx@linutronix.de, acme@kernel.org,
        alexander.shishkin@linux.intel.com, peterz@infradead.org,
        dvhart@infradead.org, Alistair Francis <alistair.francis@wdc.com>
Subject: [PATCH v4 5/6] uapi: futex: Add a futex waitv syscall
Date:   Thu,  2 Dec 2021 21:16:58 +1000
Message-Id: <20211202111659.2077911-5-alistair.francis@opensource.wdc.com>
In-Reply-To: <20211202111659.2077911-1-alistair.francis@opensource.wdc.com>
References: <20211202111659.2077911-1-alistair.francis@opensource.wdc.com>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

From: Alistair Francis <alistair.francis@wdc.com>

This commit adds a futex waitv syscall wrapper that is exposed to
userspace.

Neither the kernel or glibc currently expose a futex wrapper, so
userspace is left performing raw syscalls. As the futex_waitv syscall
always expects a 64-bit time_t this can be tricky for 32-bit systems to
get correct.

In order to avoid userspace incorrectly passing the wrong timeouts let's
expose a public helper function that ensures the kernel is passed the
correct timeout struct.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
---
 include/uapi/linux/futex_syscall.h | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/include/uapi/linux/futex_syscall.h b/include/uapi/linux/fute=
x_syscall.h
index bac621eb319c..f637f05a3be0 100644
--- a/include/uapi/linux/futex_syscall.h
+++ b/include/uapi/linux/futex_syscall.h
@@ -89,4 +89,31 @@ __kernel_futex_syscall_nr_requeue(volatile uint32_t *u=
addr, int op, uint32_t val
 	return -1;
 }
=20
+/**
+ * __kernel_futex_syscall_waitv - Wait at multiple futexes, wake on any
+ * @waiters:    Array of waiters
+ * @nr_waiters: Length of waiters array
+ * @flags: Operation flags
+ * @timo:  Optional timeout for operation
+ */
+static inline int
+__kernel_futex_syscall_waitv(volatile struct futex_waitv *waiters, unsig=
ned long nr_waiters,
+			      unsigned long flags, struct timespec *timo, clockid_t clockid)
+{
+	/* futex_waitv expects a 64-bit time_t */
+	if (sizeof(*timo) =3D=3D sizeof(struct __kernel_timespec))
+		return syscall(__NR_futex_waitv, waiters, nr_waiters, flags, timo, clo=
ckid);
+
+	/* If the caller supplied a 32-bit time_t, convert it to 64-bit */
+	if (timo) {
+		struct __kernel_timespec ts_new;
+
+		ts_new.tv_sec =3D timo->tv_sec;
+		ts_new.tv_nsec =3D timo->tv_nsec;
+
+		return syscall(__NR_futex_waitv, waiters, nr_waiters, flags, &ts_new, =
clockid);
+	} else
+		return syscall(__NR_futex_waitv, waiters, nr_waiters, flags, NULL, clo=
ckid);
+}
+
 #endif /* _UAPI_LINUX_FUTEX_SYSCALL_H */
--=20
2.31.1