[libgpiod][PATCH v2 2/2] core: fix reading subset of available events

[Kent Gibson <warthog618@xxxxxxxxx>]

Only read the requested number of events from the kernel rather than
reading up to 16 and quietly discarding any surplus.

The previous behavour is particularly bad for reading single events as
userspace must read the events as quickly as they arrive, effectively
negating the presence of the kernel event kfifo.

Fixes: 44921ecc9a00 (core: provide functions for reading multiple
line events at once)

Signed-off-by: Kent Gibson <warthog618@xxxxxxxxx>
---
 lib/core.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/core.c b/lib/core.c
index ad76051..b964272 100644
--- a/lib/core.c
+++ b/lib/core.c
@@ -1090,7 +1090,10 @@ int gpiod_line_event_read_fd_multiple(int fd, struct gpiod_line_event *events,
 
 	memset(evdata, 0, sizeof(evdata));
 
-	rd = read(fd, evdata, sizeof(evdata));
+	if (num_events > 16)
+		num_events = 16;
+
+	rd = read(fd, evdata, num_events * sizeof(*evdata));
 	if (rd < 0) {
 		return -1;
 	} else if ((unsigned int)rd < sizeof(*evdata)) {
-- 
2.28.0