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sys_linux: avoid blocking in reading of external PHC timestamp

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The kernel has a common queue for all readers of a PHC device. With
multiple PHC refclocks using the same device some reads blocked. PHC
devices don't seem to support non-blocking reads. Use poll() to check if
a timestamp is available before reading from the descriptor.
This commit is contained in:
Miroslav Lichvar 2023-03-01 14:41:34 +01:00
parent 06945d927b
commit 39ff7ceeca
1 changed files with 11 additions and 0 deletions
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11
sys_linux.c
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@ -35,6 +35,7 @@
#if defined(FEAT_PHC) || defined(HAVE_LINUX_TIMESTAMPING)
#include <linux/ptp_clock.h>
#include <poll.h>
#endif
#ifdef FEAT_SCFILTER
@ -994,6 +995,16 @@ int
SYS_Linux_ReadPHCExtTimestamp(int fd, struct timespec *phc_ts, int *channel)
{
struct ptp_extts_event extts_event;
struct pollfd pfd;
/* Make sure the read will not block in case we have multiple
descriptors of the same PHC (O_NONBLOCK does not work) */
pfd.fd = fd;
pfd.events = POLLIN;
if (poll(&pfd, 1, 0) != 1 || pfd.revents != POLLIN) {
DEBUG_LOG("Missing PHC extts event");
return 0;
}
if (read(fd, &extts_event, sizeof (extts_event)) != sizeof (extts_event)) {
DEBUG_LOG("Could not read PHC extts event");