tools/hv: terminate fcopy daemon if read from uio fails

Terminate endless loop in reading fails, to avoid flooding syslog.

This happens if the state of "Guest services" integration service
is changed from "enabled" to "disabled" at runtime in the VM
settings. In this case pread returns EIO.

Also handle an interrupted system call, and continue in this case.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Reviewed-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Link: https://lore.kernel.org/r/20241105081437.15689-1-olaf@aepfle.de
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20241105081437.15689-1-olaf@aepfle.de>

Author: olafhering

tools/hv/hv_fcopy_uio_daemon.c

@@ -466,8 +466,10 @@ int main(int argc, char *argv[])
 		 */
 		ret = pread(fcopy_fd, &tmp, sizeof(int), 0);
 		if (ret < 0) {
+			if (errno == EINTR || errno == EAGAIN)
+				continue;
 			syslog(LOG_ERR, "pread failed: %s", strerror(errno));
-			continue;
+			goto close;
 		}
 
 		len = HV_RING_SIZE;