From 72778681704b3d41b4ffb7a9051c5eff4d4bc520 Mon Sep 17 00:00:00 2001
From: Alain Zscheile <fogti+devel@ytrizja.de>
Date: Wed, 4 Jan 2023 08:52:23 +0100
Subject: [PATCH] use flock to provide basic concurrency protection

---
 bin/main.c | 49 +++++++++++++++++++++++++++++++++++--------------
 1 file changed, 35 insertions(+), 14 deletions(-)

diff --git a/bin/main.c b/bin/main.c
index 907ff84..ee92c02 100644
--- a/bin/main.c
+++ b/bin/main.c
@@ -1,5 +1,6 @@
 #include <y16t_db.h>
 
+#include <sys/file.h>
 #include <sys/stat.h>
 #include <errno.h>
 #include <stdlib.h>
@@ -101,12 +102,6 @@ int main(int argc, const char *argv[])
 				return -1;
 			}
 
-			fd = open(dbfile, O_RDWR | O_CREAT | O_NOCTTY);
-			if(fd == -1) {
-				perror("y16t: unable to open file");
-				return -1;
-			}
-
 			if(-1 == y16t_parse_coordinate(argv[3], x, sizeof(x))) {
 				fprintf(stderr, "y16t: invalid coordinate X\n");
 				return -1;
@@ -120,6 +115,17 @@ int main(int argc, const char *argv[])
 				return -1;
 			}
 
+			fd = open(dbfile, O_RDWR | O_CREAT | O_NOCTTY);
+			if(fd == -1) {
+				perror("y16t: unable to open file");
+				return -1;
+			}
+
+			if(flock(fd, LOCK_EX) == -1) {
+				perror("y16t: unable to lock file");
+				return -1;
+			}
+
 			tmp = y16t_db_insert(fd, x, y, z);
 			if(tmp < 0) {
 				fprintf(stderr, "y16t: insert failed with %s\n", strerror(-tmp));
@@ -133,12 +139,6 @@ int main(int argc, const char *argv[])
 				return -1;
 			}
 
-			fd = open(dbfile, O_RDWR | O_NOCTTY);
-			if(fd == -1) {
-				perror("y16t: unable to open file");
-				return -1;
-			}
-
 			if(-1 == y16t_parse_coordinate(argv[3], x, sizeof(x))) {
 				fprintf(stderr, "y16t: invalid coordinate X\n");
 				return -1;
@@ -152,6 +152,17 @@ int main(int argc, const char *argv[])
 				return -1;
 			}
 
+			fd = open(dbfile, O_RDWR | O_NOCTTY);
+			if(fd == -1) {
+				perror("y16t: unable to open file");
+				return -1;
+			}
+
+			if(flock(fd, LOCK_EX) == -1) {
+				perror("y16t: unable to lock file");
+				return -1;
+			}
+
 			//tmp = y16t_db_remove(fd, x, y, z);
 			tmp = -EOPNOTSUPP;
 			if(tmp < 0) {
@@ -171,12 +182,17 @@ int main(int argc, const char *argv[])
 				return -1;
 			}
 
-			fd = open(dbfile, O_RDWR | O_NOCTTY);
+			fd = open(dbfile, O_RDONLY | O_NOCTTY);
 			if(fd == -1) {
 				perror("y16t: unable to open file");
 				return -1;
 			}
 
+			if(flock(fd, LOCK_SH) == -1) {
+				perror("y16t: unable to lock file");
+				return -1;
+			}
+
 			varname = 'y';
 			y16t_db_foreach_y(fd, x, y16t_cli_fecb, &varname);
 			break;
@@ -192,12 +208,17 @@ int main(int argc, const char *argv[])
 				return -1;
 			}
 
-			fd = open(dbfile, O_RDWR | O_NOCTTY);
+			fd = open(dbfile, O_RDONLY | O_NOCTTY);
 			if(fd == -1) {
 				perror("y16t: unable to open file");
 				return -1;
 			}
 
+			if(flock(fd, LOCK_SH) == -1) {
+				perror("y16t: unable to lock file");
+				return -1;
+			}
+
 			varname = 'x';
 			y16t_db_foreach_x(fd, y, y16t_cli_fecb, &varname);
 			break;