onewire_parser: Implement simultaneous reading

[rrdd] / onewire_parser.c

diff --git a/onewire_parser.c b/onewire_parser.c
index e129e5c5e78efbcf47be588656d5abbc5af1c9bd..07d359b7c8dadf2c43035600816b2c0b5e1d1fd3 100644 (file)
--- a/onewire_parser.c
+++ b/onewire_parser.c
@@ -5,6 +5,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <math.h>
+#include <time.h>
 
 #include "parser.h"
 #include "debug.h"
@@ -189,6 +190,52 @@ out_close:
        return ret;
 }
 
+static void enable_simultaneous_reading(const char *mountpoint)
+{
+       static time_t last_simultaneous;
+       static struct mutex lock = {
+               .lock = PTHREAD_MUTEX_INITIALIZER,
+       };
+
+       time_t now = time(0);
+       int fd;
+       int ret;
+       char path[4096];
+       char one = '1';
+
+       mutex_lock(&lock);
+       /* Arbitrary 10 second limit between simultaneous reads */
+       if (now < last_simultaneous + 10) {
+               mutex_unlock(&lock);
+               return;
+       }
+
+       last_simultaneous = now;
+       mutex_unlock(&lock);
+
+       /*
+        * We only protect setting the variable. From now on we have
+        * 10 seconds time until we could race writing multiple times
+        * to this file. If that happens, well, can't help it..
+        */
+
+       strncpy(path, mountpoint, sizeof(path) - 1);
+       strncat(path, "/simultaneous/temperature", sizeof(path) - 1);
+       path[sizeof(path) - 1 ] = '\0';
+
+       fd = open(path, O_WRONLY);
+       if (path < 0) {
+               pr_err("Failed to open %s for writing: %m\n", path);
+               return;
+       }
+
+       ret = write(fd, &one, 1);
+       if (ret < 0)
+               pr_warn("Failed to write to %s: %m\n", path);
+
+       close(fd);
+}
+
 static int is_mount_point(const char *str)
 {
        /*
@@ -258,6 +305,9 @@ undefined:
 
                parse_opts(parser_data[i], ow_path, sizeof(ow_path), &offset);
 
+               if (is_mountpoint)
+                       enable_simultaneous_reading(mount_point);
+
                while (1) {
                        int j;
                        char *tmp2;