zfs_arc: Ignore the first two lines of the statistics file on Linux.

The first two lines of the statistics file on Linux contain information about
the rest of the file. They do not contain any usable statistics.
See module/spl/spl-kstat.c of the spl module of ZFS on Linux for more
information.

diff --git a/src/zfs_arc.c b/src/zfs_arc.c
index af5130a..2f8b2f4 100644 (file)
--- a/src/zfs_arc.c
+++ b/src/zfs_arc.c
@@ -212,6 +212,21 @@ static int za_read(void) {
     return (-1);
   }
 
+  // Ignore the first two lines because they contain information about
+  // the rest of the file.
+  // See kstat_seq_show_headers module/spl/spl-kstat.c of the spl kernel
+  // module.
+  if (fgets(buffer, sizeof(buffer), fh) == NULL) {
+    ERROR("zfs_arc plugin: \"%s\" does not contain a single line.", ZOL_ARCSTATS_FILE);
+    fclose(fh);
+    return (-1);
+  }
+  if (fgets(buffer, sizeof(buffer), fh) == NULL) {
+    ERROR("zfs_arc plugin: \"%s\" does not contain at least two lines.", ZOL_ARCSTATS_FILE);
+    fclose(fh);
+    return (-1);
+  }
+
   while (fgets(buffer, sizeof(buffer), fh) != NULL) {
     char *fields[3];
     value_t v;