Hacked together a smart_ plugin in C

There is some trickery going on to not wakeup the disk when it's in standby

Note: this was aimed at munin-c, but was rejected since it uses a
subprocess that calls the `smartctl` tool.

plugins/disk/smart-c/smart.c

@@ -0,0 +1,201 @@
+/*
+ * Copyright (C) 2017 Bastiaan van Kesteren <bas@edeation.nl> - All rights reserved.
+ *
+ * This copyrighted material is made available to anyone wishing to use,
+ * modify, copy, or redistribute it subject to the terms and conditions
+ * of the GNU General Public License v.2 or v.3.
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <libgen.h>
+#include <sys/wait.h>
+#include "common.h"
+
+static char getitem(char *input, unsigned char item, char *output)
+{
+	unsigned char i = 0;
+	unsigned char seperators = 0;
+	char know_this_seperator = 0;
+	unsigned char start = 0;
+	unsigned char stop = 0;
+
+	/* Trim starting spaces */
+	while (input[i] == ' ') {
+		i++;
+	}
+
+	/* If we're requested to return the very first item... */
+	if (seperators == item) {
+		start = i;
+	}
+
+	while (input[i] && seperators < item + 1) {
+		if (input[i] == ' ') {
+			if (know_this_seperator == 0) {
+				know_this_seperator = 1;
+				seperators++;
+				if (seperators == item + 1) {
+					stop = i;
+					break;
+				}
+			}
+		} else if (know_this_seperator) {
+			know_this_seperator = 0;
+			if (seperators == item) {
+				start = i;
+			}
+		} else if (input[i] == '\n') {
+			input[i] = 0;
+			break;
+		}
+
+		i++;
+	}
+
+	if (stop) {
+		/* Found stop, means we have a start aswell */
+		strncpy(output, &input[start], stop - start);
+		return 1;
+	} else if (start) {
+		/* Have a start, no stop. We're returning the last item of the string */
+		strcpy(output, &input[start]);
+		return 1;
+	}
+
+	return 0;
+}
+
+int smart(int argc, char **argv)
+{
+	char command[50];
+	char output[255];
+	char label[25][100];
+	char value[25][25];
+	unsigned char attribute = 0;
+	FILE *f;
+	unsigned int i;
+
+	/* Prepare and execute command */
+	snprintf(command, sizeof(command),
+		 "smartctl -A -d ata /dev/%s -n standby",
+		 &basename(argv[0])[6]);
+	if ((f = popen(command, "r")) == 0) {
+		return fail("cannot initiate command execution");
+	}
+
+	/* Process command output */
+	while (fgets(output, sizeof(output), f) != NULL) {
+		printf("#%s", output);
+		/* Filter out attribute lines; look for lines starting with an attribute ID */
+		if ((output[0] >= '0' && output[0] <= '9') ||
+		    (output[0] == ' '
+		     && (output[1] >= '0' && output[1] <= '9'))
+		    || (output[0] == ' ' && output[1] == ' '
+			&& (output[2] >= '0' && output[2] <= '9'))) {
+			/* Now, print the 2nd column (attribute name) and the 10th (raw value) */
+
+			getitem(output, 1, label[attribute]);
+			getitem(output, 9, value[attribute]);
+			attribute++;
+			if (attribute == 25) {
+				break;
+			}
+		}
+	}
+
+	/* Close command (this is where we get the exit code! */
+	i = WEXITSTATUS(pclose(f));
+	if (i == 1 ||		/* smartctl command did not parse */
+	    /*i == 2 || *//* smartctl device open failed */
+	    i == 127) {		/* command not found */
+		return fail("command execution failed");
+	}
+
+	/* Setup for caching */
+	snprintf(command, sizeof(command), "/mnt/ram/smart_%s",
+		 &basename(argv[0])[6]);
+
+	if (attribute == 0) {
+		printf("#Cached attributes\n");
+		/* No output from command, try to fetch attribute-list from disk with NaN values */
+		if ((f = fopen(command, "r")) == 0) {
+			return
+			    fail
+			    ("command did not return data, no cached attribute-list");
+			return 0;
+		}
+	}
+
+	if (argc > 1) {
+		if (strcmp(argv[1], "config") == 0) {
+			printf
+			    ("graph_title S.M.A.R.T values for drive %s\n"
+			     "graph_args --base 1000 --lower-limit 0\n"
+			     "graph_vlabel Attribute S.M.A.R.T value\n"
+			     "graph_category disk\n",
+			     &basename(argv[0])[6]);
+
+			if (attribute == 0) {
+				while (fgets(output, sizeof(output), f) !=
+				       NULL) {
+					for (i = 0; i < strlen(output);
+					     i++) {
+						if (output[i] == '\n') {
+							output[i] = '\0';
+							break;
+						}
+					}
+					printf("%s.label %s\n", output,
+					       output);
+				}
+				fclose(f);
+			} else {
+				f = fopen(command, "w");
+				do {
+					attribute--;
+					printf("%s.label %s\n",
+					       label[attribute],
+					       label[attribute]);
+					if (f) {
+						fprintf(f, "%s\n",
+							label[attribute]);
+					}
+				} while (attribute);
+
+				if (f) {
+					fclose(f);
+				}
+			}
+			printf("standby.label standby\n");
+			return 0;
+		}
+	}
+
+	/* Asking for a fetch */
+	if (attribute == 0) {
+		/* No data, use cached info */
+		while (fgets(output, sizeof(output), f) != NULL) {
+			for (i = 0; i < strlen(output); i++) {
+				if (output[i] == '\n') {
+					output[i] = '\0';
+					break;
+				}
+			}
+			printf("%s.value U\n", output);
+		}
+		printf("standby.value 1\n");
+		fclose(f);
+	} else {
+		do {
+			attribute--;
+			printf("%s.value %s\n", label[attribute],
+			       value[attribute]);
+		} while (attribute);
+		printf("standby.value 0\n");
+	}
+
+	return 0;
+}