Format error messages properly

Make use of strerror(errno) and format all errors equally:
function ['parameters']: error message

components/battery.c

@@ -1,5 +1,7 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <stdio.h>
+#include <string.h>
 #if defined(__linux__)
 #include <limits.h>
 #include <string.h>
@@ -28,12 +30,12 @@ battery_perc(const char *bat)
 
 	fd = open("/dev/apm", O_RDONLY);
 	if (fd < 0) {
-		fprintf(stderr, "Failed to open file /dev/apm");
+		fprintf(stderr, "open '/dev/apm': %s\n", strerror(errno));
 		return NULL;
 	}
 
 	if (ioctl(fd, APM_IOC_GETPOWER, &apm_info) < 0) {
-		fprintf(stderr, "Failed to get battery info");
+		fprintf(stderr, "ioctl 'APM_IOC_GETPOWER': %s\n", strerror(errno));
 		close(fd);
 		return NULL;
 	}

components/disk.c

@@ -1,5 +1,7 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/statvfs.h>
 
 #include "../util.h"
@@ -10,7 +12,7 @@ disk_free(const char *mnt)
 	struct statvfs fs;
 
 	if (statvfs(mnt, &fs) < 0) {
-		fprintf(stderr, "Failed to get filesystem info");
+		fprintf(stderr, "statvfs '%s': %s\n", mnt, strerror(errno));
 		return NULL;
 	}
 
@@ -24,7 +26,7 @@ disk_perc(const char *mnt)
 	struct statvfs fs;
 
 	if (statvfs(mnt, &fs) < 0) {
-		fprintf(stderr, "Failed to get filesystem info");
+		fprintf(stderr, "statvfs '%s': %s\n", mnt, strerror(errno));
 		return NULL;
 	}
 
@@ -39,7 +41,7 @@ disk_total(const char *mnt)
 	struct statvfs fs;
 
 	if (statvfs(mnt, &fs) < 0) {
-		fprintf(stderr, "Failed to get filesystem info");
+		fprintf(stderr, "statvfs '%s': %s\n", mnt, strerror(errno));
 		return NULL;
 	}
 
@@ -52,7 +54,7 @@ disk_used(const char *mnt)
 	struct statvfs fs;
 
 	if (statvfs(mnt, &fs) < 0) {
-		fprintf(stderr, "Failed to get filesystem info");
+		fprintf(stderr, "statvfs '%s': %s\n", mnt, strerror(errno));
 		return NULL;
 	}
 

components/hostname.c

@@ -1,5 +1,7 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <stdio.h>
+#include <string.h>
 #include <unistd.h>
 
 #include "../util.h"
@@ -8,7 +10,7 @@ const char *
 hostname(void)
 {
 	if (gethostname(buf, sizeof(buf)) == -1) {
-		fprintf(stderr, "gethostbyname failed");
+		fprintf(stderr, "gethostbyname: %s\n", strerror(errno));
 		return NULL;
 	}
 

components/ip.c

@@ -1,5 +1,6 @@
 /* See LICENSE file for copyright and license details. */
 #if defined(__linux__)
+#include <errno.h>
 #include <ifaddrs.h>
 #include <netdb.h>
 #include <stdio.h>
@@ -15,7 +16,7 @@ ipv4(const char *iface)
 	char host[NI_MAXHOST];
 
 	if (getifaddrs(&ifaddr) == -1) {
-		fprintf(stderr, "Failed to get IPv4 address for interface %s", iface);
+		fprintf(stderr, "getifaddrs: %s\n", strerror(errno));
 		return NULL;
 	}
 
@@ -26,7 +27,7 @@ ipv4(const char *iface)
 		s = getnameinfo(ifa->ifa_addr, sizeof(struct sockaddr_in), host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
 		if ((strcmp(ifa->ifa_name, iface) == 0) && (ifa->ifa_addr->sa_family == AF_INET)) {
 			if (s != 0) {
-				fprintf(stderr, "Failed to get IPv4 address for interface %s", iface);
+				fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s));
 				return NULL;
 			}
 			return bprintf("%s", host);
@@ -46,7 +47,7 @@ ipv6(const char *iface)
 	char host[NI_MAXHOST];
 
 	if (getifaddrs(&ifaddr) == -1) {
-		fprintf(stderr, "Failed to get IPv6 address for interface %s", iface);
+		fprintf(stderr, "getifaddrs: %s\n", strerror(errno));
 		return NULL;
 	}
 
@@ -57,7 +58,7 @@ ipv6(const char *iface)
 		s = getnameinfo(ifa->ifa_addr, sizeof(struct sockaddr_in6), host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
 		if ((strcmp(ifa->ifa_name, iface) == 0) && (ifa->ifa_addr->sa_family == AF_INET6)) {
 			if (s != 0) {
-				fprintf(stderr, "Failed to get IPv6 address for interface %s", iface);
+				fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s));
 				return NULL;
 			}
 			return bprintf("%s", host);

components/kernel_release.c

@@ -1,6 +1,8 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <sys/utsname.h>
 #include <stdio.h>
+#include <string.h>
 
 #include "../util.h"
 
@@ -10,6 +12,7 @@ kernel_release(void)
 	struct utsname udata;
 
 	if (uname(&udata) < 0) {
+		fprintf(stderr, "uname: %s\n", strerror(errno));
 		return NULL;
 	}
 

components/keyboard_indicators.c

@@ -11,7 +11,7 @@ keyboard_indicators(void)
 	XKeyboardState state;
 
 	if (dpy == NULL) {
-		fprintf(stderr, "Cannot open display");
+		fprintf(stderr, "Cannot open display\n");
 		return NULL;
 	}
 	XGetKeyboardControl(dpy, &state);

components/load_avg.c

@@ -10,7 +10,7 @@ load_avg(const char *fmt)
 	double avgs[3];
 
 	if (getloadavg(avgs, 3) < 0) {
-		fprintf(stderr, "Failed to get the load avg");
+		fprintf(stderr, "getloadavg: Could not obtain load average.\n");
 		return NULL;
 	}
 

components/num_files.c

@@ -1,4 +1,5 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <dirent.h>
 #include <stdio.h>
 #include <string.h>
@@ -13,7 +14,7 @@ num_files(const char *dir)
 	int num = 0;
 
 	if ((fd = opendir(dir)) == NULL) {
-		fprintf(stderr, "Failed to get number of files in directory %s", dir);
+		fprintf(stderr, "opendir '%s': %s\n", dir, strerror(errno));
 		return NULL;
 	}
 

components/run_command.c

@@ -1,4 +1,5 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -12,7 +13,7 @@ run_command(const char *cmd)
 
 	fp = popen(cmd, "r");
 	if (fp == NULL) {
-		fprintf(stderr, "Failed to get command output for %s", cmd);
+		fprintf(stderr, "popen '%s': %s\n", cmd, strerror(errno));
 		return NULL;
 	}
 	p = fgets(buf, sizeof(buf) - 1, fp);

components/swap.c

@@ -1,5 +1,6 @@
 /* See LICENSE file for copyright and license details. */
 #if defined(__linux__)
+#include <errno.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -15,12 +16,12 @@ swap_free(void)
 
 	fp = fopen("/proc/meminfo", "r");
 	if (fp == NULL) {
-		fprintf(stderr, "Failed to open file /proc/meminfo");
+		fprintf(stderr, "fopen '/proc/meminfo': %s\n", strerror(errno));
 		return NULL;
 	}
 
 	if ((bytes_read = fread(buf, sizeof(char), sizeof(buf) - 1, fp)) == 0) {
-		fprintf(stderr, "swap_free: read error");
+		fprintf(stderr, "fread '/proc/meminfo': %s\n", strerror(errno));
 		fclose(fp);
 		return NULL;
 	}
@@ -47,12 +48,12 @@ swap_perc(void)
 
 	fp = fopen("/proc/meminfo", "r");
 	if (fp == NULL) {
-		fprintf(stderr, "Failed to open file /proc/meminfo");
+		fprintf(stderr, "fopen '/proc/meminfo': %s\n", strerror(errno));
 		return NULL;
 	}
 
 	if ((bytes_read = fread(buf, sizeof(char), sizeof(buf) - 1, fp)) == 0) {
-		fprintf(stderr, "swap_perc: read error");
+		fprintf(stderr, "fread '/proc/meminfo': %s\n", strerror(errno));
 		fclose(fp);
 		return NULL;
 	}
@@ -83,11 +84,11 @@ swap_total(void)
 
 	fp = fopen("/proc/meminfo", "r");
 	if (fp == NULL) {
-		fprintf(stderr, "Failed to open file /proc/meminfo");
+		fprintf(stderr, "fopen '/proc/meminfo': %s\n", strerror(errno));
 		return NULL;
 	}
 	if ((bytes_read = fread(buf, sizeof(char), sizeof(buf) - 1, fp)) == 0) {
-		fprintf(stderr, "swap_total: read error");
+		fprintf(stderr, "fread '/proc/meminfo': %s\n", strerror(errno));
 		fclose(fp);
 		return NULL;
 	}
@@ -110,11 +111,11 @@ swap_used(void)
 
 	fp = fopen("/proc/meminfo", "r");
 	if (fp == NULL) {
-		fprintf(stderr, "Failed to open file /proc/meminfo");
+		fprintf(stderr, "fopen '/proc/meminfo': %s\n", strerror(errno));
 		return NULL;
 	}
 	if ((bytes_read = fread(buf, sizeof(char), sizeof(buf) - 1, fp)) == 0) {
-		fprintf(stderr, "swap_used: read error");
+		fprintf(stderr, "fread '/proc/meminfo': %s\n", strerror(errno));
 		fclose(fp);
 		return NULL;
 	}

components/uptime.c

@@ -1,5 +1,7 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <stdio.h>
+#include <string.h>
 #if defined(__linux__)
 #include <sys/sysinfo.h>
 #elif defined(__OpenBSD__)
@@ -35,8 +37,10 @@ uptime(void)
 
 	if (sysctl(mib, 2, &boottime, &size, NULL, 0) != -1)
 		uptime = now - boottime.tv_sec;
-	else
+	else {
+		fprintf(stderr, "sysctl 'KERN_BOOTTIME': %s\n", strerror(errno));
 		return NULL;
+	}
 #endif
 	h = uptime / 3600;
 	m = (uptime - h * 3600) / 60;

components/user.c

@@ -1,6 +1,8 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <pwd.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/types.h>
 #include <unistd.h>
 
@@ -18,7 +20,7 @@ username(void)
 	struct passwd *pw = getpwuid(geteuid());
 
 	if (pw == NULL) {
-		fprintf(stderr, "Failed to get username");
+		fprintf(stderr, "getpwuid '%d': %s\n", geteuid(), strerror(errno));
 		return NULL;
 	}
 

components/volume.c

@@ -1,5 +1,6 @@
 /* See LICENSE file for copyright and license details. */
 #if defined(__linux__)
+#include <errno.h>
 #include <fcntl.h>
 #include <sys/soundcard.h>
 #include <sys/ioctl.h>
@@ -18,19 +19,19 @@ vol_perc(const char *card)
 
 	afd = open(card, O_RDONLY | O_NONBLOCK);
 	if (afd == -1) {
-		fprintf(stderr, "Cannot open %s", card);
+		fprintf(stderr, "open '%s': %s\n", card, strerror(errno));
 		return NULL;
 	}
 
 	if (ioctl(afd, SOUND_MIXER_READ_DEVMASK, &devmask) == -1) {
-		fprintf(stderr, "Cannot get volume for %s", card);
+		fprintf(stderr, "ioctl 'SOUND_MIXER_READ_DEVMASK': %s\n", strerror(errno));
 		close(afd);
 		return NULL;
 	}
 	for (i = 0; i < LEN(vnames); i++) {
 		if (devmask & (1 << i) && !strcmp("vol", vnames[i])) {
 			if (ioctl(afd, MIXER_READ(i), &v) == -1) {
-				fprintf(stderr, "vol_perc: ioctl");
+				fprintf(stderr, "ioctl 'MIXER_READ(%d)': %s\n", i, strerror(errno));
 				close(afd);
 				return NULL;
 			}

components/wifi.c

@@ -1,5 +1,6 @@
 /* See LICENSE file for copyright and license details. */
 #if defined(__linux__)
+#include <errno.h>
 #include <ifaddrs.h>
 #include <linux/wireless.h>
 #include <sys/socket.h>
@@ -25,7 +26,7 @@ wifi_perc(const char *iface)
 	snprintf(path, sizeof(path), "%s%s%s", "/sys/class/net/", iface, "/operstate");
 	fp = fopen(path, "r");
 	if (fp == NULL) {
-		fprintf(stderr, "Failed to open file %s", path);
+		fprintf(stderr, "fopen '%s': %s\n", path, strerror(errno));
 		return NULL;
 	}
 	p = fgets(status, 5, fp);
@@ -36,7 +37,7 @@ wifi_perc(const char *iface)
 
 	fp = fopen("/proc/net/wireless", "r");
 	if (fp == NULL) {
-		fprintf(stderr, "Failed to open file /proc/net/wireless");
+		fprintf(stderr, "fopen '/proc/net/wireless': %s\n", strerror(errno));
 		return NULL;
 	}
 
@@ -71,12 +72,12 @@ wifi_essid(const char *iface)
 	snprintf(wreq.ifr_name, sizeof(wreq.ifr_name), "%s", iface);
 
 	if (sockfd == -1) {
-		fprintf(stderr, "Failed to get ESSID for interface %s", iface);
+		fprintf(stderr, "socket 'AF_INET': %s\n", strerror(errno));
 		return NULL;
 	}
 	wreq.u.essid.pointer = id;
 	if (ioctl(sockfd,SIOCGIWESSID, &wreq) == -1) {
-		fprintf(stderr, "Failed to get ESSID for interface %s", iface);
+		fprintf(stderr, "ioctl 'SIOCGIWESSID': %s\n", strerror(errno));
 		close(sockfd);
 		return NULL;
 	}

util.c

@@ -1,4 +1,5 @@
 /* See LICENSE file for copyright and license details. */
+#include <errno.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
@@ -29,7 +30,7 @@ pscanf(const char *path, const char *fmt, ...)
 	int n;
 
 	if (!(fp = fopen(path, "r"))) {
-		fprintf(stderr, "fopen for %s failed", path);
+		fprintf(stderr, "fopen '%s': %s\n", path, strerror(errno));
 		return -1;
 	}
 	va_start(ap, fmt);