Add procfs CPU usage data gathering implementation

Closes castvoid#8

CMakeLists.txt

@@ -18,6 +18,8 @@ if(FAKE)
     list(APPEND SOURCE_FILES cpu_usage_random.c)
 elseif(HAVE_MACH_MACH_HOST_H)
     list(APPEND SOURCE_FILES cpu_usage_mach.c)
+elseif(EXISTS "/proc/stat")
+    list(APPEND SOURCE_FILES cpu_usage_procfs.c)
 else()
     message(FATAL_ERROR "Don't know how to get CPU usage data on this system (you could use -DFAKE=ON)")
 endif()

README.md

@@ -19,3 +19,32 @@ cmake . && make
 ```bash
 ./hwmond
 ```
+
+### Running on Linux
+On modern Linux systems that use udev, the front panel might be attached read-only:
+
+```
+libusb: error [_get_usbfs_fd] libusb couldn't open USB device /dev/bus/usb/002/004: Permission denied
+libusb: error [_get_usbfs_fd] libusb requires write access to USB device nodes.
+Couldn't connect to front panel! (Are you running this on an Intel Xserve?)
+```
+
+To fix this, copy the provided rules file into rules.d directory:
+
+```bash
+sudo cp udev/98-apple-xserve-frontpanel.rules /lib/udev/rules.d/
+```
+
+Then reload the udev rules:
+
+```bash
+sudo udevadm control --reload-rules
+```
+
+And tell udev to trigger the rule for the front panel:
+
+```bash
+sudo udevadm trigger --attr-match=idVendor=05ac --attr-match=idProduct=8261
+```
+
+On subsequent system startups, the rule will be triggered automatically.

cpu_usage_procfs.c

@@ -0,0 +1,87 @@
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/sysinfo.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+int get_num_packages(void) {
+    FILE *fp;
+    char buf[8];
+    int last_package_id, num_packages = 0;
+    bool found_one = false;
+
+    if ((fp = popen("lscpu -p=SOCKET", "r")) == NULL) {
+        printf("ERROR opening lscpu pipe: %s\n", strerror(errno));
+        return -1;
+    }
+
+    while (fgets(buf, sizeof(buf), fp) != NULL) {
+        if (sscanf(buf, "%d", &last_package_id) == 1) {
+            found_one = true;
+        }
+    }
+
+    if (found_one) {
+        num_packages = last_package_id + 1;
+    }
+
+    if (pclose(fp))  {
+        printf("ERROR running lscpu: %s\n", strerror(errno));
+        return -1;
+    }
+
+    if (num_packages <= 0) {
+        printf("WARNING: lscpu gave invalid number of packages %d, using 1\n", num_packages);
+        num_packages = 1;
+    }
+
+    return num_packages;
+}
+
+int fetch_ticks_by_core(unsigned int **ticks_by_core_busy_ptr, unsigned int **ticks_by_core_total_ptr, unsigned int *num_cores_ptr) {
+    int num_cores = get_nprocs_conf();
+    FILE *fp;
+    char buf[100];
+    unsigned long user, nice, system, idle, busy;
+    size_t core;
+
+    // Aggregate per-core ticks into busy & total counts
+    unsigned int *ticks_by_core_busy = calloc(num_cores, sizeof(unsigned int));
+    unsigned int *ticks_by_core_total = calloc(num_cores, sizeof(unsigned int));
+
+    if (ticks_by_core_busy == NULL || ticks_by_core_total == NULL) {
+        printf("Failed to alloc\n");
+        return -1;
+    }
+
+    if ((fp = fopen("/proc/stat", "r")) == NULL) {
+        printf("ERROR opening /proc/stat: %s\n", strerror(errno));
+        return -1;
+    }
+
+    core = 0;
+    while (core < num_cores && fgets(buf, sizeof(buf), fp) != NULL) {
+        if (buf[0] == 'c' && buf[1] == 'p' && buf[2] == 'u' && buf[3] >= '0' && buf[3] <= '9') {
+            if (sscanf(buf, "%*s %ld %ld %ld %ld", &user, &nice, &system, &idle) == 4) {
+                ticks_by_core_busy[core] = busy = user + nice + system;
+                ticks_by_core_total[core] = busy + idle;
+                core++;
+            }
+        }
+    }
+
+    if (fclose(fp)) {
+        printf("ERROR closing /proc/stat: %s\n", strerror(errno));
+        return -1;
+    }
+
+    // Output aggregated data
+    *ticks_by_core_busy_ptr = ticks_by_core_busy;
+    *ticks_by_core_total_ptr = ticks_by_core_total;
+    *num_cores_ptr = num_cores;
+
+    return 0;
+}

udev/98-apple-xserve-frontpanel.rules

@@ -0,0 +1,2 @@
+# Apple Intel Xserve front panel controller
+SUBSYSTEM=="usb", ATTR{idVendor}=="05ac", ATTR{idProduct}=="8261", MODE="666"