Turbostat plugin: relax dependency on root

Backporting commit 98481e79b60a50d699b79292ff1b7e56e7fa8425
from Len Brown <len.brown@intel.com>

For turbostat to run as non-root, it needs to permissions:

1. read access to /dev/cpu/*/msr
        via standard user/group/world file permissions

2. CAP_SYS_RAWIO
        eg.  # setcap cap_sys_rawio=ep $(which collectd)

Yes, running as root still works.

diff --git a/src/turbostat.c b/src/turbostat.c
index 34c11b889f619450c73e8ac97cca96743eec3256..cd2cf434bc7d5594d2fabaf431b5014095628562 100644 (file)
--- a/src/turbostat.c
+++ b/src/turbostat.c
@@ -57,6 +57,7 @@
 #include <ctype.h>
 #include <sched.h>
 #include <cpuid.h>
+#include <sys/capability.h>
 
 #define PLUGIN_NAME "turbostat"
 
@@ -1484,6 +1485,52 @@ out:
        return ret;
 }
 
+static int
+check_permissions(void)
+{
+       struct __user_cap_header_struct cap_header_data;
+       cap_user_header_t cap_header = &cap_header_data;
+       struct __user_cap_data_struct cap_data_data;
+       cap_user_data_t cap_data = &cap_data_data;
+       int ret = 0;
+
+       if (getuid() == 0) {
+               /* We have everything we need */
+               return 0;
+       }
+
+       /* check for CAP_SYS_RAWIO */
+       cap_header->pid = getpid();
+       cap_header->version = _LINUX_CAPABILITY_VERSION;
+       if (capget(cap_header, cap_data) < 0) {
+               ERROR("Turbostat plugin: capget failed");
+               return -1;
+       }
+
+       if ((cap_data->effective & (1 << CAP_SYS_RAWIO)) == 0) {
+               WARNING("Turbostat plugin: Collectd doesn't have the "
+                       "CAP_SYS_RAWIO capability. If you don't want to run "
+                       "collectd as root, try running \"setcap "
+                       "cap_sys_rawio=ep\" on collectd binary");
+               ret = -1;
+       }
+
+       if (euidaccess("/dev/cpu/0/msr", R_OK)) {
+               WARNING("Turbostat plugin: Collectd cannot open"
+                       "/dev/cpu/0/msr. If you don't want to run collectd as "
+                       "root, you need to change the ownership (chown) and "
+                       "permissions on /dev/cpu/*/msr to allow such access");
+               ret = -1;
+       }
+
+       if (ret != 0)
+               ERROR("Turbostat plugin: Initialization failed: this plugin "
+                     "requires collectd to either to run as root or give "
+                     "collectd a special capability (CAP_SYS_RAWIO) and read "
+                      "access to /dev/cpu/*/msr (see previous warnings)");
+       return ret;
+}
+
 static int
 turbostat_init(void)
 {
@@ -1498,12 +1545,7 @@ turbostat_init(void)
                return -1;
        }
 
-       if (getuid() != 0) {
-               ERROR("Turbostat plugin: Initialization failed: this plugin "
-                     "requires collectd to run as root in order to read "
-                     "special CPU registers");
-               return -1;
-       }
+       DO_OR_GOTO_ERR(check_permissions());
 
        DO_OR_GOTO_ERR(probe_cpu());