[libvirt] [snmp PATCH 12/20] libvirtSnmp: turn showError() into printf-like function

[Michal Privoznik]

Currently, the following pattern is used with showError:

  printf("Some error message\n");
  showError(conn);

Not only showError does not need connection pointer, those two
lines can be merged into a single one:

  showError("Some error message");

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/libvirtSnmp.c | 79 ++++++++++++++++++++++++++++++++---------------
 1 file changed, 54 insertions(+), 25 deletions(-)

diff --git a/src/libvirtSnmp.c b/src/libvirtSnmp.c
index 88f2ec6..7aa83a1 100644
--- a/src/libvirtSnmp.c
+++ b/src/libvirtSnmp.c
@@ -43,6 +43,17 @@
 #define ATTRIBUTE_UNUSED __attribute__((__unused__))
 #endif
 
+# ifndef ATTRIBUTE_FMT_PRINTF
+#  ifndef __clang__
+#   define ATTRIBUTE_FMT_PRINTF(fmtpos, argpos) \
+       __attribute__((__format__ (__gnu_printf__, fmtpos, argpos)))
+#  else
+#   define ATTRIBUTE_FMT_PRINTF(fmtpos, argpos) \
+       __attribute__((__format__ (__printf__, fmtpos, argpos)))
+#  endif
+# endif
+
+
 int verbose = 0;
 virConnectPtr conn;
 int callbackRet = -1;
@@ -76,11 +87,31 @@ stop(int sig)
 }
 
 static void
-showError(virConnectPtr conn)
+ATTRIBUTE_FMT_PRINTF(1,2)
+showError(const char *fmt, ...)
 {
-    const char *err = virGetLastErrorMessage();
+    const char *libvirtErr = virGetLastErrorMessage();
+    char ebuf[1024];
+    int rc;
+    int size = 0;
+    va_list ap;
 
-    snmp_log(LOG_ERR, "libvirt reported: \"%s\"\n", err);
+    va_start(ap, fmt);
+    rc = vsnprintf(ebuf, sizeof(ebuf), fmt, ap);
+    size += rc;
+    va_end(ap);
+
+    if (rc < 0 || size >= sizeof(ebuf))
+        return;
+
+    rc = snprintf(ebuf + size, sizeof(ebuf) - size, ": %s\n", libvirtErr);
+    size += rc;
+
+    if (rc < 0 || size >= sizeof(ebuf))
+        return;
+
+    fputs(ebuf, stderr);
+    snmp_log(LOG_ERR, "%s", ebuf);
 
     virResetLastError();
 }
@@ -95,8 +126,7 @@ insertGuest(netsnmp_container *container, virDomainPtr domain)
     unsigned char uuid[VIR_UUID_BUFLEN];
 
     if (virDomainGetInfo(domain, &info) < 0) {
-        printf("Failed to get domain info\n");
-        showError(conn);
+        showError("Failed to get domain info");
         goto error;
     }
 
@@ -108,8 +138,7 @@ insertGuest(netsnmp_container *container, virDomainPtr domain)
 
     /* set the index of the row */
     if (virDomainGetUUID(domain, uuid) < 0) {
-        printf("Failed to get domain UUID\n");
-        showError(conn);
+        showError("Failed to get domain UUID");
         goto error;
     }
 
@@ -122,8 +151,7 @@ insertGuest(netsnmp_container *container, virDomainPtr domain)
 
     /* set the data */
     if (!(name = virDomainGetName(domain))) {
-        printf("Failed to get domain name\n");
-        showError(conn);
+        showError("Failed to get domain name");
         goto error;
     }
 
@@ -167,8 +195,7 @@ libvirtSnmpLoadGuests(netsnmp_container *container)
     virDomainPtr *domains = NULL;
 
     if ((ndomains = virConnectListAllDomains(conn, &domains, 0)) < 0) {
-        printf("Failed to list all domains\n");
-        showError(conn);
+        showError("Failed to list all domains");
         goto cleanup;
     }
 
@@ -194,7 +221,7 @@ pollingThreadFunc(void *foo)
 {
     while (run) {
         if (virEventRunDefaultImpl() < 0) {
-            showError(conn);
+            showError("Failed to run event loop");
             pthread_exit(NULL);
         }
     }
@@ -222,8 +249,10 @@ libvirtRegisterEvents(virConnectPtr conn) {
                                                    (domainEventCallback),
                                                    NULL, myFreeFunc);
 
-    if (callbackRet == -1)
-        return -1;
+    if (callbackRet == -1) {
+        showError("Failed to register libvirt event handler");
+        goto cleanup;
+    }
 
     /* we need a thread to poll for events */
     if (pthread_create(&poll_thread, NULL, pollingThreadFunc, NULL))
@@ -258,8 +287,7 @@ int libvirtSnmpInit(void)
     /* TODO: configure the URI */
     /* Use libvirt env variable LIBVIRT_DEFAULT_URI by default*/
     if (!(conn = virConnectOpenAuth(NULL, virConnectAuthPtrDefault, 0))) {
-        printf("No connection to hypervisor\n");
-        showError(conn);
+        showError("No connection to hypervisor");
         return -1;
     }
 
@@ -298,9 +326,8 @@ void libvirtSnmpShutdown(void)
     }
 
     if ((rc = virConnectClose(conn))) {
-        printf("Failed to disconnect from hypervisor. "
-               "Leaked references: %d\n", rc);
-        showError(conn);
+        showError("Failed to disconnect from hypervisor. "
+                  "Leaked references: %d\n", rc);
     }
 }
 
@@ -339,7 +366,7 @@ libvirtSnmpCreate(unsigned char *uuid, int state)
     }
 
     if (virDomainCreateWithFlags(dom, flags) < 0) {
-        showError(conn);
+        showError("Failed to create domain: %s", virDomainGetName(dom));
         goto cleanup;
     }
 
@@ -353,6 +380,7 @@ int
 libvirtSnmpDestroy(unsigned char *uuid)
 {
     virDomainPtr dom;
+    int ret = -1;
 
     if (!(dom = virDomainLookupByUUID(conn, uuid))) {
         printf("Cannot find domain to destroy\n");
@@ -360,10 +388,12 @@ libvirtSnmpDestroy(unsigned char *uuid)
     }
 
     if (virDomainDestroy(dom) < 0) {
-        showError(conn);
-        return -1;
+        showError("Failed to destroy domain %s", virDomainGetName(dom));
+        goto cleanup;
     }
 
+    ret = 0;
+ cleanup:
     virDomainFree(dom);
     return 0;
 }
@@ -374,8 +404,7 @@ libvirtSnmpChangeState(unsigned char *uuid, int newstate, int oldstate)
     virDomainPtr dom;
     int ret = -1;
 
-    dom = virDomainLookupByUUID(conn, uuid);
-    if (dom == NULL) {
+    if (!(dom = virDomainLookupByUUID(conn, uuid))) {
         printf("Cannot find domain to change\n");
         return 1;
     }
@@ -392,7 +421,7 @@ libvirtSnmpChangeState(unsigned char *uuid, int newstate, int oldstate)
     }
 
     if (ret < 0)
-        showError(conn);
+        showError("Failed to change state of %s", virDomainGetName(dom));
  out:
     virDomainFree(dom);
     return ret;
-- 
2.18.1