[PATCH] libxc/PM: correct (not just) error handling in xc_get_cpufreq_para()

[Jan Beulich <jbeulich@xxxxxxxx>]

>From their introduction all xc_hypercall_bounce_pre() uses, when they
failed, would properly cause exit from the function including cleanup,
yet without informing the caller of the failure. Purge the unlock_1
label for being both pointless and mis-named.

An earlier attempt to switch to the usual split between return value and
errno wasn't quite complete.

HWP work made the cleanup of the "available governors" array
conditional, neglecting the fact that the condition used may not be the
condition that was used to allocate the buffer (as the structure field
is updated upon getting back EAGAIN). Throughout the function, use the
local variable being introduced to address that.

Fixes: 4513025a8790 ("libxc: convert sysctl interfaces over to hypercall 
buffers")
Amends: 73367cf3b4b4 ("libxc: Fix xc_pm API calls to return negative error and 
stash error in errno")
Fixes: 31e264c672bc ("pmstat&xenpm: Re-arrage for cpufreq union")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/tools/libs/ctrl/xc_pm.c
+++ b/tools/libs/ctrl/xc_pm.c
@@ -212,31 +212,32 @@ int xc_get_cpufreq_para(xc_interface *xc
     DECLARE_NAMED_HYPERCALL_BOUNCE(scaling_available_governors,
                         user_para->scaling_available_governors,
                         user_para->gov_num * CPUFREQ_NAME_LEN * sizeof(char), 
XC_HYPERCALL_BUFFER_BOUNCE_BOTH);
-
-    bool has_num = user_para->cpu_num &&
-                     user_para->freq_num &&
-                     user_para->gov_num;
+    unsigned int in_gov_num = user_para->gov_num;
+    bool has_num = user_para->cpu_num && user_para->freq_num;
 
     if ( has_num )
     {
         if ( (!user_para->affected_cpus)                    ||
              (!user_para->scaling_available_frequencies)    ||
-             (user_para->gov_num && !user_para->scaling_available_governors) )
+             (in_gov_num && !user_para->scaling_available_governors) )
         {
             errno = EINVAL;
             return -1;
         }
-        if ( xc_hypercall_bounce_pre(xch, affected_cpus) )
-            goto unlock_1;
-        if ( xc_hypercall_bounce_pre(xch, scaling_available_frequencies) )
+        ret = xc_hypercall_bounce_pre(xch, affected_cpus);
+        if ( ret )
+            return ret;
+        ret = xc_hypercall_bounce_pre(xch, scaling_available_frequencies);
+        if ( ret )
             goto unlock_2;
-        if ( user_para->gov_num &&
-             xc_hypercall_bounce_pre(xch, scaling_available_governors) )
+        if ( in_gov_num )
+            ret = xc_hypercall_bounce_pre(xch, scaling_available_governors);
+        if ( ret )
             goto unlock_3;
 
         set_xen_guest_handle(sys_para->affected_cpus, affected_cpus);
         set_xen_guest_handle(sys_para->scaling_available_frequencies, 
scaling_available_frequencies);
-        if ( user_para->gov_num )
+        if ( in_gov_num )
             set_xen_guest_handle(sys_para->scaling_available_governors,
                                  scaling_available_governors);
     }
@@ -246,7 +247,7 @@ int xc_get_cpufreq_para(xc_interface *xc
     sysctl.u.pm_op.cpuid = cpuid;
     sys_para->cpu_num  = user_para->cpu_num;
     sys_para->freq_num = user_para->freq_num;
-    sys_para->gov_num  = user_para->gov_num;
+    sys_para->gov_num  = in_gov_num;
 
     ret = xc_sysctl(xch, &sysctl);
     if ( ret )
@@ -256,12 +257,11 @@ int xc_get_cpufreq_para(xc_interface *xc
             user_para->cpu_num  = sys_para->cpu_num;
             user_para->freq_num = sys_para->freq_num;
             user_para->gov_num  = sys_para->gov_num;
-            ret = -errno;
         }
 
         if ( has_num )
             goto unlock_4;
-        goto unlock_1;
+        return ret;
     }
     else
     {
@@ -298,13 +298,13 @@ int xc_get_cpufreq_para(xc_interface *xc
     }
 
 unlock_4:
-    if ( user_para->gov_num )
+    if ( in_gov_num )
         xc_hypercall_bounce_post(xch, scaling_available_governors);
 unlock_3:
     xc_hypercall_bounce_post(xch, scaling_available_frequencies);
 unlock_2:
     xc_hypercall_bounce_post(xch, affected_cpus);
-unlock_1:
+
     return ret;
 }