Most of our completers used the pattern:
if ((nITEM = virITEMListAll()) < 0)
    return NULL;

but the virDomainSnapshot and virStorageVolume completers were instead
using goto error because of a prior allocation. If the ListAll fails
with -1, the cleanup label was running a loop of 'size_t i < int
nITEM', which is an extreme waste of CPU cycles.

Reported-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---

This one is a bug fix, so worth having in 5.2.

 tools/virsh-completer.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/virsh-completer.c b/tools/virsh-completer.c
index c4adbb70d0..e9ef9b99f9 100644
--- a/tools/virsh-completer.c
+++ b/tools/virsh-completer.c
@@ -278,6 +278,7 @@ virshStorageVolNameCompleter(vshControl *ctl,
     virshControlPtr priv = ctl->privData;
     virStoragePoolPtr pool = NULL;
     virStorageVolPtr *vols = NULL;
+    int rc;
     int nvols = 0;
     size_t i = 0;
     char **ret = NULL;
@@ -290,8 +291,9 @@ virshStorageVolNameCompleter(vshControl *ctl,
     if (!(pool = virshCommandOptPool(ctl, cmd, "pool", NULL)))
         return NULL;

-    if ((nvols = virStoragePoolListAllVolumes(pool, &vols, flags)) < 0)
+    if ((rc = virStoragePoolListAllVolumes(pool, &vols, flags)) < 0)
         goto error;
+    nvols = rc;

     if (VIR_ALLOC_N(ret, nvols + 1) < 0)
         goto error;
@@ -631,6 +633,7 @@ virshSnapshotNameCompleter(vshControl *ctl,
     virshControlPtr priv = ctl->privData;
     virDomainPtr dom = NULL;
     virDomainSnapshotPtr *snapshots = NULL;
+    int rc;
     int nsnapshots = 0;
     size_t i = 0;
     char **ret = NULL;
@@ -643,8 +646,9 @@ virshSnapshotNameCompleter(vshControl *ctl,
     if (!(dom = virshCommandOptDomain(ctl, cmd, NULL)))
         return NULL;

-    if ((nsnapshots = virDomainListAllSnapshots(dom, &snapshots, flags)) < 0)
+    if ((rc = virDomainListAllSnapshots(dom, &snapshots, flags)) < 0)
         goto error;
+    nsnapshots = rc;

     if (VIR_ALLOC_N(ret, nsnapshots + 1) < 0)
         goto error;
-- 
2.20.1

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On Wed, Mar 27, 2019 at 09:20:58PM -0500, Eric Blake wrote:
>Most of our completers used the pattern:
>if ((nITEM = virITEMListAll()) < 0)
>    return NULL;
>
>but the virDomainSnapshot and virStorageVolume completers were instead
>using goto error because of a prior allocation. If the ListAll fails
>with -1, the cleanup label was running a loop of 'size_t i < int
>nITEM', which is an extreme waste of CPU cycles.
>
>Reported-by: Ján Tomko <jtomko@redhat.com>
>Signed-off-by: Eric Blake <eblake@redhat.com>
>---
>
>This one is a bug fix, so worth having in 5.2.
>
> tools/virsh-completer.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>

Reviewed-by: Ján Tomko <jtomko@redhat.com>

Jano
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