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Re: [libvirt] RFE: virConnectListAllDomains()



On 05/19/2012 01:52 AM, Eric Blake wrote:
Use of virConnectListDomains() and virConnectListDefinedDomains() is:

1. inherently racy.  A domain can change between active and inactive
between two back-to-back calls, and thus be entirely skipped or
enumerated twice when concatenating lists.

2. painful to use.  ListDomains gives ids, ListDefinedDomains gives
names, and the user must then call virDomainLookupByID() and
virDomainLookupByName() to convert into UUIDs.

3. requires pre-allocation.  The user must call virConnectNumOfDomains()
then over-allocate before calling virConnectListDomains(), in order to
guarantee that the list size didn't change between the two calls.

This is a proposal for a new API that addresses all three points - by
returning virDomainPtr rather than id or strings, the UUID of each
domain can be grabbed in one shot.  By consolidating things into a
single API call, there is no race in trying to piece together the
complete list.  By having libvirt allocate the resulting array, rather
than making the caller pre-allocate, the user doesn't have to worry
about a race between getting a count and using that count.  It also
provides the convenience of returning smaller lists based on various
filtering groups.

Thoughts before I expand this API and add the actual implementation?

I definitely agree with all of your points. I had very similar ideas how to implement such a functionality that actualy resulted in a very similar functionality that I've got almost ready and implemented (I was struggling with python bindings for this as I didn't notice that some of the code for looking up domains was automaticaly generated). Therefore I'd be glad if you would comment on my implementation and save work yourself :)


diff --git i/include/libvirt/libvirt.h.in w/include/libvirt/libvirt.h.in
index a817db8..ea63d9f 100644
--- i/include/libvirt/libvirt.h.in
+++ w/include/libvirt/libvirt.h.in
@@ -1192,6 +1192,38 @@ int                     virConnectListDomains
(virConnectPtr conn,
   */
  int                     virConnectNumOfDomains  (virConnectPtr conn);

+/**
+ * virConnectListAllDomainsFlags:
+ *
+ * Flags used to tune which domains are listed by
virConnectListAllDomains().
+ * Note that these flags come in groups; if all bits from a group are 0,
+ * then that group is not used to filter results.
+ */
+typedef enum {
+    VIR_CONNECT_LIST_DOMAINS_ACTIVE         = 1<<  0,
+    VIR_CONNECT_LIST_DOMAINS_INACTIVE       = 1<<  1,
+
+    VIR_CONNECT_LIST_DOMAINS_PERSISTENT     = 1<<  2,
+    VIR_CONNECT_LIST_DOMAINS_TRANSIENT      = 1<<  3,
+
+    VIR_CONNECT_LIST_DOMAINS_RUNNING        = 1<<  4,
+    VIR_CONNECT_LIST_DOMAINS_PAUSED         = 1<<  5,
+    VIR_CONNECT_LIST_DOMAINS_SHUTOFF        = 1<<  6,
+    VIR_CONNECT_LIST_DOMAINS_OTHER          = 1<<  7,
+
+    VIR_CONNECT_LIST_DOMAINS_MANAGEDSAVE    = 1<<  8,
+    VIR_CONNECT_LIST_DOMAINS_NO_MANAGEDSAVE = 1<<  9,
+
+    VIR_CONNECT_LIST_DOMAINS_AUTOSTART      = 1<<  10,
+    VIR_CONNECT_LIST_DOMAINS_NO_AUTOSTART   = 1<<  11,
+
+    VIR_CONNECT_LIST_DOMAINS_HAS_SNAPSHOT   = 1<<  12,
+    VIR_CONNECT_LIST_DOMAINS_NO_SNAPSHOT    = 1<<  13,
+} virConnectListAllDomainsFlags;

This collection of filters is impressive, I'll add them as a followup or in v2 as v1 is almost ready.

+
+int                     virConnectListAllDomains(virConnectPtr conn,
+                                                 virDomainPtr *doms,
+                                                 unsigned int flags);

My take of implementing this was basicaly identical (even the function name). The only thing i took differently was adding a parameter "ndomains" to enable limiting of size of the returned array. I don't think that this will be widely used, but it might be useful to get some of the guests if the complete list exceeds RPC limit. Do you think I should keep it?

Peter


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