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snapshot: virsh fallback for snapshot-list --descendants --from

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Given a list of snapshots and their parents, finding all descendants
requires a hairy traversal.  This code is O(n^3); it could maybe be
made to scale O(n^2) with the use of a hash table, but that costs more
memory.  Hopefully there aren't too many people with a hierarchy
so large as to approach REMOTE_DOMAIN_SNAPSHOT_LIST_NAMES_MAX (1024).

* tools/virsh.c (cmdSnapshotList): Add final fallback.
This commit is contained in:
Eric Blake 2011-09-29 16:31:02 -06:00
parent 16d7b3908e
commit 521cc44700
1 changed files with 60 additions and 7 deletions
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67
tools/virsh.c
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@ -13177,6 +13177,7 @@ cmdSnapshotList(vshControl *ctl, const vshCmd *cmd)
bool tree = vshCommandOptBool(cmd, "tree");
const char *from = NULL;
virDomainSnapshotPtr start = NULL;
int start_index = -1;
bool descendants = false;
if (vshCommandOptString(cmd, "from", &from) < 0) {
@ -13231,10 +13232,8 @@ cmdSnapshotList(vshControl *ctl, const vshCmd *cmd)
numsnaps = ctl->useSnapshotOld ? -1 :
virDomainSnapshotNumChildren(start, flags);
if (numsnaps < 0) {
/* XXX also want to emulate --descendants without --tree */
if ((!descendants || tree) &&
(ctl->useSnapshotOld ||
last_error->code == VIR_ERR_NO_SUPPORT)) {
if (ctl->useSnapshotOld ||
last_error->code == VIR_ERR_NO_SUPPORT) {
/* We can emulate --from. */
virFreeError(last_error);
last_error = NULL;
@ -13312,6 +13311,11 @@ cmdSnapshotList(vshControl *ctl, const vshCmd *cmd)
if (tree || ctl->useSnapshotOld) {
parents = vshCalloc(ctl, sizeof(char *), actual);
for (i = (from && !ctl->useSnapshotOld); i < actual; i++) {
if (ctl->useSnapshotOld && STREQ(names[i], from)) {
start_index = i;
continue;
}
/* free up memory from previous iterations of the loop */
if (snapshot)
virDomainSnapshotFree(snapshot);
@ -13345,12 +13349,61 @@ cmdSnapshotList(vshControl *ctl, const vshCmd *cmd)
goto cleanup;
} else {
if (ctl->useSnapshotOld && descendants) {
/* XXX emulate --descendants as well */
goto cleanup;
bool changed = false;
/* Make multiple passes over the list - first pass NULLs
* out all roots except start, remaining passes NULL out
* any entry whose parent is not still in list. Also, we
* NULL out parent when name is known to be in list.
* Sorry, this is O(n^3) - hope your hierarchy isn't huge. */
if (start_index < 0) {
vshError(ctl, _("snapshot %s disappeared from list"), from);
goto cleanup;
}
for (i = 0; i < actual; i++) {
if (i == start_index)
continue;
if (!parents[i]) {
VIR_FREE(names[i]);
} else if (STREQ(parents[i], from)) {
VIR_FREE(parents[i]);
changed = true;
}
}
if (!changed) {
ret = true;
goto cleanup;
}
while (changed) {
changed = false;
for (i = 0; i < actual; i++) {
bool found = false;
int j;
if (!names[i] || !parents[i])
continue;
for (j = 0; j < actual; j++) {
if (!names[j] || i == j)
continue;
if (STREQ(parents[i], names[j])) {
found = true;
if (!parents[j])
VIR_FREE(parents[i]);
break;
}
}
if (!found) {
changed = true;
VIR_FREE(names[i]);
}
}
}
VIR_FREE(names[start_index]);
}
for (i = 0; i < actual; i++) {
if (ctl->useSnapshotOld && STRNEQ_NULLABLE(parents[i], from))
if (ctl->useSnapshotOld &&
(descendants ? !names[i] : STRNEQ_NULLABLE(parents[i], from)))
continue;
/* free up memory from previous iterations of the loop */