[libvirt] Storage pool support for large scale deployments

[Jesse J. Cook]

I am using libvirt for large scale deployment of virtual machines.  I ran into
an issue where virConnectListStoragePools and virConnectListDefinedStoragePools
return an error if there are more than 256 pools. The following patch increases
this limitation.  Currently, I am only using in the neighborhood of 500 pools,
but this is likely to grow into the tens of thousands.

This patch did not cause any test failures.  I wrote some test code to verify
the fix worked.  The test code and the results follow.

TEST CODE:
/* pool-test src code */

#include <libvirt.h>
#include <stdlib.h>
#include <stdio.h>

static int get_active_pools(virConnectPtr vir_conn)
{
    int    ret_code  = -1;
    int    rc        = -1;
    int    num_pools = -1;
    char** pools     = NULL;

    printf("Before virConnectNumOfStoragePools\n");
    num_pools = virConnectNumOfStoragePools(vir_conn);
    printf("After virConnectNumOfStoragePools\n");
    if(0 >= num_pools) goto cleanup;

    pools = malloc(sizeof(*pools) * num_pools);
    printf("Before virConnectListStoragePools\n");
    rc    = virConnectListStoragePools(vir_conn, pools, num_pools);
    printf("After virConnectListStoragePools\n");
    if(-1 == rc) goto cleanup;

    for(int i = 0; i < num_pools; ++i) {
        if(NULL != pools[i]) free(pools[i]);
    }

    ret_code = num_pools;

cleanup:
    if(NULL != pools) free(pools);
    return ret_code;
}

static int get_inactive_pools(virConnectPtr vir_conn)
{
    int    ret_code   = -1;
    int    rc         = -1;
    int    num_pools  = -1;
    char** pools      = NULL;

    printf("Before virConnectNumOfDefinedStoragePools\n");
    num_pools = virConnectNumOfDefinedStoragePools(vir_conn);
    printf("After virConnectNumOfDefinedStoragePools\n");
    if(0 >= num_pools) goto cleanup;

    pools = malloc(sizeof(*pools) * num_pools);
    printf("Before virConnectListDefinedStoragePools\n");
    rc    = virConnectListDefinedStoragePools(vir_conn, pools, num_pools);
    printf("After virConnectListDefinedStoragePools\n");
    if(-1 == rc) goto cleanup;

    for(int i = 0; i < num_pools; ++i) {
        if(NULL != pools[i]) free(pools[i]);
    }

    ret_code = num_pools;

cleanup:
    if(NULL != pools) free(pools);
    return ret_code;
}

int main(int argc, char** argv)
{
    virConnectPtr conn = virConnectOpen("qemu:///system");

    printf("Active: %d\n"  , get_active_pools(conn  ));
    printf("Inactive: %d\n", get_inactive_pools(conn));

    virConnectClose(conn);

    return 0;
}

TEST RESULTS PRE-PATCH:
# for i in `ls -1 /etc/libvirt/storage/*`; do virsh pool-start $(basename $i .xml); done &>/dev/null
# ~/pool-test 
Before virConnectNumOfStoragePools
After virConnectNumOfStoragePools
Before virConnectListStoragePools
libvir: Remote error : too many remote undefineds: 407 > 256
After virConnectListStoragePools
Active: -1
Before virConnectNumOfDefinedStoragePools
After virConnectNumOfDefinedStoragePools
Inactive: -1
# for i in `ls -1 /etc/libvirt/storage/*`; do virsh pool-destroy $(basename $i .xml); done &>/dev/null
# ~/pool-test 
Before virConnectNumOfStoragePools
After virConnectNumOfStoragePools
Active: -1
Before virConnectNumOfDefinedStoragePools
After virConnectNumOfDefinedStoragePools
Before virConnectListDefinedStoragePools
libvir: Remote error : too many remote undefineds: 407 > 256
After virConnectListDefinedStoragePools
Inactive: -1

TEST RESULTS POST-PATCH:
# for i in `ls -1 /etc/libvirt/storage/*`; do virsh pool-start $(basename $i .xml); done &>/dev/null
# ~/pool-test 
Before virConnectNumOfStoragePools
After virConnectNumOfStoragePools
Before virConnectListStoragePools
After virConnectListStoragePools
Active: 407
Before virConnectNumOfDefinedStoragePools
After virConnectNumOfDefinedStoragePools
Inactive: -1
# for i in `ls -1 /etc/libvirt/storage/*`; do virsh pool-destroy $(basename $i .xml); done &>/dev/null
# ~/pool-test 
Before virConnectNumOfStoragePools
After virConnectNumOfStoragePools
Active: -1
Before virConnectNumOfDefinedStoragePools
After virConnectNumOfDefinedStoragePools
Before virConnectListDefinedStoragePools
After virConnectListDefinedStoragePools
Inactive: 407