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Re: [libvirt] [PATCH] qemu: Fix PCI address allocation



On 07/30/2010 08:56 AM, Jiri Denemark wrote:
> When attaching a PCI device which doesn't explicitly set its PCI
> address, libvirt allocates the address automatically. The problem is
> that when checking which PCI address is unused, we only check for those
> with slot number higher than the highest slot number ever used.
> 
> Thus attaching/detaching such device several times in a row (31 is the
> theoretical limit, less then 30 tries are enough in practise) makes any
> further device attachment fail. Furthermore, attaching a device with
> predefined PCI address to 0:0:31 immediately forbids attachment of any
> PCI device without explicit address.
> 
> This patch changes the logic so that we always check all PCI addresses
> before we say there is no PCI address available.
> ---
>  src/qemu/qemu_conf.c |   14 ++++----------
>  1 files changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
> index 57bc02f..eaebcc1 100644
> --- a/src/qemu/qemu_conf.c
> +++ b/src/qemu/qemu_conf.c
> @@ -2055,8 +2055,6 @@ qemuAssignDeviceAliases(virDomainDefPtr def, unsigned long long qemuCmdFlags)
>  #define QEMU_PCI_ADDRESS_LAST_SLOT 31
>  struct _qemuDomainPCIAddressSet {
>      virHashTablePtr used;
> -    int nextslot;
> -    /* XXX add domain, bus later when QEMU allows > 1 */

> -    for (i = addrs->nextslot ; i <= QEMU_PCI_ADDRESS_LAST_SLOT ; i++) {
> +    for (i = 0 ; i <= QEMU_PCI_ADDRESS_LAST_SLOT ; i++) {

Don't we still want to start from the last slot, and wrap around the
search only when we reach the end, rather than always starting from 0?
I'm thinking particularly about compatibility with older qemu, where
always starting from 0 risks interleaving new assignments among the
pre-assigned slots, and may end up allocating slots in a way that throws
off Windows.  Or am I worried about a non-issue?

-- 
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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