Re: [Qemu-devel] [PATCH v3 16/46] ivshmem: remove max_peer field

[Claudio Fontana <claudio.fontana@huawei.com>]

On 15.09.2015 18:07, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> max_peer isn't really useful, it tracks the maximum received VM id, but
> that quickly matches nb_peers, the size of the peers array. Since VM
> come and go, there might be sparse peers so it doesn't help much in
> general to have this value around.

Does this max_peer provide any value if VMs _don't_ come and go?
Not that I see any.

> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  hw/misc/ivshmem.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> index 07f2182..cda7dce 100644
> --- a/hw/misc/ivshmem.c
> +++ b/hw/misc/ivshmem.c
> @@ -90,7 +90,6 @@ typedef struct IVShmemState {
>  
>      Peer *peers;
>      int nb_peers; /* how many guests we have space for */
> -    int max_peer; /* maximum numbered peer */
>  
>      int vm_id;
>      uint32_t vectors;
> @@ -200,7 +199,7 @@ static void ivshmem_io_write(void *opaque, hwaddr addr,
>  
>          case DOORBELL:
>              /* check that dest VM ID is reasonable */
> -            if (dest > s->max_peer) {
> +            if (dest >= s->nb_peers) {
>                  IVSHMEM_DPRINTF("Invalid destination VM ID (%d)\n", dest);
>                  break;
>              }
> @@ -574,11 +573,6 @@ static void ivshmem_read(void *opaque, const uint8_t *buf, int size)
>      /* increment count for particular guest */
>      s->peers[incoming_posn].nb_eventfds++;
>  
> -    /* keep track of the maximum VM ID */
> -    if (incoming_posn > s->max_peer) {
> -        s->max_peer = incoming_posn;
> -    }
> -
>      if (incoming_posn == s->vm_id) {
>          s->eventfd_chr[guest_max_eventfd] = create_eventfd_chr_device(s,
>                     &s->peers[s->vm_id].eventfds[guest_max_eventfd],
> @@ -721,8 +715,6 @@ static void pci_ivshmem_realize(PCIDevice *dev, Error **errp)
>          PCI_BASE_ADDRESS_MEM_PREFETCH;;
>      Error *local_err = NULL;
>  
> -    s->max_peer = -1;
> -
>      if (s->sizearg == NULL) {
>          s->ivshmem_size = 4 << 20; /* 4 MB default */
>      } else {
>