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Re: [libvirt] [PATCH 1/2] rpc: Switch to dynamically allocated message buffer



On 04/27/2012 07:22 AM, Michal Privoznik wrote:
> Currently, we are allocating buffer for RPC messages statically.
> This is not such pain when RPC limits are small. However, if we want
> ever to increase those limits, we need to allocate buffer dynamically,
> based on RPC message len (= the first 4 bytes). Therefore we will
> decrease our mem usage in most cases and still be flexible enough in
> corner cases.
> ---
>  src/rpc/virnetclient.c       |   16 ++-
>  src/rpc/virnetmessage.c      |   12 ++-
>  src/rpc/virnetmessage.h      |    6 +-
>  src/rpc/virnetserverclient.c |   20 ++-
>  tests/virnetmessagetest.c    |  393 +++++++++++++++++++++++-------------------

Wow, the biggest impact was to the testsuite.

>  5 files changed, 264 insertions(+), 183 deletions(-)
> 
> +++ b/src/rpc/virnetmessage.h
> @@ -31,13 +31,11 @@ typedef virNetMessage *virNetMessagePtr;
>  
>  typedef void (*virNetMessageFreeCallback)(virNetMessagePtr msg, void *opaque);
>  
> -/* Never allocate this (huge) buffer on the stack. Always
> - * use virNetMessageNew() to allocate on the heap
> - */
>  struct _virNetMessage {
>      bool tracked;
>  
> -    char buffer[VIR_NET_MESSAGE_MAX + VIR_NET_MESSAGE_LEN_MAX];
> +    //char buffer[VIR_NET_MESSAGE_MAX + VIR_NET_MESSAGE_LEN_MAX];
> +    char *buffer;

Drop the C++ comment (starting with //), and instead write:

char *buffer; /* Typically VIR_NET_MESSAGE_MAX + VIR_NET_MESSAGE_LEN_MAX */

> @@ -373,6 +378,9 @@ virNetServerClientPtr virNetServerClientNew(virNetSocketPtr sock,
>      if (!(client->rx = virNetMessageNew(true)))
>          goto error;
>      client->rx->bufferLength = VIR_NET_MESSAGE_LEN_MAX;
> +    if (VIR_ALLOC_N(client->rx->buffer, client->rx->bufferLength) < 0) {
> +        virReportOOMError();
> +    }

Shouldn't this 'goto error'?

> @@ -922,6 +930,11 @@ readmore:
>                  client->wantClose = true;
>              } else {
>                  client->rx->bufferLength = VIR_NET_MESSAGE_LEN_MAX;
> +                if (VIR_ALLOC_N(client->rx->buffer,
> +                                client->rx->bufferLength) < 0) {
> +                    virReportOOMError();
> +                    client->wantClose = true;
> +                }
>                  client->nrequests++;

Do you still want nrequests incremented on failure to allocate?

Everything else looked okay.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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