[Qemu-devel] Re: [PATCH] net: Fix send queue ordering

[Jan Kiszka <jan.kiszka@siemens.com>]

Jan Kiszka wrote:
> Ensure that packets enqueued for delayed delivery are dequeued in FIFO
> order. At least one simplistic guest TCP/IP stack became unhappy due to
> sporadically reordered packet streams.

Before I forget: This should also be considered for 0.11-rc (it's a 0.11
regression).

> 
> At this chance, switch the send queue implementation to TAILQ.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> 
>  net.c |   29 ++++++++++++-----------------
>  net.h |    5 +++--
>  2 files changed, 15 insertions(+), 19 deletions(-)
> 
> diff --git a/net.c b/net.c
> index 1b531e7..d7a1ab6 100644
> --- a/net.c
> +++ b/net.c
> @@ -436,33 +436,28 @@ qemu_deliver_packet(VLANClientState *sender, const uint8_t *buf, int size)
>  
>  void qemu_purge_queued_packets(VLANClientState *vc)
>  {
> -    VLANPacket **pp = &vc->vlan->send_queue;
> -
> -    while (*pp != NULL) {
> -        VLANPacket *packet = *pp;
> +    VLANPacket *packet, *next;
>  
> +    TAILQ_FOREACH_SAFE(packet, &vc->vlan->send_queue, entry, next) {
>          if (packet->sender == vc) {
> -            *pp = packet->next;
> +            TAILQ_REMOVE(&vc->vlan->send_queue, packet, entry);
>              qemu_free(packet);
> -        } else {
> -            pp = &packet->next;
>          }
>      }
>  }
>  
>  void qemu_flush_queued_packets(VLANClientState *vc)
>  {
> -    VLANPacket *packet;
> -
> -    while ((packet = vc->vlan->send_queue) != NULL) {
> +    while (!TAILQ_EMPTY(&vc->vlan->send_queue)) {
> +        VLANPacket *packet;
>          int ret;
>  
> -        vc->vlan->send_queue = packet->next;
> +        packet = TAILQ_FIRST(&vc->vlan->send_queue);
> +        TAILQ_REMOVE(&vc->vlan->send_queue, packet, entry);
>  
>          ret = qemu_deliver_packet(packet->sender, packet->data, packet->size);
>          if (ret == 0 && packet->sent_cb != NULL) {
> -            packet->next = vc->vlan->send_queue;
> -            vc->vlan->send_queue = packet;
> +            TAILQ_INSERT_HEAD(&vc->vlan->send_queue, packet, entry);
>              break;
>          }
>  
> @@ -480,12 +475,12 @@ static void qemu_enqueue_packet(VLANClientState *sender,
>      VLANPacket *packet;
>  
>      packet = qemu_malloc(sizeof(VLANPacket) + size);
> -    packet->next = sender->vlan->send_queue;
>      packet->sender = sender;
>      packet->size = size;
>      packet->sent_cb = sent_cb;
>      memcpy(packet->data, buf, size);
> -    sender->vlan->send_queue = packet;
> +
> +    TAILQ_INSERT_TAIL(&sender->vlan->send_queue, packet, entry);
>  }
>  
>  ssize_t qemu_send_packet_async(VLANClientState *sender,
> @@ -597,7 +592,6 @@ static ssize_t qemu_enqueue_packet_iov(VLANClientState *sender,
>      max_len = calc_iov_length(iov, iovcnt);
>  
>      packet = qemu_malloc(sizeof(VLANPacket) + max_len);
> -    packet->next = sender->vlan->send_queue;
>      packet->sender = sender;
>      packet->sent_cb = sent_cb;
>      packet->size = 0;
> @@ -609,7 +603,7 @@ static ssize_t qemu_enqueue_packet_iov(VLANClientState *sender,
>          packet->size += len;
>      }
>  
> -    sender->vlan->send_queue = packet;
> +    TAILQ_INSERT_TAIL(&sender->vlan->send_queue, packet, entry);
>  
>      return packet->size;
>  }
> @@ -2330,6 +2324,7 @@ VLANState *qemu_find_vlan(int id, int allocate)
>      }
>      vlan = qemu_mallocz(sizeof(VLANState));
>      vlan->id = id;
> +    TAILQ_INIT(&vlan->send_queue);
>      vlan->next = NULL;
>      pvlan = &first_vlan;
>      while (*pvlan != NULL)
> diff --git a/net.h b/net.h
> index 3ac9e8c..bab02f5 100644
> --- a/net.h
> +++ b/net.h
> @@ -1,6 +1,7 @@
>  #ifndef QEMU_NET_H
>  #define QEMU_NET_H
>  
> +#include "sys-queue.h"
>  #include "qemu-common.h"
>  
>  /* VLANs support */
> @@ -35,7 +36,7 @@ typedef struct VLANPacket VLANPacket;
>  typedef void (NetPacketSent) (VLANClientState *, ssize_t);
>  
>  struct VLANPacket {
> -    struct VLANPacket *next;
> +    TAILQ_ENTRY(VLANPacket) entry;
>      VLANClientState *sender;
>      int size;
>      NetPacketSent *sent_cb;
> @@ -47,7 +48,7 @@ struct VLANState {
>      VLANClientState *first_client;
>      struct VLANState *next;
>      unsigned int nb_guest_devs, nb_host_devs;
> -    VLANPacket *send_queue;
> +    TAILQ_HEAD(send_queue, VLANPacket) send_queue;
>      int delivering;
>  };
>  
> 

Jan

-- 
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