Re: [Qemu-devel] [PATCH 3/4] virtio-9p: Wait for 9p operations to complete before migration.

[Paolo Bonzini <pbonzini@redhat.com>]

Il 11/04/2013 14:14, Benoît Canet ha scritto:
> The function used to wait is registered as a pre migration flush hook.
> 
> The completion status is put in the virtio ring buffer which
> will be send to the guest on resume by the viring migration code
> 
> This patch is a rewrite from the one written by Aneesh Kumar.
> 
> Signed-off-by: Benoit Canet <benoit@irqsave.net>
> ---
>  hw/9pfs/virtio-9p-device.c |    2 ++
>  hw/9pfs/virtio-9p.c        |   70 ++++++++++++++++++++++++++++++++++++++++++++
>  hw/9pfs/virtio-9p.h        |    2 ++
>  3 files changed, 74 insertions(+)
> 
> diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
> index 7d4aefd..02b8630 100644
> --- a/hw/9pfs/virtio-9p-device.c
> +++ b/hw/9pfs/virtio-9p-device.c
> @@ -200,6 +200,8 @@ VirtIODevice *virtio_9p_init(DeviceState *dev, V9fsConf *conf)
>      V9fsPath path;
>      static int virtio_9p_id;
>  
> +    v9fs_init_migration_helper();
> +
>      s = (V9fsState *)virtio_common_init("virtio-9p",
>                                      VIRTIO_ID_9P,
>                                      sizeof(struct virtio_9p_config)+
> diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
> index 5cc4c92..3bf3ee4 100644
> --- a/hw/9pfs/virtio-9p.c
> +++ b/hw/9pfs/virtio-9p.c
> @@ -20,11 +20,20 @@
>  #include "virtio-9p-coth.h"
>  #include "trace.h"
>  #include "migration/migration.h"
> +#include "migration/migration-flush-hooks.h"
>  
>  int open_fd_hw;
>  int total_open_fd;
>  static int open_fd_rc;
>  
> +typedef struct MigrationHelper {
> +    int32_t pending_requests;
> +    QemuCond complete;
> +    QemuMutex mutex;
> +} MigrationHelper;
> +
> +MigrationHelper *migration;

I say, just use three variables instead of a struct.

Paolo

>  enum {
>      Oread   = 0x00,
>      Owrite  = 0x01,
> @@ -37,6 +46,62 @@ enum {
>      Oappend = 0x80,
>  };
>  
> +static void v9fs_wait_for_requests_drain(void)
> +{
> +    if (!migration) {
> +        return;
> +    }
> +
> +    qemu_mutex_lock(&migration->mutex);
> +    while (migration->pending_requests) {
> +        /* At this point ticks and vcpus will be stopped so we can safely
> +         * release the BQL so pending 9p callbacks will be executed and the
> +         * condition signaled.
> +         */
> +        qemu_mutex_unlock_iothread();
> +        qemu_cond_wait(&migration->complete, &migration->mutex);
> +        qemu_mutex_lock_iothread();
> +    }
> +    qemu_mutex_unlock(&migration->mutex);
> +}
> +
> +void v9fs_init_migration_helper(void)
> +{
> +    if (migration) {
> +        return;
> +    }
> +
> +    migration = g_new0(MigrationHelper, 1);
> +    qemu_mutex_init(&migration->mutex);
> +    qemu_cond_init(&migration->complete);
> +    register_migration_flush_hook(v9fs_wait_for_requests_drain);
> +}
> +
> +static void v9fs_inc_pending_requests(void)
> +{
> +    if (!migration) {
> +        return;
> +    }
> +
> +    qemu_mutex_lock(&migration->mutex);
> +    migration->pending_requests++;
> +    qemu_mutex_unlock(&migration->mutex);
> +}
> +
> +static void v9fs_dec_pending_requests(void)
> +{
> +    if (!migration) {
> +        return;
> +    }
> +
> +    qemu_mutex_lock(&migration->mutex);
> +    migration->pending_requests--;
> +    if (!migration->pending_requests) {
> +        qemu_cond_signal(&migration->complete);
> +    }
> +    qemu_mutex_unlock(&migration->mutex);
> +}
> +
>  static int omode_to_uflags(int8_t mode)
>  {
>      int ret = 0;
> @@ -637,6 +702,8 @@ static void complete_pdu(V9fsState *s, V9fsPDU *pdu, ssize_t len)
>      qemu_co_queue_next(&pdu->complete);
>  
>      free_pdu(s, pdu);
> +
> +    v9fs_dec_pending_requests();
>  }
>  
>  static mode_t v9mode_to_mode(uint32_t mode, V9fsString *extension)
> @@ -3240,6 +3307,9 @@ static void submit_pdu(V9fsState *s, V9fsPDU *pdu)
>      if (is_ro_export(&s->ctx) && !is_read_only_op(pdu)) {
>          handler = v9fs_fs_ro;
>      }
> +
> +    v9fs_inc_pending_requests();
> +
>      co = qemu_coroutine_create(handler);
>      qemu_coroutine_enter(co, pdu);
>  }
> diff --git a/hw/9pfs/virtio-9p.h b/hw/9pfs/virtio-9p.h
> index 52b1c69..4d16d46 100644
> --- a/hw/9pfs/virtio-9p.h
> +++ b/hw/9pfs/virtio-9p.h
> @@ -401,4 +401,6 @@ extern int v9fs_name_to_path(V9fsState *s, V9fsPath *dirpath,
>  #define pdu_unmarshal(pdu, offset, fmt, args...)  \
>      v9fs_unmarshal(pdu->elem.out_sg, pdu->elem.out_num, offset, 1, fmt, ##args)
>  
> +void v9fs_init_migration_helper(void);
> +
>  #endif
>