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Re: [libvirt] [PATCH] qemu_migrate: Fix assign the same port when migrating concurrently



On Fri, Sep 27, 2013 at 06:28:50 +0000, Wangyufei (A) wrote:
> From: WangYufei <james wangyufei huawei com>
> Date: Fri, 27 Sep 2013 11:53:57 +0800
> Subject: [PATCH] qemu_migrate: Fix assign the same port when migrating concurrently
> 
> When we migrate vms concurrently, there's a chance that libvirtd on destination assign the same port for different migrations, which will lead to migration failed during migration prepare phase on destination. So we change the port increase to atomic operation to solve the problem.

Oops, this was apparently latent until the big qemu driver lock was
removed.

> 
> Signed-off-by: WangYufei <james wangyufei huawei com>
> ---
>  src/qemu/qemu_migration.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> index 3a1aab7..0f496f4 100644
> --- a/src/qemu/qemu_migration.c
> +++ b/src/qemu/qemu_migration.c
> @@ -57,6 +57,7 @@
>  #include "virhook.h"
>  #include "virstring.h"
>  #include "virtypedparam.h"
> +#include "viratomic.h"
> 
>  #define VIR_FROM_THIS VIR_FROM_QEMU
> 
> @@ -2521,7 +2522,7 @@ qemuMigrationPrepareDirect(virQEMUDriverPtr driver,
>       * to be a correct hostname which refers to the target machine).
>       */
>      if (uri_in == NULL) {
> -        this_port = QEMUD_MIGRATION_FIRST_PORT + port++;
> +        this_port = QEMUD_MIGRATION_FIRST_PORT + virAtomicIntInc(&port);
>          if (port == QEMUD_MIGRATION_NUM_PORTS) port = 0;
> 
>          /* Get hostname */
> @@ -2578,7 +2579,7 @@ qemuMigrationPrepareDirect(virQEMUDriverPtr driver,
> 
>          if (uri->port == 0) {
>              /* Generate a port */
> -            this_port = QEMUD_MIGRATION_FIRST_PORT + port++;
> +            this_port = QEMUD_MIGRATION_FIRST_PORT + virAtomicIntInc(&port);
>              if (port == QEMUD_MIGRATION_NUM_PORTS)
>                  port = 0;
> 

Unfortunately, this patch is incomplete. The increments are now atomic
but the wrapping at QEMUD_MIGRATION_NUM_PORTS is not. I think this
should use virPortAllocator instead.

Jirka


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