Re: [Qemu-devel] [PATCH 2/2] spapr_nvram: Enable migration

[Alexander Graf <agraf@suse.de>]

On 25.09.14 09:02, Alexey Kardashevskiy wrote:
> The only case when sPAPR NVRAM migrates now is if is backed by a file and
> copy-storage migration is performed.
> 
> This enables RAM copy of NVRAM even if NVRAM is backed by a file.
> 
> This defines a VMSTATE descriptor for NVRAM device so the memory copy
> of NVRAM can migrate and be written to a backing file on the destination
> if one is provided.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  hw/nvram/spapr_nvram.c | 68 +++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 59 insertions(+), 9 deletions(-)
> 
> diff --git a/hw/nvram/spapr_nvram.c b/hw/nvram/spapr_nvram.c
> index 6a72ef4..254009e 100644
> --- a/hw/nvram/spapr_nvram.c
> +++ b/hw/nvram/spapr_nvram.c
> @@ -76,15 +76,20 @@ static void rtas_nvram_fetch(PowerPCCPU *cpu, sPAPREnvironment *spapr,
>          return;
>      }
>  
> +    assert(nvram->buf);
> +
>      membuf = cpu_physical_memory_map(buffer, &len, 1);
> +
> +    alen = len;
>      if (nvram->drive) {
>          alen = bdrv_pread(nvram->drive, offset, membuf, len);
> +        if (alen > 0) {
> +            memcpy(nvram->buf + offset, membuf, alen);

Why?

> +        }
>      } else {
> -        assert(nvram->buf);
> -
>          memcpy(membuf, nvram->buf + offset, len);
> -        alen = len;
>      }
> +
>      cpu_physical_memory_unmap(membuf, len, 1, len);
>  
>      rtas_st(rets, 0, (alen < len) ? RTAS_OUT_HW_ERROR : RTAS_OUT_SUCCESS);
> @@ -122,14 +127,15 @@ static void rtas_nvram_store(PowerPCCPU *cpu, sPAPREnvironment *spapr,
>      }
>  
>      membuf = cpu_physical_memory_map(buffer, &len, 0);
> +
> +    alen = len;
>      if (nvram->drive) {
>          alen = bdrv_pwrite(nvram->drive, offset, membuf, len);
> -    } else {
> -        assert(nvram->buf);
> -
> -        memcpy(nvram->buf + offset, membuf, len);
> -        alen = len;
>      }
> +
> +    assert(nvram->buf);
> +    memcpy(nvram->buf + offset, membuf, len);
> +
>      cpu_physical_memory_unmap(membuf, len, 0, len);
>  
>      rtas_st(rets, 0, (alen < len) ? RTAS_OUT_HW_ERROR : RTAS_OUT_SUCCESS);
> @@ -144,9 +150,10 @@ static int spapr_nvram_init(VIOsPAPRDevice *dev)
>          nvram->size = bdrv_getlength(nvram->drive);
>      } else {
>          nvram->size = DEFAULT_NVRAM_SIZE;
> -        nvram->buf = g_malloc0(nvram->size);
>      }
>  
> +    nvram->buf = g_malloc0(nvram->size);
> +
>      if ((nvram->size < MIN_NVRAM_SIZE) || (nvram->size > MAX_NVRAM_SIZE)) {
>          fprintf(stderr, "spapr-nvram must be between %d and %d bytes in size\n",
>                  MIN_NVRAM_SIZE, MAX_NVRAM_SIZE);
> @@ -166,6 +173,48 @@ static int spapr_nvram_devnode(VIOsPAPRDevice *dev, void *fdt, int node_off)
>      return fdt_setprop_cell(fdt, node_off, "#bytes", nvram->size);
>  }
>  
> +static int spapr_nvram_pre_load(void *opaque)
> +{
> +    sPAPRNVRAM *nvram = VIO_SPAPR_NVRAM(opaque);
> +
> +    g_free(nvram->buf);
> +    nvram->buf = NULL;
> +    nvram->size = 0;
> +
> +    return 0;
> +}
> +
> +static int spapr_nvram_post_load(void *opaque, int version_id)
> +{
> +    sPAPRNVRAM *nvram = VIO_SPAPR_NVRAM(opaque);
> +
> +    if (nvram->drive) {
> +        int alen = bdrv_pwrite(nvram->drive, 0, nvram->buf, nvram->size);

In the file backed case you're already overwriting the disk backed
version, no?

Also, couldn't you just do the copy and provisioning of buf in a
pre_save hook?


Alex

> +
> +        if (alen < 0) {
> +            return alen;
> +        }
> +        if (alen != nvram->size) {
> +            return -1;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +static const VMStateDescription vmstate_spapr_nvram = {
> +    .name = "spapr_nvram",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .pre_load = spapr_nvram_pre_load,
> +    .post_load = spapr_nvram_post_load,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT32(size, sPAPRNVRAM),
> +        VMSTATE_VBUFFER_ALLOC_UINT32(buf, sPAPRNVRAM, 1, NULL, 0, size),
> +        VMSTATE_END_OF_LIST()
> +    },
> +};
> +
>  static Property spapr_nvram_properties[] = {
>      DEFINE_SPAPR_PROPERTIES(sPAPRNVRAM, sdev),
>      DEFINE_PROP_DRIVE("drive", sPAPRNVRAM, drive),
> @@ -184,6 +233,7 @@ static void spapr_nvram_class_init(ObjectClass *klass, void *data)
>      k->dt_compatible = "qemu,spapr-nvram";
>      set_bit(DEVICE_CATEGORY_MISC, dc->categories);
>      dc->props = spapr_nvram_properties;
> +    dc->vmsd = &vmstate_spapr_nvram;
>  }
>  
>  static const TypeInfo spapr_nvram_type_info = {
>