Re: [PATCH v6 COLO 06/15] libxc/save: support COLO save

[Yang Hongyang <yanghy@cn.fujitsu.com>]

On 06/08/2015 09:04 PM, Andrew Cooper wrote:
> On 08/06/15 04:45, Yang Hongyang wrote:
>> call callbacks->get_dirty_pfn() after suspend primary vm to
>> get dirty pages on secondary vm, and send pages both dirty on
>> primary/secondary to secondary.
>>
>> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
>> CC: Andrew Cooper <andrew.cooper3@citrix.com>
>> ---
>>   tools/libxc/xc_sr_save.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 48 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/libxc/xc_sr_save.c b/tools/libxc/xc_sr_save.c
>> index d63b783..cda61ed 100644
>> --- a/tools/libxc/xc_sr_save.c
>> +++ b/tools/libxc/xc_sr_save.c
>> @@ -515,6 +515,31 @@ static int send_memory_live(struct xc_sr_context *ctx)
>>       return rc;
>>   }
>>
>> +static int update_dirty_bitmap(uint8_t *(*get_dirty_pfn)(void *), void *data,
>> +                               unsigned long p2m_size, unsigned long *bitmap)
>
> This function should take a ctx rather than having the caller expand 3
> parameters.  Also, "update_dirty_bitmap" is a little misleading, as it
> isn't querying the hypervisor for the dirty bitmap.

ok.

>
>> +{
>> +    uint64_t *pfn_list;
>> +    uint64_t count, i;
>> +    uint64_t pfn;
>> +
>> +    pfn_list = (uint64_t *)get_dirty_pfn(data);
>
> This looks like a recipe for width-errors.  The get_dirty_pfn() call
> should take a pointer to a struct for it to fill.

but the size is unknown for the caller.pfn_list[0] is the count of
pfn.

>
>> +    assert(pfn_list);
>
> This should turn into an error rather than an abort().

Even if there are no dirty pages on secondary, pfn_list shouldn't be
NULL, it's just that pfn_list[0] will be 0. if pfn_list is NULL,
there might be unexpected error happened.

>
>> +
>> +    count = pfn_list[0];
>> +    for (i = 0; i < count; i++) {
>
> style
>
>> +        pfn = pfn_list[i + 1];
>> +        if (pfn > p2m_size) {
>> +            errno = EINVAL;
>> +            return -1;
>> +        }
>> +
>> +        set_bit(pfn, bitmap);
>> +    }
>> +
>> +    free(pfn_list);
>> +    return 0;
>> +}
>> +
>>   /*
>>    * Suspend the domain and send dirty memory.
>>    * This is the last iteration of the live migration and the
>> @@ -555,6 +580,19 @@ static int suspend_and_send_dirty(struct xc_sr_context *ctx)
>>
>>       bitmap_or(dirty_bitmap, ctx->save.deferred_pages, ctx->save.p2m_size);
>>
>> +    if ( !ctx->save.live && ctx->save.callbacks->get_dirty_pfn )
>> +    {
>
> Shouldn't get_dirty_pfn be mandatory for COLO streams (even if it is a
> noop to start with) ?

It should be mandatory, it shouldn't be noop under COLO. perhaps we should
add sanity check at the beginning. But problem is save side do not have a param
passed from libxl to indicate the stream type(like checkpointed_stream in
restore side). So we may need to add another XCFLAGS? Currently there is
XCFLAGS_CHECKPOINTED which represents Remus, we might need to change this to
XCFLAGS_STREAM_REMUS
XCFLAGS_STREAM_COLO
so that we can know what kind of stream we are handling?

>
> ~Andrew
>
>> +        rc = update_dirty_bitmap(ctx->save.callbacks->get_dirty_pfn,
>> +                                 ctx->save.callbacks->data,
>> +                                 ctx->save.p2m_size,
>> +                                 dirty_bitmap);
>> +        if ( rc )
>> +        {
>> +            PERROR("Failed to get secondary vm's dirty pages");
>> +            goto out;
>> +        }
>> +    }
>> +
>>       rc = send_dirty_pages(ctx, stats.dirty_count + ctx->save.nr_deferred_pages);
>>       if ( rc )
>>           goto out;
>> @@ -784,7 +822,16 @@ static int save(struct xc_sr_context *ctx, uint16_t guest_type)
>>               if ( rc )
>>                   goto err;
>>
>> -            ctx->save.callbacks->postcopy(ctx->save.callbacks->data);
>> +            rc = ctx->save.callbacks->postcopy(ctx->save.callbacks->data);
>> +            if ( !rc ) {
>> +                if ( !errno )
>> +                {
>> +                    /* Postcopy request failed (without errno, using EINVAL) */
>> +                    errno = EINVAL;
>> +                }
>> +                rc = -1;
>> +                goto err;
>> +            }
>>
>>               rc = ctx->save.callbacks->checkpoint(ctx->save.callbacks->data);
>>               if ( rc <= 0 )
>
> .
>

-- 
Thanks,
Yang.