Re: [Qemu-devel] [RFC PATCH qemu] qapi: Add query-memory-checksum

[Alexey Kardashevskiy]

On 22/08/2019 11:33, Eric Blake wrote:
> On 8/21/19 8:16 PM, Alexey Kardashevskiy wrote:
> > This returns MD5 checksum of all RAM blocks for migration debugging
> > as this is way faster than saving the entire RAM to a file and checking
> > that.
> >
> > Signed-off-by: Alexey Kardashevskiy <address@hidden>
> > ---
> >
> >
> > I am actually wondering if there is an easier way of getting these
> > checksums and I just do not see it, it cannot be that we fixed all
> > memory migration bugs :)
>
> I'm not sure whether the command itself makes sense, but for the interface:
>
>
> > +++ b/qapi/misc.json
> > @@ -1194,6 +1194,33 @@
> >   ##
> >   { 'command': 'query-memory-size-summary', 'returns': 'MemoryInfo' }
> >   
> > +##
> > +# @MemoryChecksum:
> > +#
> > +# A string with MD5 checksum of all RAMBlocks.
> > +#
> > +# @checksum: the checksum.
> > +#
> > +# Since: 3.2.0
>
> This should be 4.2, not 3.2.
>
> > +##
> > +{ 'struct': 'MemoryChecksum',
> > +  'data'  : { 'checksum': 'str' } }
> > +
> > +##
> > +# @query-memory-checksum:
> > +#
> > +# Return the MD5 checksum of all RAMBlocks.
> > +#
> > +# Example:
> > +#
> > +# -> { "execute": "query-memory-checksum" }
> > +# <- { "return": { "checksum": "a0880304994f64cb2edad77b9a1cd58f" } }
> > +#
> > +# Since: 3.2.0
>
> and again
>
> > +##
> > +{ 'command': 'query-memory-checksum',
> > +  'returns': 'MemoryChecksum' }
> > +
> >   
>
> > +++ b/exec.c
> > @@ -2050,6 +2050,22 @@ void *qemu_ram_get_host_addr(RAMBlock *rb)
> >       return rb->host;
> >   }
> >   
> > +gchar *qemu_ram_chksum(void)
>
> gchar is a pointless glib type.  Use 'char' instead.
>
> > +{
> > +    struct RAMBlock *rb;
> > +    GChecksum *chksum = g_checksum_new(G_CHECKSUM_MD5);
> > +    gchar *ret;
> > +
> > +    RAMBLOCK_FOREACH(rb) {
> > +        g_checksum_update(chksum, qemu_ram_get_host_addr(rb),
> > +                          qemu_ram_get_used_length(rb));
> > +    }
> > +    ret = g_strdup(g_checksum_get_string(chksum));
> > +    g_checksum_free(chksum);
> > +
> > +    return ret;
> > +}
>
> How long does this take to run?  Is it something where you really want
> to block the guest while chewing over the guest's entire memory?


10-20 times faster than "pmemsave" and blocking the guest is not a 
problem here as both - source and destination - guests are stopped 
(otherwise the checksum does not make sense).



--
Alexey