[libvirt RFCv7 34/40] qemu: saveimage: add multifd-compression field to save format

[Claudio Fontana]

On 5/6/22 4:32 PM, Claudio Fontana wrote:
> One thing I was thinking about, beyond what is in this patch,
> 
> is that for the QEMU driver we could save the number of channels used for the --parallel save in the qemu SaveImage header as well.
> 
> This way, on restore libvirt would automatically know how many file it needs to load, and the
> user does not need to know beforehand which --parallel-connections NN to use.
> 
> Still the --parallel on resume would be needed in the current design, but that could theoretically be dropped as well.
> However, I wonder if that would create issues for other hypervisors implementing this, ie I presume keeping the --parallel flag would be the safest option.

, ... ie I presume keeping the --parallel flag as a mandatory parameter to the virsh restore command when restoring from a parallel saved image would be the safest option.

> 
> Thanks,
> 
> Claudio
> 
> 
> On 5/6/22 3:11 PM, Claudio Fontana wrote:
>> Signed-off-by: Claudio Fontana <cfontana at suse.de>
>> ---
>>  src/qemu/qemu_saveimage.c | 19 ++++++++++++++++++-
>>  src/qemu/qemu_saveimage.h |  5 +++--
>>  2 files changed, 21 insertions(+), 3 deletions(-)
>>
>> diff --git a/src/qemu/qemu_saveimage.c b/src/qemu/qemu_saveimage.c
>> index 35a75069e8..c0920c5baa 100644
>> --- a/src/qemu/qemu_saveimage.c
>> +++ b/src/qemu/qemu_saveimage.c
>> @@ -67,6 +67,23 @@ VIR_ENUM_IMPL(qemuSaveCompression,
>>                "lzop",
>>  );
>>  
>> +typedef enum {
>> +    QEMU_SAVE_MULTIFD_COMP_NONE = 0,
>> +    QEMU_SAVE_MULTIFD_COMP_ZLIB = 1,
>> +    QEMU_SAVE_MULTIFD_COMP_ZSTD = 2,
>> +
>> +    /* used for the on-disk format, do not change/re-use numbers */
>> +    QEMU_SAVE_MULTIFD_COMP_LAST
>> +} virQEMUSaveMultiFdComp;
>> +
>> +VIR_ENUM_DECL(qemuSaveMultiFdComp);
>> +VIR_ENUM_IMPL(qemuSaveMultiFdComp,
>> +              QEMU_SAVE_MULTIFD_COMP_LAST,
>> +              "none",
>> +              "zlib",
>> +              "zstd",
>> +);
>> +
>>  static inline void
>>  qemuSaveImageBswapHeader(virQEMUSaveHeader *hdr)
>>  {
>> @@ -882,7 +899,7 @@ qemuSaveImageStartVM(virConnectPtr conn,
>>                                   virDomainXMLOptionGetSaveCookie(driver->xmlopt)) < 0)
>>          goto cleanup;
>>  
>> -    if ((header->version == 2) &&
>> +    if ((header->version >= 2) &&
>>          (header->compressed != QEMU_SAVE_FORMAT_RAW)) {
>>          if (!(cmd = qemuSaveImageGetCompressionCommand(header->compressed)))
>>              goto cleanup;
>> diff --git a/src/qemu/qemu_saveimage.h b/src/qemu/qemu_saveimage.h
>> index ae7b3faa17..eb0734101e 100644
>> --- a/src/qemu/qemu_saveimage.h
>> +++ b/src/qemu/qemu_saveimage.h
>> @@ -30,7 +30,7 @@
>>   */
>>  #define QEMU_SAVE_MAGIC   "LibvirtQemudSave"
>>  #define QEMU_SAVE_PARTIAL "LibvirtQemudPart"
>> -#define QEMU_SAVE_VERSION 2
>> +#define QEMU_SAVE_VERSION 3
>>  
>>  G_STATIC_ASSERT(sizeof(QEMU_SAVE_MAGIC) == sizeof(QEMU_SAVE_PARTIAL));
>>  
>> @@ -42,7 +42,8 @@ struct _virQEMUSaveHeader {
>>      uint32_t was_running;
>>      uint32_t compressed;
>>      uint32_t cookieOffset;
>> -    uint32_t unused[14];
>> +    uint32_t multifd_comp;
>> +    uint32_t unused[13];
>>  };
>>  
>>  
>>
>