Re: [PATCH] migration: use parameters.mode in cpr_state_save

[Steven Sistare <steven.sistare@oracle.com>]

On 2/5/2025 4:28 PM, Peter Xu wrote:
> On Wed, Feb 05, 2025 at 12:54:01PM -0800, Steve Sistare wrote:
>> qmp_migrate guarantees that cpr_channel is not null for
>> MIG_MODE_CPR_TRANSFER when cpr_state_save is called:
>>
>>      qmp_migrate()
>>          if (s->parameters.mode == MIG_MODE_CPR_TRANSFER && !cpr_channel) {
>>              return;
>>          }
>>          cpr_state_save(cpr_channel)
>>
>> but cpr_state_save checks for mode differently before using channel,
>> and Coverity cannot infer that they are equivalent in outgoing QEMU,
>> and warns that channel may be NULL:
>>
>>      cpr_state_save(channel)
>>          MigMode mode = migrate_mode();
>>          if (mode == MIG_MODE_CPR_TRANSFER) {
>>              f = cpr_transfer_output(channel, errp);
>>
>> To make Coverity happy, use parameters.mode in cpr_state_save.
>>
>> Resolves: Coverity CID 1590980
>> Reported-by: Peter Maydell <peter.maydell@linaro.org>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>   migration/cpr.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/migration/cpr.c b/migration/cpr.c
>> index 584b0b9..7f20bd5 100644
>> --- a/migration/cpr.c
>> +++ b/migration/cpr.c
>> @@ -8,6 +8,7 @@
>>   #include "qemu/osdep.h"
>>   #include "qapi/error.h"
>>   #include "migration/cpr.h"
>> +#include "migration/migration.h"
>>   #include "migration/misc.h"
>>   #include "migration/options.h"
>>   #include "migration/qemu-file.h"
>> @@ -132,7 +133,7 @@ int cpr_state_save(MigrationChannel *channel, Error **errp)
>>   {
>>       int ret;
>>       QEMUFile *f;
>> -    MigMode mode = migrate_mode();
>> +    MigMode mode = migrate_get_current()->parameters.mode;
> 
> Are we sure this can make coverity happy?

It should, based on Peter Maydell's analysis, but I would appreciate
if he could apply and test the fix.

> Another more straightforward change is caching migrate mode in
> qmp_migrate() and also check that before invoking cpr_state_save().

Surely anyone would consider my one-line change to be straight forward.

- Steve

>>       trace_cpr_state_save(MigMode_str(mode));
>>   
>> -- 
>> 1.8.3.1
>>
>