Re: [Qemu-devel] [PATCH V6 02/10] migration: pass MigrationIncomingState* into migration check functions

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Alexey Perevalov (a.perevalov@samsung.com) wrote:
> On 05/31/2017 08:54 PM, Dr. David Alan Gilbert wrote:
> > * Alexey Perevalov (a.perevalov@samsung.com) wrote:
> > > That tiny refactoring is necessary to be able to set
> > > UFFD_FEATURE_THREAD_ID while requesting features, and then
> > > to create downtime context in case when kernel supports it.
> > > 
> > > Signed-off-by: Alexey Perevalov <a.perevalov@samsung.com>
> > > ---
> > >   migration/migration.c    |  2 +-
> > >   migration/postcopy-ram.c | 10 +++++-----
> > >   migration/postcopy-ram.h |  2 +-
> > >   migration/savevm.c       |  2 +-
> > >   4 files changed, 8 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/migration/migration.c b/migration/migration.c
> > > index 0304c01..d735976 100644
> > > --- a/migration/migration.c
> > > +++ b/migration/migration.c
> > > @@ -789,7 +789,7 @@ void qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
> > >            * special support.
> > >            */
> > >           if (!old_postcopy_cap && runstate_check(RUN_STATE_INMIGRATE) &&
> > > -            !postcopy_ram_supported_by_host()) {
> > > +            !postcopy_ram_supported_by_host(NULL)) {
> > Why is that NULL rather than migration_incoming_get_current()?
> > That's on the destination.
> In current implementation, AFAIU,
> migrate-set-capabilities with postcopy-ram argument should be done on source
> machine only,
> and it's not required on destination. And it is unnecessary requirement to
> support userfaultfd on
> source and check it there.

Note the 'runstate_check(RUN_STATE_INMIGRATE)' - this check is made on
the destination.
While it's not strictly necessary for the management layer to do a
migrate_set_capability postcopy-ram   on the destination, it does it
anyway to check the destination is capable of postcopy before it starts
migration.

Dave

> 
> > 
> > Dave
> > 
> > >               /* postcopy_ram_supported_by_host will have emitted a more
> > >                * detailed message
> > >                */
> > > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> > > index a0489f6..4adab36 100644
> > > --- a/migration/postcopy-ram.c
> > > +++ b/migration/postcopy-ram.c
> > > @@ -59,7 +59,7 @@ struct PostcopyDiscardState {
> > >   #include <sys/eventfd.h>
> > >   #include <linux/userfaultfd.h>
> > > -static bool ufd_version_check(int ufd)
> > > +static bool ufd_version_check(int ufd, MigrationIncomingState *mis)
> > >   {
> > >       struct uffdio_api api_struct;
> > >       uint64_t ioctl_mask;
> > > @@ -112,7 +112,7 @@ static int test_range_shared(const char *block_name, void *host_addr,
> > >    * normally fine since if the postcopy succeeds it gets turned back on at the
> > >    * end.
> > >    */
> > > -bool postcopy_ram_supported_by_host(void)
> > > +bool postcopy_ram_supported_by_host(MigrationIncomingState *mis)
> > >   {
> > >       long pagesize = getpagesize();
> > >       int ufd = -1;
> > > @@ -135,7 +135,7 @@ bool postcopy_ram_supported_by_host(void)
> > >       }
> > >       /* Version and features check */
> > > -    if (!ufd_version_check(ufd)) {
> > > +    if (!ufd_version_check(ufd, mis)) {
> > >           goto out;
> > >       }
> > > @@ -512,7 +512,7 @@ int postcopy_ram_enable_notify(MigrationIncomingState *mis)
> > >        * Although the host check already tested the API, we need to
> > >        * do the check again as an ABI handshake on the new fd.
> > >        */
> > > -    if (!ufd_version_check(mis->userfault_fd)) {
> > > +    if (!ufd_version_check(mis->userfault_fd, mis)) {
> > >           return -1;
> > >       }
> > > @@ -650,7 +650,7 @@ void *postcopy_get_tmp_page(MigrationIncomingState *mis)
> > >   #else
> > >   /* No target OS support, stubs just fail */
> > > -bool postcopy_ram_supported_by_host(void)
> > > +bool postcopy_ram_supported_by_host(MigrationIncomingState *mis)
> > >   {
> > >       error_report("%s: No OS support", __func__);
> > >       return false;
> > > diff --git a/migration/postcopy-ram.h b/migration/postcopy-ram.h
> > > index 52d51e8..587a8b8 100644
> > > --- a/migration/postcopy-ram.h
> > > +++ b/migration/postcopy-ram.h
> > > @@ -14,7 +14,7 @@
> > >   #define QEMU_POSTCOPY_RAM_H
> > >   /* Return true if the host supports everything we need to do postcopy-ram */
> > > -bool postcopy_ram_supported_by_host(void);
> > > +bool postcopy_ram_supported_by_host(MigrationIncomingState *mis);
> > >   /*
> > >    * Make all of RAM sensitive to accesses to areas that haven't yet been written
> > > diff --git a/migration/savevm.c b/migration/savevm.c
> > > index f5e8194..61a6df7 100644
> > > --- a/migration/savevm.c
> > > +++ b/migration/savevm.c
> > > @@ -1356,7 +1356,7 @@ static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis)
> > >           return -1;
> > >       }
> > > -    if (!postcopy_ram_supported_by_host()) {
> > > +    if (!postcopy_ram_supported_by_host(mis)) {
> > >           postcopy_state_set(POSTCOPY_INCOMING_NONE);
> > >           return -1;
> > >       }
> > > -- 
> > > 1.8.3.1
> > > 
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> > 
> > 
> > 
> 
> -- 
> Best regards,
> Alexey Perevalov
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK