Re: [Qemu-devel] [PATCH 3/6] migration: add UFFD_FEATURE_THREAD_ID feature support

[Dr. David Alan Gilbert]

* Alexey Perevalov (address@hidden) wrote:
> Userfaultfd mechanism is able to provide process thread id,
> in case when client request it with UFDD_API ioctl.
> 
> Signed-off-by: Alexey Perevalov <address@hidden>

There seem to be two parts to this:
  a) Adding the mis parameter to ufd_version_check
  b) Asking for the feature

Please split it into two patches.

Also....

> ---
>  include/migration/postcopy-ram.h |  2 +-
>  migration/migration.c            |  2 +-
>  migration/postcopy-ram.c         | 12 ++++++------
>  migration/savevm.c               |  2 +-
>  4 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/include/migration/postcopy-ram.h 
> b/include/migration/postcopy-ram.h
> index 8e036b9..809f6db 100644
> --- a/include/migration/postcopy-ram.h
> +++ b/include/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/migration.c b/migration/migration.c
> index ad4036f..79f6425 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -802,7 +802,7 @@ 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)) {
>              /* 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 dc80dbb..70f0480 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -60,13 +60,13 @@ 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;
>  
>      api_struct.api = UFFD_API;
> -    api_struct.features = 0;
> +    api_struct.features = UFFD_FEATURE_THREAD_ID;
>      if (ioctl(ufd, UFFDIO_API, &api_struct)) {
>          error_report("postcopy_ram_supported_by_host: UFFDIO_API failed: %s",
>                       strerror(errno));

You're not actually using the 'mis' here - what I'd expected was
something that was going to check if the UFFDIO_API return said that it really
had the feature, and if so store a flag in the MIS somewhere.

Also, I'm not sure it's right to set 'api_struct.features' on the input - what
happens if this is run on an old kernel - we don't want postcopy to fail on
an old kernel without your feature.
I'm not 100% sure of the interface, but I think the way it works is you set
features = 0 before the call, and then check the api_struct.features in the
return - in the same way that I check for UFFD_FEATURE_MISSING_HUGETLBFS.

Dave

> @@ -113,7 +113,7 @@ 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;
> @@ -136,7 +136,7 @@ bool postcopy_ram_supported_by_host(void)
>      }
>  
>      /* Version and features check */
> -    if (!ufd_version_check(ufd)) {
> +    if (!ufd_version_check(ufd, mis)) {
>          goto out;
>      }
>  
> @@ -515,7 +515,7 @@ 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;
>      }
>  
> @@ -653,7 +653,7 @@ 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/savevm.c b/migration/savevm.c
> index 3b19a4a..f01e418 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1360,7 +1360,7 @@ 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 / address@hidden / Manchester, UK