On Tue, May 23, 2017 at 02:31:05PM +0300, Alexey Perevalov wrote: > This modification is necessary for userfault fd features which are > required to be requested from userspace. > UFFD_FEATURE_THREAD_ID is a one of such "on demand" feature, which will > be introduced in the next patch. > > QEMU have to use separate userfault file descriptor, due to > userfault context has internal state, and after first call of > ioctl UFFD_API it changes its state to UFFD_STATE_RUNNING (in case of > success), but kernel while handling ioctl UFFD_API expects > UFFD_STATE_WAIT_API. > So only one ioctl with UFFD_API is possible per ufd. > > Signed-off-by: Alexey Perevalov <a.pereva...@samsung.com>
Hi, Alexey, Mostly good to me, some nitpicks below. > --- > migration/postcopy-ram.c | 100 > ++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 91 insertions(+), 9 deletions(-) > > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index 3ed78bf..4f3f495 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -59,32 +59,114 @@ struct PostcopyDiscardState { > #include <sys/eventfd.h> > #include <linux/userfaultfd.h> > > -static bool ufd_version_check(int ufd, MigrationIncomingState *mis) > + > +/** > + * receive_ufd_features: check userfault fd features, to request only > supported > + * features in the future. > + * > + * Returns: true on success > + * > + * __NR_userfaultfd - should be checked before I don't see this line necessary. After all we will detect the error no matter what... > + * @features: out parameter will contain uffdio_api.features provided by > kernel > + * in case of success > + */ > +static bool receive_ufd_features(uint64_t *features) > { > - struct uffdio_api api_struct; > - uint64_t ioctl_mask; > + struct uffdio_api api_struct = {0}; > + int ufd; > + bool ret = true; > + > + /* if we are here __NR_userfaultfd should exists */ > + ufd = syscall(__NR_userfaultfd, O_CLOEXEC); > + if (ufd == -1) { > + error_report("%s: syscall __NR_userfaultfd failed: %s", __func__, > + strerror(errno)); > + return false; > + } > > + /* ask features */ > api_struct.api = UFFD_API; > api_struct.features = 0; > if (ioctl(ufd, UFFDIO_API, &api_struct)) { > - error_report("%s: UFFDIO_API failed: %s", __func__ > + error_report("%s: UFFDIO_API failed: %s", __func__, > strerror(errno)); > + ret = false; > + goto release_ufd; > + } > + > + *features = api_struct.features; > + > +release_ufd: > + close(ufd); > + return ret; > +} > + > +/** > + * request_ufd_features: this function should be called only once on a newly > + * opened ufd, subsequent calls will lead to error. > + * > + * Returns: true on succes > + * > + * @ufd: fd obtained from userfaultfd syscall > + * @features: bit mask see UFFD_API_FEATURES > + */ > +static bool request_ufd_features(int ufd, uint64_t features) > +{ > + struct uffdio_api api_struct = {0}; > + uint64_t ioctl_mask; > + > + api_struct.api = UFFD_API; > + api_struct.features = features; > + if (ioctl(ufd, UFFDIO_API, &api_struct)) { > + error_report("%s failed: UFFDIO_API failed: %s", __func__, > + strerror(errno)); Maybe we can indent this line to follow this file's rule? error_report("%s failed: UFFDIO_API failed: %s", __func__, strerror(errno)); > return false; > } > > - ioctl_mask = (__u64)1 << _UFFDIO_REGISTER | > - (__u64)1 << _UFFDIO_UNREGISTER; > + ioctl_mask = 1 << _UFFDIO_REGISTER | > + 1 << _UFFDIO_UNREGISTER; Could I ask why we explicitly removed (__u64) here? Since I see the old one better. > if ((api_struct.ioctls & ioctl_mask) != ioctl_mask) { > error_report("Missing userfault features: %" PRIx64, > (uint64_t)(~api_struct.ioctls & ioctl_mask)); > return false; > } > > + return true; > +} > + > +static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis) > +{ > + uint64_t asked_features = 0; > + static uint64_t supported_features; > + > + /* > + * it's not possible to > + * request UFFD_API twice per one fd > + * userfault fd features is persistent > + */ > + if (!supported_features) { I would prefer not having this static variable. After all, this function call is rare, and the receive_ufd_features() is not that slow as well. > + if (!receive_ufd_features(&supported_features)) { > + error_report("%s failed", __func__); > + return false; > + } > + } > + > + /* > + * request features, even if asked_features is 0, due to > + * kernel expects UFFD_API before UFFDIO_REGISTER, per > + * userfault file descriptor > + */ > + if (!request_ufd_features(ufd, asked_features)) { > + error_report("%s failed: features %" PRIu64, __func__, > + asked_features); Better indent? Thanks, -- Peter Xu