Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> --- man2/ioctl_userfaultfd.2 | 53 ++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 51 insertions(+), 2 deletions(-) diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2 index 42bf7a7..cdc07e0 100644 --- a/man2/ioctl_userfaultfd.2 +++ b/man2/ioctl_userfaultfd.2 @@ -121,22 +121,70 @@ and explicitly enable userfaultfd features that are disabled by default. The kernel always reports all the available features in the .I features field. + +To enable userfaultfd features the application should set +a bit corresponding to each feature it wants to enable in the +.I features +field. +If the kernel supports all the requested features it will enable them. +Otherwise it will zero out the returned +.I uffdio_api +structure and return +.BR EINVAL . .\" FIXME add more details about feature negotiation and enablement Since Linux 4.11, the following feature bits may be set: .TP .B UFFD_FEATURE_EVENT_FORK +When this feature is enabled, +the userfaultfd objects associated with a parent process are duplicated +into the child process during +.BR fork (2) +system call and the +.I UFFD_EVENT_FORK +is delivered to the userfaultfd monitor .TP .B UFFD_FEATURE_EVENT_REMAP +If this feature is enabled, +when the faulting process invokes +.BR mremap (2) +system call +the userfaultfd monitor will receive an event of type +.I UFFD_EVENT_REMAP. .TP .B UFFD_FEATURE_EVENT_REMOVE +If this feature is enabled, +when the faulting process calls +.BR madvise(2) +system call with +.I MADV_DONTNEED +or +.I MADV_REMOVE +advice to free a virtual memory area +the userfaultfd monitor will receive an event of type +.I UFFD_EVENT_REMOVE. .TP .B UFFD_FEATURE_EVENT_UNMAP +If this feature is enabled, +when the faulting process unmaps virtual memory either explicitly with +.BR munmap (2) +system call, or implicitly either during +.BR mmap (2) +or +.BR mremap (2) +system call, +the userfaultfd monitor will receive an event of type +.I UFFD_EVENT_UNMAP .TP .B UFFD_FEATURE_MISSING_HUGETLBFS +If this feature bit is set, +the kernel supports registering userfaultfd ranges on hugetlbfs +virtual memory areas .TP .B UFFD_FEATURE_MISSING_SHMEM -.\" FIXME add feature description +If this feature bit is set, +the kernel supports registering userfaultfd ranges on tmpfs +virtual memory areas The returned .I ioctls @@ -182,7 +230,8 @@ The API version requested in the .I api field is not supported by this kernel, or the .I features -field was not zero. +field passed to the kernel includes feature bits that are not supported +by the current kernel version. .\" FIXME In the above error case, the returned 'uffdio_api' structure is .\" zeroed out. Why is this done? This should be explained in the manual page. .\" -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
