On Mon, May 01, 2017 at 08:34:16PM +0200, Michael Kerrisk (man-pages) wrote: > Hi Mike, > > On 04/28/2017 11:45 AM, Mike Rapoprt wrote: > > > > > > On April 27, 2017 8:26:16 PM GMT+03:00, "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> wrote: > >> Hi Mike, > >> > >> I've applied this, but have some questions/points I think > >> further clarification. > >> > >> On 04/27/2017 04:14 PM, Mike Rapoport wrote: > >>> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> > >>> --- > >>> man2/userfaultfd.2 | 135 > >> ++++++++++++++++++++++++++++++++++++++++++++++++++--- > >>> 1 file changed, 128 insertions(+), 7 deletions(-) > >>> > >>> diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 > >>> index cfea5cb..44af3e4 100644 > >>> --- a/man2/userfaultfd.2 > >>> +++ b/man2/userfaultfd.2 > >>> @@ -75,7 +75,7 @@ flag in > >>> .PP > >>> When the last file descriptor referring to a userfaultfd object is > >> closed, > >>> all memory ranges that were registered with the object are > >> unregistered > >>> -and unread page-fault events are flushed. > >>> +and unread events are flushed. > >>> .\" > >>> .SS Usage > >>> The userfaultfd mechanism is designed to allow a thread in a > >> multithreaded > >>> @@ -99,6 +99,20 @@ In such non-cooperative mode, > >>> the process that monitors userfaultfd and handles page faults > >>> needs to be aware of the changes in the virtual memory layout > >>> of the faulting process to avoid memory corruption. > >>> + > >>> +Starting from Linux 4.11, > >>> +userfaultfd may notify the fault-handling threads about changes > >>> +in the virtual memory layout of the faulting process. > >>> +In addition, if the faulting process invokes > >>> +.BR fork (2) > >>> +system call, > >>> +the userfaultfd objects associated with the parent may be duplicated > >>> +into the child process and the userfaultfd monitor will be notified > >>> +about the file descriptor associated with the userfault objects > >> > >> What does "notified about the file descriptor" mean? > > > > Well, seems that I've made this one really awkward :) > > When the monitored process forks, all the userfault objects > > associated with it are duplicated into the child process. For each > > duplicated object, userfault generates event of type UFFD_EVENT_FORK > > and the uffdio_msg for this event contains the file descriptor that > > should be used to manipulate the duplicated userfault object. > > Hope this clarifies. > > Yes, it's clearer now. > > Mostly what was needed here was a forward reference that mentions > UFFD_EVENT_FORK explicitly. I added that, and also enhanced the > text on UFFD_EVENT_FORK a little. > > Also, it's not just fork(2) for which UFFD_EVENT_FORK is generated, > right? It can also be a clone(2) cal that does not specify > CLONE_VM, right? Yes. > Could you review my changes in commit 522ab2ff6fc9010432a > to make sure they are okay. Yes, thats correct and with your updates the text is much clearer. Thanks. > Cheers, > > Michael > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
