Hello Michal, On 04/11/2018 02:04 PM, mhocko@xxxxxxxxxx wrote: > From: Michal Hocko <mhocko@xxxxxxxx> > > 4.17+ kernels offer a new MAP_FIXED_NOREPLACE flag which allows the caller to > atomicaly probe for a given address range. > > [wording heavily updated by John Hubbard <jhubbard@xxxxxxxxxx>] > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> Thanks! I've applied your patch, and done a little tweaking. The results have already been pushed. Cheers Michael > --- > Hi, > Andrew's sent the MAP_FIXED_NOREPLACE to Linus for the upcoming merge > window. So here we go with the man page update. > > man2/mmap.2 | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/man2/mmap.2 b/man2/mmap.2 > index ea64eb8f0dcc..f702f3e4eba2 100644 > --- a/man2/mmap.2 > +++ b/man2/mmap.2 > @@ -261,6 +261,27 @@ Examples include > and the PAM libraries > .UR http://www.linux-pam.org > .UE . > +Newer kernels > +(Linux 4.17 and later) have a > +.B MAP_FIXED_NOREPLACE > +option that avoids the corruption problem; if available, MAP_FIXED_NOREPLACE > +should be preferred over MAP_FIXED. > +.TP > +.BR MAP_FIXED_NOREPLACE " (since Linux 4.17)" > +Similar to MAP_FIXED with respect to the > +.I > +addr > +enforcement, but different in that MAP_FIXED_NOREPLACE never clobbers a pre-existing > +mapped range. If the requested range would collide with an existing > +mapping, then this call fails with > +.B EEXIST. > +This flag can therefore be used as a way to atomically (with respect to other > +threads) attempt to map an address range: one thread will succeed; all others > +will report failure. Please note that older kernels which do not recognize this > +flag will typically (upon detecting a collision with a pre-existing mapping) > +fall back to a "non-MAP_FIXED" type of behavior: they will return an address that > +is different than the requested one. Therefore, backward-compatible software > +should check the returned address against the requested address. > .TP > .B MAP_GROWSDOWN > This flag is used for stacks. > @@ -487,6 +508,12 @@ is not a valid file descriptor (and > .B MAP_ANONYMOUS > was not set). > .TP > +.B EEXIST > +range covered by > +.IR addr , > +.IR length > +is clashing with an existing mapping. > +.TP > .B EINVAL > We don't like > .IR addr , > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
