On Thu, Apr 12, 2018 at 8:37 PM, Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx> wrote: > Hi John, > > On 12 April 2018 at 20:33, John Hubbard <jhubbard@xxxxxxxxxx> wrote: >> On 04/12/2018 08:39 AM, Jann Horn wrote: >>> Clarify that MAP_FIXED is appropriate if the specified address range has >>> been reserved using an existing mapping, but shouldn't be used otherwise. >>> >>> Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> >>> --- >>> man2/mmap.2 | 19 +++++++++++-------- >>> 1 file changed, 11 insertions(+), 8 deletions(-) >>> >>> diff --git a/man2/mmap.2 b/man2/mmap.2 [...] >>> .IP >>> For example, suppose that thread A looks through >>> @@ -284,13 +285,15 @@ and the PAM libraries >>> .UR http://www.linux-pam.org >>> .UE . >>> .IP >>> -Newer kernels >>> -(Linux 4.17 and later) have a >>> +For cases in which the specified memory region has not been reserved using an >>> +existing mapping, newer kernels (Linux 4.17 and later) provide an option >>> .B MAP_FIXED_NOREPLACE >>> -option that avoids the corruption problem; if available, >>> -.B MAP_FIXED_NOREPLACE >>> -should be preferred over >>> -.BR MAP_FIXED . >>> +that should be used instead; older kernels require the caller to use >>> +.I addr >>> +as a hint (without >>> +.BR MAP_FIXED ) >> >> Here, I got lost: the sentence suddenly jumps into explaining non-MAP_FIXED >> behavior, in the MAP_FIXED section. Maybe if you break up the sentence, and >> possibly omit non-MAP_FIXED discussion, it will help. > > Hmmm -- true. That piece could be a little clearer. How about something like this? For cases in which MAP_FIXED can not be used because the specified memory region has not been reserved using an existing mapping, newer kernels (Linux 4.17 and later) provide an option MAP_FIXED_NOREPLACE that should be used instead. Older kernels require the caller to use addr as a hint and take appropriate action if the kernel places the new mapping at a different address. John, Michael, what do you think? > Jann, I've already pushed the existing patch. Do you want to add a patch on top?
