Re: kern/55541: mmap(2) needs some updates

[Valery Ushakov <uwe%stderr.spb.ru@localhost>]

The following reply was made to PR kern/55541; it has been noted by GNATS.

From: Valery Ushakov <uwe%stderr.spb.ru@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/55541: mmap(2) needs some updates
Date: Wed, 5 Aug 2020 18:19:53 +0300

 I'm not etnirely sure what your concern is.
 
 On Tue, Aug 04, 2020 at 23:35:01 +0000, coypu%sdf.org@localhost wrote:
 
 > If addr is non-zero, it is used as a hint to the system.
 > 
 > Without conditionalizing this on MAP_FIXED.
 
 I wonder if you are reading "MAP_FIXED" as implied by "hint" and then
 think it's a bug that it's implied and not explicit.  But I'm not sure
 it is the case.
 
 SUS says:
 
   When MAP_FIXED is set in the flags argument, the implementation is
   informed that the value of pa shall be addr, exactly. [...]
 
   When MAP_FIXED is not set, the implementation uses addr in an
   implementation-defined manner to arrive at pa. [...]
 
 I think hint is vague^Wbroad enough to be just the right word here.
 
 
 > Additionally, the behaviour of MAP_TRYFIXED might be wrong from the
 > actual behaviour. Two people recalled it as being "if the mapping
 > already exists, fail", because MAP_FIXED unmaps the previous
 > mapping.
 >
 > The manual page, however, claims it would take "addr" as a hint in
 > this situation.
 
 As I said, I don't think "hint" is a problem in general.  The bigger
 problem here is IMO the phrase "normally protected" which is very
 ambiguous.
 
 -uwe