Re: [PATCH v2 0/2] mm: introduce MAP_FIXED_SAFE

[Edward Napierala]

On 1214T1415, Michal Hocko wrote:
> On Thu 14-12-17 12:44:17, Edward Napierala wrote:
> > Regarding the name - how about adopting MAP_EXCL?  It was introduced in
> > FreeBSD,
> > and seems to do exactly this; quoting mmap(2):
> > 
> > MAP_FIXED    Do not permit the system to select a different address
> >                         than the one specified.  If the specified address
> >                         cannot be used, mmap() will fail.  If MAP_FIXED is
> >                         specified, addr must be a multiple of the page size.
> >                         If MAP_EXCL is not specified, a successful MAP_FIXED
> >                         request replaces any previous mappings for the
> >                         process' pages in the range from addr to addr + len.
> >                         In contrast, if MAP_EXCL is specified, the request
> >                         will fail if a mapping already exists within the
> >                         range.
> 
> I am not familiar with the FreeBSD implementation but from the above it
> looks like MAP_EXCL is a MAP_FIXED mofifier which is not how we are
> going to implement it in linux due to reasons mentioned in this cover
> letter. Using the same name would be more confusing than helpful I am
> afraid.

Sorry, missed that.  Indeed, reusing a name with a different semantics
would be a bad idea.