On 11/25/2017 07:45 PM, Helge Deller wrote:
On 22.11.2017 20:53, Matthew Wilcox wrote:
> On Wed, Nov 22, 2017 at 08:52:37AM -0800, Dan Williams wrote:
>> On Wed, Nov 22, 2017 at 4:02 AM, Vlastimil Babka <vbabka(a)suse.cz> wrote:
>>> On 11/01/2017 04:36 PM, Jan Kara wrote:
>>>> From: Dan Williams <dan.j.williams(a)intel.com>
>>>> The mmap(2) syscall suffers from the ABI anti-pattern of not validating
>>>> unknown flags. However, proposals like MAP_SYNC need a mechanism to
>>>> define new behavior that is known to fail on older kernels without the
>>>> support. Define a new MAP_SHARED_VALIDATE flag pattern that is
>>>> guaranteed to fail on all legacy mmap implementations.
>>> So I'm trying to make sense of this together with Michal's attempt
>>> MAP_FIXED_SAFE  where he has to introduce a completely new flag
>>> instead of flag modifier exactly for the reason of not validating
>>> unknown flags. And my conclusion is that because MAP_SHARED_VALIDATE
>>> implies MAP_SHARED and excludes MAP_PRIVATE, MAP_FIXED_SAFE as a
>>> modifier cannot build on top of this. Wouldn't thus it be really better
>>> long-term to introduce mmap3 at this point? ...
>> We have room to define MAP_PRIVATE_VALIDATE in MAP_TYPE on every arch
>> except parisc. Can we steal an extra bit for MAP_TYPE from somewhere
>> else on parisc?
> It looks like 0x08 should work.
I posted an RFC to the parisc mailing list for that:
Thanks. BTW there doesn't seem to be much interest making MAP_FIXED_SAFE
a flag modifier after all, so MAP_PRIVATE_VALIDATE wouldn't get
Basically this is (for parisc only):
-#define MAP_TYPE 0x03 /* Mask for type of mapping */
+#define MAP_TYPE (MAP_SHARED|MAP_PRIVATE|MAP_RESRVD1|MAP_RESRVD2) /* Mask for type of
#define MAP_FIXED 0x04 /* Interpret addr exactly */
+#define MAP_RESRVD1 0x08 /* reserved for 3rd bit of MAP_TYPE */
#define MAP_ANONYMOUS 0x10 /* don't use a file */
+#define MAP_RESRVD2 0x20 /* reserved for 4th bit of MAP_TYPE */
> But I don't have an HPUX machine around
> to check that HP didn't use that bit for something else.
We completely dropped support for HPUX binaries, so it's not relvant any longer.
> It'd probably help to cc the linux-parisc mailing list when asking
> questions about PARISC, eh?