Michal Hocko <mhocko@xxxxxxxxxx> writes: > [Sorry for spamming, this one is the last attempt hopefully] > > On Mon 13-11-17 16:49:39, Michal Hocko wrote: >> On Mon 13-11-17 16:16:41, Michal Hocko wrote: >> > On Mon 13-11-17 13:00:57, Michal Hocko wrote: >> > [...] >> > > Yes, I have mentioned that in the previous email but the amount of code >> > > would be even larger. Basically every arch which reimplements >> > > arch_get_unmapped_area would have to special case new MAP_FIXED flag to >> > > do vma lookup. >> > >> > It turned out that this might be much more easier than I thought after >> > all. It seems we can really handle that in the common code. This would >> > mean that we are exposing a new functionality to the userspace though. >> > Myabe this would be useful on its own though. Just a quick draft (not >> > even compile tested) whether this makes sense in general. I would be >> > worried about unexpected behavior when somebody set other bit without a >> > good reason and we might fail with ENOMEM for such a call now. >> >> Hmm, the bigger problem would be the backward compatibility actually. We >> would get silent corruptions which is exactly what the flag is trying >> fix. mmap flags handling really sucks. So I guess we would have to make >> the flag internal only :/ > > OK, so this one should take care of the backward compatibility while > still not touching the arch code I'm not sure I understand your worries about backward compatibility? If we add a new mmap flag which is currently unused then what is the problem? Are you worried about user code that accidentally passes that flag already? > diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h > index 203268f9231e..03c518777f83 100644 > --- a/include/uapi/asm-generic/mman-common.h > +++ b/include/uapi/asm-generic/mman-common.h > @@ -25,6 +25,8 @@ > # define MAP_UNINITIALIZED 0x0 /* Don't support this flag */ > #endif > > +#define MAP_FIXED_SAFE 0x2000000 /* MAP_FIXED which doesn't unmap underlying mapping */ > + As I said in my other mail I think this should be a modifier to MAP_FIXED. That way all the existing code that checks for MAP_FIXED (in the kernel) works exactly as it currently does - like the check Khalid pointed out. And I think MAP_NO_CLOBBER would be a better name. cheers -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
