Messages in this thread | | | Date | Tue, 22 Dec 2020 13:44:38 +0000 | From | Christoph Hellwig <> | Subject | Re: [PATCH 1/2] mm/madvise: allow process_madvise operations on entire memory range |
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On Fri, Dec 11, 2020 at 09:27:46PM +0100, Jann Horn wrote: > > Can we just use one element in iovec to indicate entire address rather > > than using up the reserved flags? > > > > struct iovec { > > .iov_base = NULL, > > .iov_len = (~(size_t)0), > > }; > > In addition to Suren's objections, I think it's also worth considering > how this looks in terms of compat API. If a compat process does > process_madvise() on another compat process, it would be specifying > the maximum 32-bit number, rather than the maximum 64-bit number, so > you'd need special code to catch that case, which would be ugly. > > And when a compat process uses this API on a non-compat process, it > semantically gets really weird: The actual address range covered would > be larger than the address range specified. > > And if we want different access checks for the two flavors in the > future, gating that different behavior on special values in the iovec > would feel too magical to me. > > And the length value SIZE_MAX doesn't really make sense anyway because > the length of the whole address space would be SIZE_MAX+1, which you > can't express. > > So I'm in favor of a new flag, and strongly against using SIZE_MAX as > a magic number here.
Yes, using SIZE_MAX is a horrible interface in this case. I'm not a huge fan of a flag either. What is the use case for the madvise to all of a processes address space anyway?
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