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a=-5_ipbWy7f3QC6ut6rwA:9 a=CjuIK1q_8ugA:10 a=-El7cUbtino8hM1DCn8D:22 cc=ntf awl=host:13602 On Wed, Aug 27, 2025 at 02:48:32PM -0700, Andrew Morton wrote: > On Wed, 27 Aug 2025 21:22:33 +0200 Max Kellermann wrote: > > > For improved const-correctness. > > OK... > > > > > --- a/include/linux/fs.h > > +++ b/include/linux/fs.h > > @@ -537,7 +537,7 @@ struct address_space { > > /* > > * Returns true if any of the pages in the mapping are marked with the tag. > > */ > > -static inline bool mapping_tagged(struct address_space *mapping, xa_mark_t tag) > > +static inline bool mapping_tagged(const struct address_space *mapping, xa_mark_t tag) > > { > > return xa_marked(&mapping->i_pages, tag); > > } > > I'd actually be in favor of making all incoming args const (C should > have made this the default). > > Because modifying an incoming arg is just obnoxious. That value should > be viewed as part of the calling environment and should not be altered. > > Try modifying a lengthy function and wanting to get at an incoming arg > only to find that something in the preceding 100 lines has gone and > messed with it. Or forget to check fr this and get a nasty surprise when > testing. > > Not that I'm suggesting that someone go in and make this change. > > On the other hand, it would be neat if gcc had an option to warn when > someone does this. I bet it would be simple to add. This would break half the world, I've tried making parameters const, then finding basically every helper function doesn't function correctly with it + having to give up without needing to change half the code base. It's kind of a dominoes thing at this point. Broadly I'm in agreement that 'const by default' is good, but there's quite a big price to pay for this in terms of changes needed for really quite dubious gains. I think perhaps 'const if we can moving forward' is better. Also note that C 'const' is _extremely_ weak. So it's more of a 'readonly kinda'.