> On Dec 17, 2021, at 3:30 AM, David Hildenbrand <david@xxxxxxxxxx> wrote: > > Sometimes it is required to have a seqcount implementation that uses > a structure with a fixed and minimal size -- just a bare unsigned int -- > independent of the kernel configuration. This is especially valuable, when > the raw_ variants of the seqlock function will be used and the additional > lockdep part of the seqcount_t structure remains essentially unused. > > Let's provide a lockdep-free raw_seqcount_t variant that can be used via > the raw functions to have a basic seqlock. > > The target use case is embedding a raw_seqcount_t in the "struct page", > where we really want a minimal size and cannot tolerate a sudden grow of > the seqcount_t structure resulting in a significant "struct page" > increase or even a layout change. > > Provide raw_read_seqcount_retry(), to make it easy to match to > raw_read_seqcount_begin() in the code. > > Let's add a short documentation as well. > > Note: There might be other possible users for raw_seqcount_t where the > lockdep part might be completely unused and just wastes memory -- > essentially any users that only use the raw_ function variants. > Is it possible to force some policy when raw_seqcount_t is used to prevent its abuse? For instance not to allow to acquire other (certain?) locks when it is held? [ snip ] > +/** > + * raw_seqcount_init() - runtime initializer for raw_seqcount_t > + * @s: Pointer to the raw_seqcount_t instance > + */ > +# define raw_seqcount_init(s) __raw_seqcount_init(s) > + > #ifdef CONFIG_DEBUG_LOCK_ALLOC > > # define SEQCOUNT_DEP_MAP_INIT(lockname) \ > @@ -111,11 +129,16 @@ static inline void seqcount_lockdep_reader_access(const seqcount_t *s) > # define seqcount_lockdep_reader_access(x) > #endif > > +/** > + * RAW_SEQCNT_ZERO() - static initializer for raw_seqcount_t > + */ > +#define RAW_SEQCNT_ZERO() 0 I am not sure why RAW_SWQCNT_ZERO() should be a function-like macro. Moreover, the documentation showed: + /* static */ + static raw_seqcount_t foo_seqcount = RAW_SEQCNT_ZERO(foo_seqcount); + But RAW_SEQCNT_ZERO does not have an argument?
