On Tue, Dec 26, 2017 at 07:43:40PM -0800, Matthew Wilcox wrote:
> Also add the xa_lock() and xa_unlock() family of wrappers to make it
> easier to use the lock. If we could rely on -fplan9-extensions in
> the compiler, we could avoid all of this syntactic sugar, but that
> wasn't added until gcc 4.6.
Oh, in case anyone's wondering, here's how I'd do it with plan9 extensions:
struct xarray {
spinlock_t;
int xa_flags;
void *xa_head;
};
...
spin_lock_irqsave(&mapping->pages, flags);
__delete_from_page_cache(page, NULL);
spin_unlock_irqrestore(&mapping->pages, flags);
...
The plan9 extensions permit passing a pointer to a struct which has an
unnamed element to a function which is expecting a pointer to the type
of that element. The compiler does any necessary arithmetic to produce
a pointer. It's exactly as if I had written:
spin_lock_irqsave(&mapping->pages.xa_lock, flags);
__delete_from_page_cache(page, NULL);
spin_unlock_irqrestore(&mapping->pages.xa_lock, flags);
More details here: https://9p.io/sys/doc/compiler.html
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