Messages in this thread | | | Date | Wed, 27 Dec 2017 13:18:34 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH v5 03/78] xarray: Add the xa_lock to the radix_tree_root |
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On Tue, Dec 26, 2017 at 07:58:15PM -0800, Matthew Wilcox wrote: > 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
Yeah, that's neat.
Dealing with old compilers is frustrating...
-- Kirill A. Shutemov
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