Greg KH a écrit : > On Sun, Jan 29, 2006 at 02:58:51PM -0700, Eric W. Biederman wrote: >> Greg KH writes: >> >>> On Sun, Jan 29, 2006 at 12:22:34AM -0700, Eric W. Biederman wrote: >>>> +struct task_ref >>>> +{ >>>> + atomic_t count; >>> Please use a struct kref here, instead of your own atomic_t, as that's >>> why it is in the kernel :) >>> >>>> + enum pid_type type; >>>> + struct task_struct *task; >>>> +}; >>> thanks, >> I would rather not. Whenever I look at struct kref it seems to be an over >> abstraction, and as such I find it confusing to work with. I know >> whenever I look at the sysfs code I have to actively remind myself >> that the kref in the structure is not a pointer to a kref. >> >> What does the kref abstraction buy? How does it simplify things? >> We already have equivalent functions in atomic_t on which it is built. > > It ensures that you get the logic of the reference counting correctly. > It forces you to do the logic of the get and put and release properly. > > To roughly quote Andrew Morton, "When I see a kref, I know it is used > properly, otherwise I am forced to read through the code to see if the > author got the reference counting logic correct." > > It costs _nothing_ to use it, and let's everyone know you got the logic > correct. > > So don't feel it is a "abstraction", it's a helper for both the author > (who doesn't have to get the atomic_t calls correct), and for everyone > else who has to read the code. > kref abstraction is good. Its current implementation seems straightforward, so I understand some devs think they can 'just use an atomic_t' themselves. But using kref is better because some generic improvement could be done at kref level and you dont need to parse all kernel sources to change atomic_t to kref... Example of improvement in kref_put() : [PATCH] kref : Avoid an atomic operation in kref_put() when the last reference is dropped. On most platforms, atomic_read() is a plan read of the counter and involves no atomic at all. Signed-off-by: Eric Dumazet