Messages in this thread | | | Date | Mon, 5 Aug 2002 13:17:34 -0700 (PDT) | From | Patrick Mochel <> | Subject | Re: driverfs API Updates |
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On Mon, 5 Aug 2002, Kai Germaschewski wrote:
> On Mon, 5 Aug 2002, Patrick Mochel wrote: > > > [1]: The reason for the macro is because the driverfs internals > > have changed enough to be able to support attributes of any type. In > > order to do this in a type-safe manner, we have a generic object type > > (struct attribute) that we use. We pass this to an intermediate layer > > that does a container_of() on that object to obtain the specific > > attribute type. > > Of course that means that it's not really type-safe, since it has no way > to check whether the object is embedded in the right type of struct, right > ;) (But I think that's okay, C doesn't have provisions for real > inheritance)
Well sure, if you want to get technical. ;) I almost said 'mostly' type-safe, but I decided I would fib a little to make myself sound stronger. Basically, I think it's as safe as we can get, and it was type-safe enough for Linus..
> > This means the specific attribute types have an embedded struct > > attribute in them, making the initializers kinda ugly. I played with > > anonymous structs and unions to have something that could > > theoretically work, but they apparently don't like named > > initializers. > > Have you considered just putting in the embedded part via some macro - > I think that's what NTFS does for compilers which don't support unnamed > structs. > > Basically > > #define EMB_ATTRIBUTE \ > int emb1; > int emb2 > > struct my_attribute { > EMB_ATTRIBUTE > int my1; > int my2; > };
It's not that it's unnamed, it's that we want both object types to exist, and have something to do container_of() on. Yet, have something easy to declare.
I wanted something like:
struct attribute { char * name; mode_t mode; };
struct device_attribute { union { struct attribute attr; struct { char * name; mode_t mode; }; device_show show; device_store store; };
You can access struct device_attribute::name fine, except when using named initializers. At least with gcc 2.96.
> That'll work with named initializers just fine, so the users don't have to > deal with ugly DEVICE_ATTR macros, where one forgets if parameter #3 was > show or store ;) - It follows the common way of hiding away unavoidable > ugliness in some header.
Bah, tradeoffs. It's not that hard to get the parameters right; and it won't take long for them to notice ;)
> > [2]: I wanted to consolidate the first two parameters, but I couldn't > > find a way to stringify ##name (or un-stringify "strname"). Is that > > even possible? > > Why would stringify (include/linux/stringify.h) not work? However, Al Viro > may get mad at you for generating ungreppable symbols either way ;-)
Uhm, because I'm retarded, and I didn't actually try.
-pat
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