Messages in this thread | | | Date | Fri, 30 Nov 2007 13:04:20 -0800 | From | Greg KH <> | Subject | Re: [RFC] kobject: add kobject_init_ng and kobject_init_and_add functions |
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On Fri, Nov 30, 2007 at 03:25:52PM -0500, Alan Stern wrote: > On Fri, 30 Nov 2007, Greg KH wrote: > > > +/** > > + * kobject_init_and_add - initialize a kobject structure and add it to the kobject hierarchy > > + * @kobj: pointer to the kobject to initialize > > + * @ktype: pointer to the ktype for this kobject. > > + * @parent: pointer to the parent of this kobject. > > + * @fmt: the name of the kobject. > > + * > > + * This function will properly initialize a kobject and then call > > + * kobject_add(). > > + * > > + * If the function returns an error, the memory allocated by the kobject > > + * can be safely freed, no other functions need to be called. > > + */ > > +int kobject_init_and_add(struct kobject *kobj, struct kobj_type *ktype, > > + struct kobject *parent, const char *fmt, ...) > > +{ > > + va_list args; > > + int retval; > > + > > + va_start(args, fmt); > > + retval = kobject_init_varg(kobj, ktype, parent, fmt, args); > > + va_end(args); > > + if (retval) > > + return retval; > > + > > + retval = kobject_add(kobj); > > + if (retval) > > + kobject_put(kobj); > > No, no! > > You have recreated the problem we have been discussing during the last > couple of days. If the kobject_init_varg() routine gets an error then > the kobject will need to be deallocated manually. If the kobject_add() > routine gets an error then the cleanup invoked by kobject_put() will do > the deallocation automatically. > > But the caller can't tell in which subroutine an error occurred, so it > won't know what to do when kobject_init_and_add() returns an error.
Oh crap. You're totally right. I suck.
> The only way to resolve this problem is to have the _init routine > consume no resources and never fail. That way the only possible > failure mode would be if the _add routine doesn't work, in which case > either a kfree() or a kobject_put() would be acceptable. > > In particular, this implies that the name should be set as part of the > _add() call, not as part of _init(). This is more in line with the way > the code tends to use kobjects anyhow. Unless people want to name > unregistered kobjects -- does this ever happen? And it if does, can > these kobjects simply be replaced by krefs?
No, the only non-registered kobjects in the tree right now are never named. So this should be safe.
> My suggestion: Have kobject_init_ng() accept a ktype pointer but not a > parent or name. Instead, make kobject_add_ng() take the parent and > name (possibly a kset also). Then when kobject_init_and_add() > encounters an error, it shouldn't do a _put() -- the caller can either > do the _put() or just do a kfree().
Why not the parent for init()? Isn't it always known at that time? I'll dig to be sure.
Ok, second round of patches coming up...
thanks,
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