Messages in this thread | | | Date | Fri, 30 Nov 2007 15:25:52 -0500 (EST) | From | Alan Stern <> | Subject | Re: [RFC] kobject: add kobject_init_ng and kobject_init_and_add functions |
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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.
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?
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().
Alan Stern
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