On Tue, Nov 25, 2008 at 01:08:09AM +0900, Tejun Heo wrote: > Devices can be killed from userland via sysfs for SCSI or mdadm for > md. It's true that such approach is less convenient for unloading but > if it can make usual cases easier, why not? _What_ usual cases? > > And the right way to deal with that is to have explicit boundaries for > > "opened or in process of being opened"; we almost have them (probe and > > final release), so the only point we are missing is on failure exit from > > __blkdev_get()... > > > > I really think that it's much saner than trying to change the lifetime > > rules for gendisk, etc. > > Well, I don't know. It seems like a lot of trouble just to allow > "rmmod something" without first killing the devices and as people are > now so used to reference counted objects and ->release, not having it > on cdev or gendisk is quite a PITA. (BTW, Greg, can you please drop > cdev->release patch for now, it's wrong as it currently stands). gendisks *ARE* reference counted, damnit. So are net_device and a lot of other things. And no, it's not true that "struct net_device exists" implies "the low-level objects that once might have been related to it still exist" either. > Can you see any problem with caching ->disk_release existence on > registration and wrap __module_get/put() around its invocation? It > wouldn't change behavior of any existing drivers and md can use it if > it wants. Doing "mdadm --stop --scan" would be enough to unload the > module and md can do whatever forward or back reference it wants to do > to work out the weird userland interface. Other than general ugliness and special-casing where none is really needed? Special-casing as "very different life cycle if special method is present"... If anything, we need to go in opposite direction - give the drivers a way to say "my underlying object is gone, STFU and don't bother me with that gendisk ever again; free it when you are done with it, but from now on any access to it would better fail. Oh, and I might find a new device in place of that any time now, so new open() would better get not fail just something in VFS still has a reference to that gendisk". Which is doable - note that we can unhash block_device, dissociate inodes from it and let new open() DTRT. Earlier opened files will still have a reference to address_space of original block_device (which is why we have file->f_mapping instead of going through ->f_dentry->d_inode->i_mapping), so we are fine. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
