On Sat, 11 Jun 2011, Hans de Goede wrote: > >> So what do we need to make this situation better: > >> 1) A usb_driver callback alternative to the disconnect callback, > >> I propose to call this soft_disconnect. This serves 2 purposes > >> a) It will allow the driver to tell the caller that that is not > >> a good idea by returning an error code (think usb mass storage > >> driver and mounted filesystem > > > > Not feasible. usb-storage has no idea whether or not a device it > > controls has a mounted filesystem. (All it does is send SCSI commands > > to a device and get back the results.) Since that's the main use > > case you're interested in, this part of the proposal seems destined to > > fail. > > > > This is not completely true, I cannot rmmod usb-storage as long as > disks using it are mounted. I know this is done through the global > module usage count, so this is not per usb-storage device. But extending > the ref counting to be per usb-storage device should not be hard. > > All the accounting is already done for this.
It would be harder than you think. All the accounting is _not_ already being done. What you're talking about would amount to a significant change in the driver model core and the SCSI core. It isn't just a USB thing. > > But userspace _does_ know where the mounted filesystems are. > > Therefore userspace should be responsible for avoiding programs that > > want to take control of devices holding these filesystems. That's the > > reason why usbfs device nodes are owned by root and have 0644 mode; > > there're can be written to only by programs with superuser privileges > > -- and such programs are supposed to be careful about what they do. > > > > Yes, and what I'm asking for is for an easy way for these programs to > be careful. A way for them to ask the kernel, which in general is > responsible for things like this and traditionally does resource > management and things which come with that like refcounting: "unbind > the driver from this device unless the device is currently in use". Sure. At the moment the kernel does not keep track of whether a device is currently in use -- at least, not in the way you mean. I'm not saying this can't be done. But it would be a bigger job than you think, and this isn't the appropriate thread to discuss it. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
