Messages in this thread | | | Date | Wed, 7 Jan 2004 11:50:33 -0800 | From | Greg KH <> | Subject | Re: removable media revalidation - udev vs. devfs or static /dev |
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On Wed, Jan 07, 2004 at 11:31:55AM -0800, Linus Torvalds wrote: > On Wed, 7 Jan 2004, Greg KH wrote: > > > But udev should probably also create all the sub-nodes if it doesn't > > > already. > > > > It doesn't, as I thought we could rely on the kernel partition support. > > Indeed, we _can_ rely on the kernel partition support, but the subnodes > are needed to get at those partitions. > > Obviously, a "repartitioning hotplug event" can create the subnodes, but > that will fail exactly because it wouldn't allow the user to just access > the nodes.
It sounds like just having the device node around will not cause the rescan if you access it. I don't have any such devices here to test this out or not. If true, having udev create all nodes will not help out much :(
> > Hm, that would work, but what about a user program that just polls on > > the device, as the rest of this thread discusses? > > I hate those "background CPU users". Have you looked at "ps" output after > something like kscd has run, and does a CD check every second? It's > _expensive_. It goes all the way down to the hardware, sends a request > to the device.
Oh I know, it's one of the first things I disable when setting up a box :)
> Doing it every five minutes wouldn't be an issue, but doing it every five > minutes would be absolutely _horrible_ from a user perspective standpoint. > If you insert a smartmedia card in your cardreader, you expect to be able > to access it pretty much immediately when you start typing. So a second or > two of delay is fine, but even just five or ten seconds are already bad. > > So the choice is: > - probe every removable device once a second > - pre-populate the device nodes, and when the user presses the icon that > says "mount", it will just do so. Immediately. No delay at all.
Based on the previous info, I think we are stuck with probing :(
> NOTE! We do have an alternative: if we were to just make block device > nodes support "readdir" and "lookup", you could just do > > open("/dev/sda/1" ...) > > and it magically works right. I've wanted to do this for a long time, but > every time I suggest allowing it, people scream.
Hm, that would be nice. I don't remember seeing it being proposed before, what are the main complaints people have with this?
thanks,
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