On Sat, May 2, 2009 at 23:41, Alan Jenkins <sourcejedi.lkml@xxxxxxxxxxxxxx> wrote: > On 5/2/09, Alan Jenkins <sourcejedi.lkml@xxxxxxxxxxxxxx> wrote: >> On 5/2/09, Kay Sievers <kay.sievers@xxxxxxxx> wrote: >>> On Sat, May 2, 2009 at 09:16, Christoph Hellwig <hch@xxxxxxxxxxxxx> >>> wrote: >>>> >After the rootfs is mounted by the kernel, the >>>>> populated tmpfs is mounted at /dev. In initramfs, it can be moved >>>>> to the manually mounted root filesystem before /sbin/init is >>>>> executed. >>>> >>>> That for example is something that is not acceptable. We really don't >>>> want the kernel to mess with the initial namespace in such a major way. >>> >>> There is nothing like "mess around", it's not mounted at all, until >>> the kernel mounts the root filesystem at /, then devtmpfs is mounted >>> the first time, and only if it's compiled in because you asked for it. >>> Also, just try: >>> egrep 'mknod|create_dev' init/*.c >>> and see what we currently do. >>> >>>> Counter-proposal: Re-introduce a proper mini-devfs. All nodes in there >>>> are kernel-created and not changeable which sorts out that whole >>>> mess of both drivers and userspace messing with tree topology we had >>>> both in original devfs and this new devtmpfs. Single-instance so it can >>>> be >>>> populated before it's actually mounted somewhere, that way the kernel >>>> doesn't have to do any policy devicision on where it's mounted. >>> >>> That sounds worse than devtpfs, and does not help for most of the >>> mentioned problems we are trying to solve here. >> >> On a narrow issue: do you really object to moving the "mount dev -t >> devfs2 /dev" into userspace (and therefore giving it a user-visible >> name)?? That would address Cristophs particular objection about >> "messing around" with the initial namespace. It means I can be 100% >> sure I can boot an old initramfs with this option enabled. And it >> gives a nice clean way for new initramfs' to test for this feature - >> when they try to mount it, it fails. It would seem to make for a >> rather smoother migration path. >> >> It shouldn't mean too many more LOC, you're already doing the "single >> instance" thing. > > Also, AFAICS this would avoid a memory leak on umount. > > In it's original form, if you unmount it, you can't get it back. But > it doesn't get destroyed either; all the tmpfs nodes just hang around > in limbo, right? Sure you can't get it back if you drop it, but what would be the point of un-mounting it and wanting it back? It's just like every other tmpfs too. :) > It'd be even nicer if it somehow avoided consuming memory when it > isn't used. It's probably easy to make it destroy itself, and free everything, if it's un-mounted, if that solves your concerns about built-in but not used. > I guess that requires more code, looks more like a "real" > devfs, and as C. says is probably more sane if exported as a read > only. Hopefully it would make it possible to remove the code > afterwards, but that sounds like even more work. Then you should probably not enable it, or have a boot option to disable it. What's the point in removing it later, it is exactly what you want, and what everybody has today, a /dev on tmpfs, just that the kernel will puts the default nodes in there. > But is read-only so bad? You just have to copy it over to a tmpfs and > then mount that on top of /dev. That's atomic, so it won't interfere > with parallel early init. I sympathize, devtmpfs is a really neat > hack that does exactly what udev needs. But you have to admit, it > doesn't fit in _quite_ as well with the kernel status quo. I think it fits quite nice as a "device node companion" to sysfs. And I don't really see the point of a read-only mount, it should be the /dev that is used on the real system, until you shut it down. Thanks, Kay -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
