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? It'd be even nicer if it somehow avoided consuming memory when it isn't 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. 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. Thanks Alan -- 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
