Messages in this thread | | | From | Kay Sievers <> | Date | Tue, 7 Feb 2012 11:05:42 +0100 | Subject | Re: No /dev/root with devtmpfs? |
| |
On Tue, Feb 7, 2012 at 08:55, Kirill Smelkov <kirr@mns.spb.ru> wrote: > On Mon, Feb 06, 2012 at 08:45:24PM +0100, Kay Sievers wrote: >> On Mon, Feb 6, 2012 at 12:18, Kirill Smelkov <kirr@mns.spb.ru> wrote: >> > Recently I've reworked my system not to use udev, but use devtmpfs >> > instead and discovered there is no /dev/root symlink in devtmpfs case. >> > >> > My setup uses /dev/root early to know what is the boot device and then >> > do some operations on it like checksumming, etc... >> > >> > Now when /dev/root is gone the best workaround I could come up with is >> > to grep /proc/partitions for '[hs]d[a-z]1' but it's ugly and will >> > break when there are several block devices attached. >> > >> > Is it somehow possible to add /dev/root to devtmpfs? >> >> No, devtmpfs has no business in knowing anything about the rootfs or >> who mounted what ans where. I can not create such links. >> >> The entire concept of /dev/root is flawed anyway, and nothing should >> really depend on that. >> >> Modern filesystems will not offer a direct relation to a single block >> device, they allocate an superblock which has a major == 0, so there >> can be by definition never such a link. Better get rid of all uses of >> /dev/root, it will just fail in the future. > > Kay, thanks for explanation. > > Though now I'm confused about how to know on what "place" root > filesystem was mounted... To me the question makes sense, but you say > with modern filesystems there by definition is no answer (or did I > misunderstood you?) Strange...
The root filesystem will still be mounted at /, but you can not identify by a device. Check the difference between: $ mountpoint -d / 8:1 which is a classic ext4 sda1 device behind "/".
With 'btrfs' it will just look like 'tmpfs' looks today: $ mountpoint -d /dev/shm 0:17
and while the 'btrfs' file system is surely backed by a disk/partition, just like ext4 is, there can still never be a symlink to the disk device.
Tools need to work without in the future without having a /dev/root symlink
Kay -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |