On Thu, 2010-12-23 at 12:12 +0100, Lennart Poettering wrote: > On Wed, 22.12.10 22:38, Bernie Innocenti (bernie@xxxxxxxxxxx) wrote: > > > What's preventing us from symlinking /etc/mtab to /proc/mounts and get > > rid of confusing situations when mtab gets out of sync with the > > kernel? > > Some of the mount options that /bin/mount uses currently are seen by > userspace only and cannot be attached to the mount point in-kernel. The > effect of that is that if you symlink /etc/mtab to /proc/mounts these > options get silently dropped after mount, and while they might have > effect at mount time, afterwards (i.e. umount time) they will have zero > effect. An example of such an option is "user" and "users". > > It is definitely planned to get rid of /etc/mtab, but before that > happens the kernel must either learn to store userspace mount options > along kernel mount options for each mount point in some way (Miklos > Szeredi has been working on this IIRC), or /bin/mount must learn to > store these options somewhere in userspace (for example /dev/.mount or > so), and then augment its output with these options. (Karel Zak has been > thinking about adding this). And lets not forget the need for a pseudo mount option that can be used by the user space tools to ignore certain mounts, such as autofs mounts. > > Sooner or laer we will definitely make /etc/mtab a symlink, which should > take us one definite step nearer to supporting r/o root by default. > > In fact, in systemd we already warn during boot if /etc/mtab is not a > symlink, and we do not longer clear that file on bootup, all to put a > tiny bit of pressure on the folks involved to fix this properly once and > for all, in the F15 timeframe... > > > I tried running my system for a few months this way. The only > > regressions I'm seeing are: > > > > 1) the Gnome Disk Mounter panel applet seems to get confused. After a > > loopback mount gets unmounted, there's still an icon to remount the > > device. (the loopback device is correctly cleaned up at umount time). > > Loop devices use userspace-only mount options too, afair. > > > 2) on boot, the system tries to remount /sys even though it's already > > mounted, thus spitting this harmless error: > > > > Remounting root filesystem in read-write mode: [ OK ] > > mount: according to mtab, /dev/sda1 is already mounted on / > > Mounting local filesystems: mount: sysfs already mounted or /sys busy > > mount: according to mtab, /sys is already mounted on /sys [FAILED] > > Enabling /etc/fstab swaps: [ OK ] > > This problem is gone on F15/Rawhide anyway, since systemd mounts this dir. > > Lennart > > -- > Lennart Poettering - Red Hat, Inc. -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel
