[systemd-devel] bind mounts are not delayed until the underlying fs gets mounted

[Andrei Borzenkov]

29.01.2016 17:55, Frank Steiner пишет:
> Hi,
> 
> this problem occurs in SLES 12 with systemd-210-70.30.1 which might be
> to old to handle this situation correctly. So my question is if the
> following situation should work in systemd or for some reason would not
> (so that I can plan how to get around this).
> 
> We have two entries in /etc/fstab:
> 
> /dev/mapper/raid2--iscsi-backup--export /export2        xfs     defaults,_netdev 0 0
> /export2/rpm    /nfsv4/rpm-export       none    bind,private,_netdev 0 0
> 
> I.e., we mount an iscsi device and then export part of it with nfs4,
> so we need the bind-mount. But while both entries are correctly delayed
> due to the _netdev, they both start to mount in parallel and the bind
> mount is faster than the iscsi, of course.
> 
> ...
> [  OK  ] Reached target Remote File Systems (Pre).
> [  OK  ] Reached target Network is Online.
>          Starting Login and scanning of iSCSI devices...
>          Mounting /nfsv4/rpm-export...
> [  OK  ] Mounted /nfsv4/rpm-export.
> [  OK  ] Started Login and scanning of iSCSI devices.
> ...
> [  OK  ] Found device /dev/mapper/raid2--iscsi-backup--export.
> [  OK  ] Started Activation of LVM2 logical volumes.
>          Mounting /export2...
> [  OK  ] Mounted /export2.
> ...
> 
> In http://www.freedesktop.org/software/systemd/man/systemd.mount.html
> I found the information "If a mount unit is beneath another mount unit 
> in the file system hierarchy, both a requirement dependency and an 
> ordering dependency between both units are created automatically."
> 
> This sounds like it should work in the scenario as /export2/rpm is
> clearly beneath /export2. But there are no matching depencendies
> in the the /run/systemd/generator/*.mount files. So is it safe to 
> assume the error only occurs due to the old systemd version?
> 

These dependencies are added internally, they are not found in any
on-disk unit files.

Check with "systemctl show mount-unit".

> In the current release, should this work automatically by adding
> dependencies in the generated mount files or would I have to 
> add "x-systemd.requires-mounts-for" (which my systemd doesn't know 
> about...) explicitely in fstab?
> 

This should work in your version as well. If it does not, the only idea
I have is that /export2/rpm unit is processed before /export2 and so
does not "know" about this dependency yet.