mount on non-emtpy mountpoint: default -O for 'zfs mount'

[GregorKopka]

2nd bullet here: #274

Currently i can't create a dataset (update: not a zvol) covering /etc/dfs since every zfs and zpool command touches the sharetab in there, so even when i clear out the contents of the directory is repopulated the moment i issue an zfs command (like 'mount tank/etc/dfs').

The reason for me wanting to put /etc/dfs into a zfs dataset (update: not a zvol) is that the rootfs is on flash memory and the only thing which is left writing to / after boot is complete are the constant updates zfs does to /etc/dfs/sharetab - reducing the lifetime of the flash stick.

Can -O made be default for 'zfs mount' please ?

[ryao]

I believe that Solaris does not permit mounting on non-empty mount points, so I don't think that this is appropriate change to make. I think that your issue can be resolved by putting /etc/dfs on a tmpfs.

Add an entry like tmpfs /etc/dfs tmpfs size=32M,nosuid 0 0 to /etc/fstab, do rm /etc/dfs/sharetab and reboot. If that does not work, you might need to delete that file from a rescue environment.

[GregorKopka]

Already did the the tmpfs mount, which - since it's on linux - didn't care that /etc/dfs isn't empty.

Surely a difficult decision to make, but since it's zfsonlinux (and not solarisonlinux) i sounds reasonable to me to not break the linux way of mounting filesystems.

I opened this to get a discussion rolling about how to deal with the situation. Any comments from others?

[ryao]

@GregorKopka Does zfs mount apply to zvols?

If this involved a dataset, I would suggest setting mountpoint=legacy, but I am somewhat confused after taking another look at this and realizing that it involves zvols.

[GregorKopka]

/me stupid, i ment dataset. Sorry for the confusion. Updated original post.

[ryao]

Have you tried setting mountpoint=legacy and using /etc/fstab to mount it? That should do what you want.

[behlendorf]

The root cause of this issue should be resolved by commit 27ccd41 . The /etc/dfs/sharetab file will now only be touched when your performing some NFS related operation.