Mounting legacy dataset gives cryptic error messages

[ryao]

Attempting to mount a legacy dataset on a non-existent mount point will give a numerical error message:

vserver ~ # zfs create rpool/backup/www
vserver ~ # mount -t zfs rpool/backup/www /mnt/backup/www
filesystem 'rpool/backup/www' can not be mounted due to error 2
vserver ~ # mkdir /mnt/backup/www
vserver ~ # mount -t zfs rpool/backup/www /mnt/backup/www
vserver ~ # zfs list rpool/backup
NAME USED AVAIL REFER MOUNTPOINT
rpool/backup 409G 5.02T 409G legacy

I am not sure if this is an issue that we can address, but I thought I would report it so others can take a look.

[behlendorf]

We can certainly do something about this. The error is coming from our mount.zfs helper. What would you expect correct behavior to be?

cmd/mount_zfs/mount_zfs.c:478

        if (!fake) {
                error = mount(dataset, mntpoint, MNTTYPE_ZFS,
                    mntflags, mntopts);
                if (error) {
                        switch (errno) {
                        case EBUSY:
                                (void) fprintf(stderr, gettext("filesystem "
                                    "'%s' is already mounted\n"), dataset);
                                return (MOUNT_SYSERR);
                        default:
                                (void) fprintf(stderr, gettext("filesystem "
                                    "'%s' can not be mounted due to error "
                                    "%d\n"), dataset, errno);
                                return (MOUNT_USAGE);
                        }
                }
        }

[ryao]

I will patch this and then file a pull request when a patch is ready.

[skull-squadron]

Thanks for fixing this. Just ran into it on 0.6.0-rc8.