zfsd(8): Close a race condition when onlining a disk paritition

[asomers]

Summary

zfsd(8): Close a race condition when onlining a disk paritition

When inserting a partitioned disk, devfs and geom will announce the whole
disk before they announce the partition. If the partition containing ZFS
extends to one of the disk's extents, then zfsd will see a ZFS label on the
whole disk and attempt to online it. ZFS is smart enough to activate the
partition instead of the whole disk, but only if GEOM has already created
the partition's provider.

cddl/contrib/opensolaris/lib/libzfs/common/libzfs.h
cddl/contrib/opensolaris/lib/libzfs/common/libzfs_import.c
Add a zpool_read_all_labels method. It's similar to
zpool_read_label, but it will return the number of labels found.

cddl/usr.sbin/zfsd/zfsd_event.cc
When processing a DevFS CREATE event, only online a VDEV if we can
read all four ZFS labels.

[mav]

You haven't included zpool_read_all_labels method into the patch.

I don't have objections other then ones I sounded when you implemented alike functionality in kernel.

[asomers]

Whoops! Here's zpool_read_all_labels

[asomers]

In D11920#247428, @mav wrote:

I don't have objections other then ones I sounded when you implemented alike functionality in kernel.

Presumably you mean D10365. I agree that this seems like a hackish way to verify that we're reading the correct partition. But the label doesn't include the size of the device, so I don't see what other option there is. Adding mediasize to the label would be a change to the ZFS on-disk format, albeit a backwards-compatible one.