At last a useful user space interface for the Linux ZFS port arrives.
With the addition of the ZVOL real ZFS based block devices are available
and can be compared head to head with Linux's MD and LVM block drivers.
The Linux ZVOL has not yet had any performance work done but from a user
perspective it should be functionally complete and behave like any other
Linux block device.
The ZVOL has so far been tested using zconfig.sh on the following x86_64
based platforms: FC11, CHAOS4, RHEL5, RHEL6, and SLES11. However, more
testing is required to ensure everything is working as designed.
What follows in a somewhat detailed list of changes includes in this
commit to make ZVOL's possible. A few other issues were addressed in
the context of these changes which will also be mentioned.
* zvol_create_link_common() simplified to simply issue to ioctl to
create the device and then wait up to 10 seconds for it to appear.
The device will be created within a few miliseconds by udev under
/dev/<pool>/<volume>. Note this naming convention is slightly
different than on Solaris by I feel is more Linuxy.
* Removed support for dump vdevs. This concept is specific to Solaris
and done not map cleanly to Linux. Under Linux generating system cores
is perferably done over the network via netdump, or alternately to a
block device via O_DIRECT.
The majority of this this patch concerns itself with doing a direct
replacement of Solaris's libdiskmgt library with libblkid+libefi.
You'll notice that this patch removes all libdiskmgt code instead of
ifdef'ing it out. This was done to minimize any confusion when reading
the code because it seems unlikely we will ever port libdiskmgt to Linux.
Despite the replacement the behavior of the tools should have remained
the same with one exception. For the moment, we are unable to check
the partitions of devices which have an MBR style partition table when
creating a filesystem. If a non-efi partition sceme is detected on a
whole disk device we prompt the user to explicity use the force option.
It would not be a ton of work to make the tool aware of MBR style
partitions if this becomes a problem.
I've done basic sanity checking for various configurations and all
the issues I'm aware of have been addressed. Even things like blkid
misidentifing a disk as ext3 when it is added to a zfs pool. I'm
careful to always zero out the first 4k of any new zfs partition. That
all said this is all new code and while it looks like it's working right
for me we should keep an eye on it for any strange behavior.
Most of these fixes appear to be harmless and should never occur.
However, there were a few cases in this patch which do concern me,
I doubt we're seeing them but they look possible... mainly in the
user tools.
Brian Behlendorf