With the update to onnv_141 how minor devices were created and
removed for ZVOL was substantially changed. The updated system
is much more tightly integrated with Solaris's /dev/ filesystem.
This is great for Solaris but bad for Linux.
This patch keeps as much of those changes as possible which as
useful for Linux. But it also reverts back to use the old system
of explicit minor node creation via a decicated ioctl(). This
worked well in zfs-0.4.9 and it should continue to work well.
Solaris recently introduced the idea of drive topology because
where a drive is located does matter. I have already handled
this with udev/blkid integration under Linux so I'm hopeful
this case can simply be removed but for now I've just stubbed
out what is needed in libspl and commented out the rest here.
This topic branch leverages the Solaris style FMA call points
in ZFS to create a user space visible event notification system
under Linux. This new system is called zevent and it unifies
all previous Solaris style ereports and sysevent notifications.
Under this Linux specific scheme when a sysevent or ereport event
occurs an nvlist describing the event is created which looks almost
exactly like a Solaris ereport. These events are queued up in the
kernel when they occur and conditionally logged to the console.
It is then up to a user space application to consume the events
and do whatever it likes with them.
To make this possible the existing /dev/zfs ABI has been extended
with two new ioctls which behave as follows.
* ZFS_IOC_EVENTS_NEXT
Get the next pending event. The kernel will keep track of the last
event consumed by the file descriptor and provide the next one if
available. If no new events are available the ioctl() will block
waiting for the next event. This ioctl may also be called in a
non-blocking mode by setting zc.zc_guid = ZEVENT_NONBLOCK. In the
non-blocking case if no events are available ENOENT will be returned.
It is possible that ESHUTDOWN will be returned if the ioctl() is
called while module unloading is in progress. And finally ENOMEM
may occur if the provided nvlist buffer is not large enough to
contain the entire event.
* ZFS_IOC_EVENTS_CLEAR
Clear are events queued by the kernel. The kernel will keep a fairly
large number of recent events queued, use this ioctl to clear the
in kernel list. This will effect all user space processes consuming
events.
The zpool command has been extended to use this events ABI with the
'events' subcommand. You may run 'zpool events -v' to output a
verbose log of all recent events. This is very similar to the
Solaris 'fmdump -ev' command with the key difference being it also
includes what would be considered sysevents under Solaris. You
may also run in follow mode with the '-f' option. To clear the
in kernel event queue use the '-c' option.
$ sudo cmd/zpool/zpool events -fv
TIME CLASS
May 13 2010 16:31:15.777711000 ereport.fs.zfs.config.sync
class = "ereport.fs.zfs.config.sync"
ena = 0x40982b7897700001
detector = (embedded nvlist)
version = 0x0
scheme = "zfs"
pool = 0xed976600de75dfa6
(end detector)
time = 0x4bec8bc3 0x2e5aed98
pool = "zpios"
pool_guid = 0xed976600de75dfa6
pool_context = 0x0
While the 'zpool events' command is handy for interactive debugging
it is not expected to be the primary consumer of zevents. This ABI
was primarily added to facilitate the addition of a user space
monitoring daemon. This daemon would consume all events posted by
the kernel and based on the type of event perform an action. For
most events simply forwarding them on to syslog is likely enough.
But this interface also cleanly allows for more sophisticated
actions to be taken such as generating an email for a failed drive
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.
When creating partition tables we always need to wait until not
only the /dev/<disk><part> device appears. But just as importantly
if we were originally given a udev path we need to wait for the
/dev/disk/*/<name>-part<part> symlink to be created. However,
since the partition naming convention differs between /dev/ and
/dev/disk we determine based on the path which convention to
expect and then wait (for a few seconds) for the device to be
created. Based on my experience with udev on my test nodes it
takes about 300ms for the devices to be created after being
prompted by the kernel. This time will vary somehwat based
on how complicated your udev rules are, so for safety I threw
in a factor of 10. We wait 3 seconds for the devices to appears
before erroring out with a failure.
An additional minor fix includes checking the force flag in the
EFI_GPT_PRIMARY_CORRUPT case. This allows you to force the
update even in the corrupt partition case.
Finally, since these are Linux only changes I've dropped the
devid code entirely here because I still can't think of why we
would need or want it on a Linux system.
The major change here is to fix up libefi to be linux aware. For
the most part this wasn't too hard but there were a few major issues.
First off I needed to handle the DKIOCGMEDIAINFO and DKIOCINFO ioctls.
There is no direct equivilant for these ioctls under linux. To handle
this I added wrapper functions which under Solaris simple call the ioctls.
But under Linux dig around the system a little bit getting the needed
info to fill in the requested structures.
Secondly the efi_ioctl() call was adapted such that under linux it directly
read or writes out the partition table. Under Solaris this work was
handed off to the kernel via an ioctl. In the efi_write() case we also
ensure we prompt the kernel via BLKRRPART to re-scan the new partition
table. The libefi generated partition tables are correct but older
versions of ~parted-1.8.1 can not read them without a small patch.
The kernel and fdisk are able to read them just fine.
Thirdly efi_alloc_and_init() which is used by zpool to determine if a
device is a 'wholedisk' was updated to be linux aware. This check is
performed by using the partition number for the device, which the
partition number is 0 on linux it is a 'wholedisk'. However, certain
device type such as the loopback and ram disks needed to be excluded
because they do not support partitioning.
Forthly the zpool command was made symlink aware so it can correctly
resolve udev entries such as /dev/disk/by-*/*. This symlinks are
fully expanded ensuring all block devices are recognized. When a
when a 'wholedisk' block device is detected we now properly write
out an efi label and place zfs in the first partition (0th slice).
This partition is created 1MiB in to the disk to ensure it is aligned
nicely with all high end block devices I'm aware of.
This all works for me now but it did take quite a bit of work to get
it all sorted out. It would not surprise me if certain special cases
were missed so we should keep any eye of for any odd behavior.
Brian Behlendorf