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.
Almost exclusively this patch handled the addition of another char
array to the zfs_cmd_t structure. Unfortunately c90 doesn't allow
zero filling the entire struct with the '= { 0 };' shorthand.
Interestingly this has only been a problem on a clean RHEL6
install so I suspect the include was removed from one of the
standard system include headers. We should be including it
explicitly anyway since it's used in both of these .c files.
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.
Based on the block device type we can expect a specific naming
convention. With this in mind update efi_get_info() to be more
aware of the type when parsing out the partition number. In,
addition be aware that all block device types are not partitionable.
Finally, when attempting to lookup a device partition by appending
the partition number to the whole device take in to account the
kernel naming scheme. If the last character of the device name
is a digit the partition will always be 'p#' instead of just '#'.
In check_disk() we should only check the entire device if it
not a whole disk. It is a whole disk with an EFI label on it,
it is possible that libblkid will misidentify the device as a
filesystem. I had a case yesterday where 2 bytes in the EFI
GUID happened we set to the right values such that libblkid
decided there was a minux filesystem there. If it's a whole
device we look for a EFI label.
If we are able to read the backup EFI label from a device but
the primary is corrupt. Then don't bother trying to stat
the partitions in /dev/ the kernel will not create devices
using the backup label when the primary is damaged.
Add code to determine if we have a udev path instead of a
normal device path. In this case use the -part# partition
naming scheme instead of the /dev/disk# scheme. This is
important because we always want to access devices using
the full path provided at configuration time.
Readded support for zpool_relabel_disk() now that we have
the full libefi library in place we do have access to this
functionality.
Lots of additional paranoia to ensure EFI label are written
correctly. These changes include:
1) Removing the O_NDELAY flag when opening a file descriptor
for libefi. This flag should really only be used when you
do not intend to do any file IO. Under Solaris only ioctl()'s
were performed under linux we do perform reads and writes.
2) Use O_DIRECT to ensure any caching is bypassed while
writing or reading the EFI labels. This change forces the
use of sector aligned memory buffers which are allocated
using posix_memalign().
3) Add additional efi_debug error messages to efi_ioctl().
4) While doing a fsync is good to ensure the EFI label is on
disk we can, and should go one step futher by issuing the
BLKFLSBUF ioctl(). This signals the kernel to instruct the
drive to flush it's on-disk cache.
5) Because of some initial strangeness I observed in testing
with some flakey drives be extra paranoid in zpool_label_disk().
After we've written the device without error, flushed the drive
caches, correctly detected the new partitions created by the
kernel. Then additionally read back the EFI label from user
space to make sure it is intact and correct. I don't think we
can ever be to careful here.
NOTE: The was recently some concern expressed that writing EFI
labels from user space on Linux was not the right way to do this.
That instead two kernel ioctl()s should be used to create and
remove partitions. After some investigation it's clear to me
using those ioctl() would be a bad idea. The in fact don't
actually write partition tables to the disk, they only create
the partition devices in the kernel. So what you really want
to do is write the label out from user space, then prompt the
kernel to re-read the partition from disk to create the partitions.
This is in fact exactly what newer version of parted do.
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.
After spending considerable time thinking about this I've come to the
conclusion that on Linux systems we don't need Solaris style devid
support. Instead was can simply use udev if we are careful, there
are even some advantages.
The Solaris style devid's are designed to provide a mechanism by which
a device can be opened reliably regardless of it's location in the system.
This is exactly what udev provides us on Linux, a flexible mechanism for
consistently identifing the same devices regardless of probing order.
We just need to be careful to always open the device by the path provided
at creation time, this path must be stored in ZPOOL_CONFIG_PATH. This
in fact has certain advantages.
For example, if in your system you always want the zpool to be able to
locate the disk regardless of physical location you can create the pool
using /dev/disk/by-id/. This is perhaps what you'ld want on a desktop
system where the exact location is not that important. It's more
critical that all the disks can be found.
However, in an enterprise setup there's a good chace that the physical
location of each drive is important. You have like set things up such
that your raid groups span multiple hosts adapters, such that you can
lose an adapter without downtime. In this case you would want to use
the /dev/disk/by-path/ path to ensure the path information is preserved
and you always open the disks at the right physical locations. This
would ensure your system never gets accidently misconfigured and still
just works because the zpool was still able to locate the disk.
Finally, if you want to get really fancy you can always create your
own udev rules. This way you could implement whatever lookup sceme
you wanted in user space for your drives. This would include nice
cosmetic things like being able to control the device names in tools
like zpool status, since the name as just based of the device names.
I've yet to come up with a good reason to implement devid support on
Linux since we have udev. But I've still just commented it out for now
because somebody might come up with a really good I forgot.
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.
The previous code was not wrong, but this prevents gcc from warning
us about missing cases for these known safe switch statements. The
-Wno-missing-cases can now be removed to detect places where we
accidentally forgot a case.
Brian Behlendorf