This change should wrap up the last of the missing block device
support in the vdev_disk layer. With this change I can now
successfully create and use zpools which are layered on top of
md and lvm virtual devices. The following changes include:
1) The big one, properly handle the case when page cannot be added
to a bio due to dynamic limitation of a merge_bdev handler. For
example the md device will limit a bio to the configured stripe
size. Our bio size may also end up being limited by the maximum
request size, and other factors determined during bio construction.
To handle all of the above cases the code has been updated to
handle failures from bio_add_page(). This had been hardcoded to
never fail for the prototype proof of concept implementation. In
the case of a failure the number of bytes which still need to be
added to a bio are returned. New bio's are allocated and attached
to the dio until the entire data buffer is mapped to bios. It is
then submitted as before to the request queue, and once all the bio's
attached to a dio have finished the completion callback is run.
2) The devid comments have been removed because it is not clear to
me that we will not need devid support. They have been replaced
with a comment explaining that udev can and should be used.
Remove the hard coded 512 byte SECTOR_SIZE and replace it with
bdev_hardsect_size() to get the correct hardware sector size.
Usage of get_capacity() was incorrect. We the block_device
references a partition we need to return bdev->part->nr_sects.
If get_capacity() is used the entire device size will be returned
ignoring partition information. This is however the correct thing
to do when the block device in question has not partition table.
Exposed by the fc11 debug kernel we need to hold a reference over all
calls to submit_bio(). Otherwise it is possible all the completion
callbacks run before we exit __vdev_disk_physio(), and we end up with
a GPF. This was quickly exposed when slab poisoning was enabled. I
have added helper functions to cleanly track the reference counts. In
addition dr->dr_ref was converted from an integer to an atomic type
which removes the need for the spinlock. As a nice side effect of
these changes the code is now slightly cleaner and clearer.
There is concern that READA may do more than simply reorder the queue.
There may be an increased chance that a requested marked READA will
fail because the elevator considers it optional. For this reason, all
read requests, even speculative ones, have been converted back to READ.
Tested under CHAOS4.2, RHEL5, SLES11, and FC11 (all x86_64)
Features:
Honor spa_mode() when opening the block device. Previously this
was ignored and devices were always opened read/write.
Integrated DKIOCFLUSHWRITECACHE zio operation with linux WRITE_BARRIER
for kernels post 2.6.24 where empty bio requests are supported. For
earlier kernels ENOTSUP is returned and no barriers are performed. If
RHEL5 based kernels are intended to be supported long term we may need
make use of the old akward API.
With the addition of WRITE_BARRIER support all writes which were
WRITE_SYNC can now be safely made WRITE bios. They will now take
advantage of aggregation in the elevator and improved write performance
is likely.
Notice the ZIO_FLAG_SPECULATIVE flag and pass along the hint to the
elevator by using READA instead of READ. This provides the elevator
the ability to prioritize the real READs ahead of the speculative IO
if needed.
Implement an initial version of vdev_disk_io_done() which in the case
of an EIO error triggers a media change check. If it determines a
media change has occured we fail the device and remove it from the
config. This logic I'm sure can be improved further but for now it
is an improvement over the VERIFY() that no error will ever happen.
APIs:
2.6.22 API change
Unused destroy_dirty_buffers arg removed from prototype.
2.6.24 API change
Empty write barriers are now supported and we should use them.
2.6.24 API change
Size argument dropped from bio_endio and bi_end_io, because the
bi_end_io is only called once now when the request is complete.
There is no longer any need for a size argument. This also means
that partial IO's are no longer possibe and the end_io callback
should not check bi->bi_size. Finally, the return type was updated
to void.
2.6.28 API change
open/close_bdev_excl() renamed to open/close_bdev_exclusive().
2.6.29 API change
BIO_RW_SYNC renamed to BIO_RW_SYNCIO.
Use the legacy BIO_RW_FAILFAST flag if it exists. If it is missing it
means we are running against a kernel with the newer API. We should
be able to enable some fairly smart behavior one we intergrate with the
new API, but until I get around to writing that code just remove the
flag entirely. It's not critical for correctness.
Kernel commit 6712ecf8f648118c3363c142196418f89a510b90 which removes the
size argument from bio_endio and bi_end_io, also removes the need to
handle partial IOs in the handler.
Brian Behlendorf