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staging
# gpg: Signature made Mon 22 Sep 2014 12:41:59 BST using RSA key ID 81AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg: aka "Stefan Hajnoczi <stefanha@gmail.com>"
* remotes/stefanha/tags/block-pull-request: (59 commits)
block: Always compile virtio-blk dataplane
vring: Better error handling if num is too large
virtio: Import virtio_vring.h
async: aio_context_new(): Handle event_notifier_init failure
block: vhdx - fix reading beyond pointer during image creation
block: delete cow block driver
block/archipelago: Fix typo in qemu_archipelago_truncate()
ahci: Add test_identify case to ahci-test.
ahci: Add test_hba_enable to ahci-test.
ahci: Add test_hba_spec to ahci-test.
ahci: properly shadow the TFD register
ahci: add test_pci_enable to ahci-test.
ahci: Add test_pci_spec to ahci-test.
ahci: MSI capability should be at 0x80, not 0x50.
ahci: Adding basic functionality qtest.
layout: Add generators for refcount table and blocks
fuzz: Add fuzzing functions for entries of refcount table and blocks
docs: List all image elements currently supported by the fuzzer
qapi/block-core: Add "new" qcow2 options
qcow2: Add overlap-check.template option
...
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
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In vhdx_create_metadata(), we allocate 40 bytes to entry_buffer for
the various metadata table entries. However, we write out 64kB from
that buffer into the new file. Only write out the correct 40 bytes.
Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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This patch removes support for the cow file format.
Normally we do not break backwards compatibility but in this case there
is no impact and it is the most logical option. Extraordinary claims
require extraordinary evidence so I will show why removing the cow block
driver is the right thing to do.
The cow file format is the disk image format for Usermode Linux, a way
of running a Linux system in userspace. The performance of UML was
never great and it was hacky, but it enjoyed some popularity before
hardware virtualization support became mainstream.
QEMU's block/cow.c is supposed to read this image file format.
Unfortunately the file format was underspecified:
1. Earlier Linux versions used the MAXPATHLEN constant for the backing
filename field. The value of MAXPATHLEN can change, so Linux
switched to a 4096 literal but QEMU has a 1024 literal.
2. Padding was not used on the header struct (both in the Linux kernel
and in QEMU) so the struct layout varied across architectures. In
particular, i386 and x86_64 were different due to int64_t alignment
differences. Linux now uses __attribute__((packed)), QEMU does not.
Therefore:
1. QEMU cow images do not conform to the Linux cow image file format.
2. cow images cannot be shared between different host architectures.
This means QEMU cow images are useless and QEMU has not had bug reports
from users actually hitting these issues.
Let's get rid of this thing, it serves no purpose and no one will be
affected.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 1410877464-20481-1-git-send-email-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Fix a typo introduced by 94c80a438c85f2c19698547fbb115ea46d80c5f1
Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Being able to set the overlap-check option to a string and then refine
it via the overlap-check.* options is a nice idea for the command line
but does not work so well for non-flattened dicts. In that case, one can
only specify either but not both, so add a field to overlap-check.*
which does the same as directly specifying overlap-check but can be used
in conjunction with the other fields in non-flattened dicts.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1408557576-14574-4-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Currently, the QemuOpts object opts is leaked if anything fails from its
creation up to and including the image repair block. Fix this by freeing
that object in the fail path.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Message-id: 1408557576-14574-2-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Offsets taken from the L1, L2 and refcount tables are generally assumed
to be correctly aligned. However, this cannot be guaranteed if the image
has been written to by something different than qemu, thus check all
offsets taken from these tables for correct cluster alignment.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1409926039-29044-5-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Use the new function in case of a failed overlap check.
This changes output in case of corruption, so adapt iotest 060's
reference output accordingly.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Message-id: 1409926039-29044-4-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Add a helper function for easily marking an image corrupt (on fatal
corruptions) while outputting an informative message to stderr and via
QAPI.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Message-id: 1409926039-29044-3-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Not every BLOCK_IMAGE_CORRUPTED event must be fatal; for example, when
reading from an image, they should generally not be. Nonetheless, even
an image only read from may of course be corrupted and this can be
detected during normal operation. In this case, a non-fatal event should
be emitted, but the image should not be marked corrupt (in accordance to
"fatal" set to false).
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1409926039-29044-2-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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This is an analogue to Linux null_blk. It can be used for testing or
benchmarking block device emulation and general block layer
functionalities such as coroutines and throttling, where disk IO is not
necessary or wanted.
Use null-aio:// for AIO version, and null-co:// for coroutine version.
[Resolved conflict with Fam's async bdrv_aio_cancel() series:
1. Drop .bdrv_aio_cancel() since it is now done by block.c
2. Rename qemu_aio_release() to qemu_aio_unref()
--Stefan]
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1410415798-20673-2-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Suggested-by: Benoît Canet <benoit.canet@irqsave.net>
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Also drop the now unused SheepdogAIOCB.finished field. Note that this
aio is internal to sheepdog driver and has NULL cb and opaque, and
should be unused at all.
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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And also drop the now unused "cancelled" field.
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Before, we cancel all the child requests with bdrv_aio_cancel, then free
the acb..
Now we just kick off asynchronous cancellation of child requests and
return, we know quorum_aio_cb will be called later, so in the end
quorum_aio_finalize will take care of calling the caller's cb.
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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For a fifo read pattern, we only have one running aio (possible other cases that
has less number than num_children in the future), so we need to check if
.acb is NULL against bdrv_aio_cancel() to avoid segfault.
Cc: Eric Blake <eblake@redhat.com>
Cc: Benoit Canet <benoit@irqsave.net>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Also drop the now unused ->finished field.
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Also the finished pointer is not used any more.
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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The cancelled flag is no longer useful. Later the request will complete
as before, and cb will be called.
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Also drop the unused field "canceled".
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Just call io_cancel (2), if it fails, it means the request is not
canceled, so the event loop will eventually call
qemu_laio_process_completion.
In qemu_laio_process_completion, change to call the cb unconditionally.
It is required by bdrv_aio_cancel_async.
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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The parent_vhdx_guid variable is defined but never used, which provokes
complaints from newer versions of clang. Since the variable definition
is here acting as documentation of the image format, mark it with the
'unused' attribute to keep the compiler happy rather than simply
deleting it.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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When trying to create a fixed vhd image qemu-img will return the
following error:
qemu-img: test.vhdx: Could not create image: Cannot allocate memory
This happens because of a incorrect check in vhdx.c. Specifficaly,
in vhdx_create_bat(), after allocating memory for the BAT entry,
there is a check to determine if the allocation was unsuccsessful.
The error comes from the fact that it checks if s->bat isn't NULL,
which is true in case of succsessful allocation, and exits with
error ENOMEM.
Signed-off-by: Adelina Tuvenie <atuvenie@cloudbasesolutions.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
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preallocation=falloc allocates disk space by posix_fallocate(),
preallocation=full allocates disk space by writing zeros to disk.
Both modes imply preallocation=metadata.
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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This patch adds a new option preallocation for raw format, and implements
falloc and full preallocation.
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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This patch prepares for the subsequent patches.
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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and avoid converting it back later.
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Currently the file size requested by user is rounded down to nearest
sector, causing the actual file size could be a bit less than the size
user requested. Since some formats (like qcow2) record virtual disk
size in bytes, this can make the last few bytes cannot be accessed.
This patch fixes it by rounding up file size to nearest sector so that
the actual file size is no less than the requested file size.
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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This is the next step for decoupling block accounting functions from
BlockDriverState.
In a future commit the BlockAcctStats structure will be moved from
BlockDriverState to the device models structures.
Note that bdrv_get_stats was introduced so device models can retrieve the
BlockAcctStats structure of a BlockDriverState without being aware of it's
layout.
This function should go away when BlockAcctStats will be embedded in the device
models structures.
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Keith Busch <keith.busch@intel.com>
CC: Anthony Liguori <aliguori@amazon.com>
CC: "Michael S. Tsirkin" <mst@redhat.com>
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Eric Blake <eblake@redhat.com>
CC: Peter Maydell <peter.maydell@linaro.org>
CC: Michael Tokarev <mjt@tls.msk.ru>
CC: John Snow <jsnow@redhat.com>
CC: Markus Armbruster <armbru@redhat.com>
CC: Alexander Graf <agraf@suse.de>
CC: Max Reitz <mreitz@redhat.com>
Signed-off-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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The middle term goal is to move the BlockAcctStats structure in the device models.
(Capturing I/O accounting statistics in the device models is good for billing)
This patch make a small step in this direction by removing a reference to BDRV.
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Keith Busch <keith.busch@intel.com>
CC: Anthony Liguori <aliguori@amazon.com>
CC: "Michael S. Tsirkin" <mst@redhat.com>
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: John Snow <jsnow@redhat.com>
CC: Richard Henderson <rth@twiddle.net>
CC: Markus Armbruster <armbru@redhat.com>
CC: Alexander Graf <agraf@suse.de>i
Signed-off-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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The plan is to add new accounting metrics (latency, invalid requests, failed
requests, queue depth) and block.c is overpopulated so it will be better to work
in a separate module.
Moreover the long term plan is to have statistics in each of the BDS of the graph
for metrology purpose; this means that the device model statistics must move from
the topmost BDS to the device model.
So we need to decouple the statistic code from BlockDriverState.
This is another argument for the extraction of the code in a separate module.
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
CC: Eric Blake <eblake@redhat.com>
CC: Benoit Canet <benoit@irqsave.net>
CC: Fam Zheng <famz@redhat.com>
CC: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
CC: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Extract the block accounting statistics into a structure so the block device
models can hold them in the future.
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
CC: Eric Blake <eblake@redhat.com>
Signed-off-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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cpu_to_be32() is wrong since vhd_type is an enum constant
(just a regular CPU-endian integer).
Signed-off-by: Xiaodong Gong <gordongong0350@gmail.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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vmdk_open_sparse() does not take ownership of buf so the caller always
needs to free it.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
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Replace __sync builtins with ones provided by QEMU
for atomic operations.
Special thanks goes to Paolo Bonzini for his refactoring
suggestion in order to use the already existing atomic builtins
interface.
Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
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Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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In commit 63f0f45f2e89b60ff8245fec81328ddfde42a303 the following
mechanical change was made:
if (!state) {
- qemu_aio_wait();
+ aio_poll(state->s->aio_context, true);
}
The new code now checks if state is NULL and then dereferences it
('state->s') which is obviously incorrect.
This commit replaces state->s->aio_context with
bdrv_get_aio_context(bs), fixing this problem. The two other hunks
are concerned with getting the BlockDriverState pointer bs to where it
is needed.
The original bug causes a segfault when using libguestfs to access a
VMware vCenter Server and doing any kind of complex read-heavy
operations. With this commit the segfault goes away.
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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In order to access VMware ESX efficiently, we need to send a session
cookie. This patch is very simple and just allows you to send that
session cookie. It punts on the question of how you get the session
cookie in the first place, but in practice you can just run a `curl'
command against the server and extract the cookie that way.
To use it, add file.cookie to the curl URL. For example:
$ qemu-img info 'json: {
"file.driver":"https",
"file.url":"https://vcenter/folder/Windows%202003/Windows%202003-flat.vmdk?dcPath=Datacenter&dsName=datastore1",
"file.sslverify":"off",
"file.cookie":"vmware_soap_session=\"52a01262-bf93-ccce-d379-8dabb3e55560\""}'
image: [...]
file format: raw
virtual size: 8.0G (8589934592 bytes)
disk size: unavailable
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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If two Linux AIO request completions are fetched in the same
io_getevents() call, QEMU will deadlock if request A's callback waits
for request B to complete using an aio_poll() loop. This was reported
to happen with the mirror blockjob.
This patch moves completion processing into a BH and makes it resumable.
Nested event loops can resume completion processing so that request B
will complete and the deadlock will not occur.
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ming Lei <ming.lei@canonical.com>
Cc: Marcin Gibuła <m.gibula@beyond.pl>
Reported-by: Marcin Gibuła <m.gibula@beyond.pl>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Marcin Gibuła <m.gibula@beyond.pl>
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We should reinit local_err as NULL inside the while loop or g_free() will report
corrupption and abort the QEMU when sheepdog driver tries reconnecting.
This was broken in commit 356b4ca.
qemu-system-x86_64: failed to get the header, Resource temporarily unavailable
qemu-system-x86_64: Failed to connect to socket: Connection refused
qemu-system-x86_64: (null)
[xcb] Unknown sequence number while awaiting reply
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
qemu-system-x86_64: ../../src/xcb_io.c:298: poll_for_response: Assertion `!xcb_xlib_threads_sequence_lost' failed.
Aborted (core dumped)
Cc: qemu-devel@nongnu.org
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Uses the same select/WSAEventSelect scheme as main-loop.c.
WSAEventSelect() is edge-triggered, so it cannot be used
directly, but it is still used as a way to exit from a
blocking g_poll().
Before g_poll() is called, we poll sockets with a non-blocking
select() to achieve the level-triggered semantics we require:
if a socket is ready, the g_poll() is made non-blocking too.
Based on a patch from Or Goshen.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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This patch adds single read pattern to quorum driver and quorum vote is default
pattern.
For now we do a quorum vote on all the reads, it is designed for unreliable
underlying storage such as non-redundant NFS to make sure data integrity at the
cost of the read performance.
For some use cases as following:
VM
--------------
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v v
A B
Both A and B has hardware raid storage to justify the data integrity on its own.
So it would help performance if we do a single read instead of on all the nodes.
Further, if we run VM on either of the storage node, we can make a local read
request for better performance.
This patch generalize the above 2 nodes case in the N nodes. That is,
vm -> write to all the N nodes, read just one of them. If single read fails, we
try to read next node in FIFO order specified by the startup command.
The 2 nodes case is very similar to DRBD[1] though lack of auto-sync
functionality in the single device/node failure for now. But compared with DRBD
we still have some advantages over it:
- Suppose we have 20 VMs running on one(assume A) of 2 nodes' DRBD backed
storage. And if A crashes, we need to restart all the VMs on node B. But for
practice case, we can't because B might not have enough resources to setup 20 VMs
at once. So if we run our 20 VMs with quorum driver, and scatter the replicated
images over the data center, we can very likely restart 20 VMs without any
resource problem.
After all, I think we can build a more powerful replicated image functionality
on quorum and block jobs(block mirror) to meet various High Availibility needs.
E.g, Enable single read pattern on 2 children,
-drive driver=quorum,children.0.file.filename=0.qcow2,\
children.1.file.filename=1.qcow2,read-pattern=fifo,vote-threshold=1
[1] http://en.wikipedia.org/wiki/Distributed_Replicated_Block_Device
[Dropped \n from an error_setg() error message
--Stefan]
Cc: Benoit Canet <benoit@irqsave.net>
Cc: Eric Blake <eblake@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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