Zero writes are a dedicated interface for writing regions of zeroes into
the image file. If clusters are not yet allocated it is possible to use
an efficient metadata representation which keeps the image file compact
and does not store individual zero bytes.
Implementing this for the QED image format is fairly straightforward.
The only issue is that when a zero write touches an existing cluster we
have to allocate a bounce buffer and perform a regular write.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Per-request attributes like read/write are currently implemented as bool
fields in the QEDAIOCB struct. This becomes unwiedly as the number of
attributes grows. For example, the qed_aio_setup() function would have
to take multiple bool arguments and at call sites it would be hard to
distinguish the meaning of each bool.
Instead use a flags field with bitmask constants. This will be used
when zero write support is added.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Now when you try to migrate with qed, you get:
(qemu) migrate tcp:localhost:1025
Block format 'qed' used by device 'ide0-hd0' does not support feature 'live migration'
(qemu)
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
One strategy to limit the startup delay of consistency check when
opening image files is to ensure that the file is marked dirty for as
little time as possible.
QED currently marks the image dirty when the first allocating write
request is issued and clears the dirty bit again when the image is
cleanly closed. In practice that means the image is marked dirty for
most of a guest's lifetime and prone to being in a dirty state upon
crash or power failure.
It is safe to clear the dirty bit after all allocating write requests
have completed and a flush has been performed. This patch adds a timer
after the last allocating write request completes. When the timer fires
it will flush and then clear the dirty bit. The timer is set to 5
seconds and is cancelled upon arrival of a new allocating write request.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
The qed_bytes_to_clusters() function is normally used with size_t
lengths. Consistency check used it with file size length and therefore
failed on 32-bit hosts when the image file is 4 GB or more.
Make qed_bytes_to_clusters() explicitly 64-bit and update consistency
check to keep 64-bit cluster counts.
Reported-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Zero clusters are similar to unallocated clusters except instead of reading
their value from a backing file when one is available, the cluster is always
read as zero.
This implements read support only. At this stage, QED will never write a
zero cluster.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This patch adds support for the qemu-img check command. It also
introduces a dirty bit in the qed header to mark modified images as
needing a check. This bit is cleared when the image file is closed
cleanly.
If an image file is opened and it has the dirty bit set, a consistency
check will run and try to fix corrupted table offsets. These
corruptions may occur if there is power loss while an allocating write
is performed. Once the image is fixed it opens as normal again.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This patch implements the read/write state machine. Operations are
fully asynchronous and multiple operations may be active at any time.
Allocating writes lock tables to ensure metadata updates do not
interfere with each other. If two allocating writes need to update the
same L2 table they will run sequentially. If two allocating writes need
to update different L2 tables they will run in parallel.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This patch adds code to look up data cluster offsets in the image via
the L1/L2 tables. The L2 tables are writethrough cached in memory for
performance (each read/write requires a lookup so it is essential to
cache the tables).
With cluster lookup code in place it is possible to implement
bdrv_is_allocated() to query the number of contiguous
allocated/unallocated clusters.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This patch introduces the qed on-disk layout and implements image
creation. Later patches add read/write and other functionality.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Stefan Hajnoczi