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2014-04-25Use error_is_set() only when necessary (again)Markus Armbruster
error_is_set(&var) is the same as var != NULL, but it takes whole-program analysis to figure that out. Unnecessarily hard for optimizers, static checkers, and human readers. Commit 84d18f0 dumbed it down to obvious, but a few more have crept in since, and documentation was overlooked. Dumb these down, too. Signed-off-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-04-25block: Prevent coroutine stack overflow when recursing in ↵Benoît Canet
bdrv_open_backing_file. In 1.7.1 qcow2_create2 reopen the file for flushing without the BDRV_O_NO_BACKING flags. As a consequence the code would recursively open the whole backing chain. These three stack arrays would pile up through the recursion and lead to a coroutine stack overflow. Convert these array to malloced buffers in order to streamline the coroutine footprint. Symptoms where freezes or segfaults on production machines while taking QMP externals snapshots. The overflow disturbed coroutine switching. [Resolved conflicts on qemu.git/master since the patch was against v1.7.1 --Stefan] Signed-off-by: Benoit Canet <benoit.canet@gmail.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-04-22block: Catch duplicate IDs in bdrv_new()Kevin Wolf
Since commit f298d071, block devices added with blockdev-add don't have a QemuOpts around in dinfo->opts. Consequently, we can't rely any more on QemuOpts catching duplicate IDs for block devices. This patch adds a new check for duplicate IDs to bdrv_new(), and moves the existing check that the ID isn't already taken for a node-name there as well. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com>
2014-04-22block: Add errp to bdrv_new()Kevin Wolf
This patch adds an errp parameter to bdrv_new() and updates all its callers. The next patches will make use of this in order to check for duplicate IDs. Most of the callers know that their ID is fine, so they can simply assert that there is no error. Behaviour doesn't change with this patch yet as bdrv_new() doesn't actually assign errors to errp. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com>
2014-04-22block: Remove -errno return value from bdrv_assign_node_nameKevin Wolf
It takes an errp argument. That's enough for error handling. Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-04-22block: Handle error of bdrv_getlength in bdrv_create_dirty_bitmapFam Zheng
bdrv_getlength could fail, check the return value before using it. Return NULL and set errno if it fails. Callers are updated to handle the error case. Signed-off-by: Fam Zheng <famz@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-04-22block: Check bdrv_getlength() return value in bdrv_make_zero()Kevin Wolf
Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-04-22block: Catch integer overflow in bdrv_rw_co()Kevin Wolf
Insanely large requests could cause an integer overflow in bdrv_rw_co() while converting sectors to bytes. This patch catches the problem and returns an error (if we hadn't overflown the integer here, bdrv_check_byte_request() would have rejected the request, so we're not breaking anything that was supposed to work before). We actually do have a test case that triggers behaviour where we accidentally let such a request pass, so that it would return success, but read 0 bytes instead of the requested 4 GB. It fails now like it should. If the vdi block driver wants to be able to deal with huge images, it can't read the whole block bitmap at once into memory like it does today, but needs to use a metadata cache like qcow2 does. Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-04-22block: Limit size to INT_MAX in bdrv_check_byte_request()Kevin Wolf
Commit 8f4754ed intended to protect against integer overflow bugs in block drivers by making sure that a single request that is passed to drivers is no longer than INT_MAX bytes. However, meanwhile there are some callers that don't use that code path any more but call bdrv_check_byte_request() directy, so let's add a check there as well. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-04-22block: Fix nb_sectors check in bdrv_check_byte_request()Kevin Wolf
nb_sectors is signed, check for negative values. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-04-04block: Check bdrv_getlength() return value in bdrv_append_temp_snapshot()Kevin Wolf
Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-04-04block: Fix snapshot=on for protocol parsed from filenameKevin Wolf
Since commit 9fd3171a, BDRV_O_SNAPSHOT uses an option QDict to specify the originally requested image as the backing file of the newly created temporary snapshot. This means that the filename is stored in "file.filename", which is an option that is not parsed for protocol names. Therefore things like -drive file=nbd:localhost:10809 were broken because it looked for a local file with the literal name 'nbd:localhost:10809'. This patch changes the way BDRV_O_SNAPSHOT works once again. We now open the originally requested image as normal, and then do a similar operation as for live snapshots to put the temporary snapshot on top. This way, both driver specific options and parsed filenames work. As a nice side effect, this results in code movement to factor bdrv_append_temp_snapshot() out. This is a good preparation for moving its call to drive_init() and friends eventually. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-04-04block: Don't parse 'filename' optionKevin Wolf
When using the QDict option 'filename', it is supposed to be interpreted literally. The code did correctly avoid guessing the protocol from any string before the first colon, but it still called bdrv_parse_filename() which would, for example, incorrectly remove a 'file:' prefix in the raw-posix driver. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-04-01block: Limit request size (CVE-2014-0143)Kevin Wolf
Limiting the size of a single request to INT_MAX not only fixes a direct integer overflow in bdrv_check_request() (which would only trigger bad behaviour with ridiculously huge images, as in close to 2^64 bytes), but can also prevent overflows in all block drivers. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-03-19block: Add error handling to bdrv_invalidate_cache()Kevin Wolf
If it returns an error, the migrated VM will not be started, but qemu exits with an error message. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Juan Quintela <quintela@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net>
2014-03-14blockdev: Refuse to open encrypted image unless pausedMarkus Armbruster
Opening an encrypted image takes an additional step: setting the key. Between open and the key set, the image must not be used. We have some protection against accidental use in place: you can't unpause a guest while we're missing keys. You can, however, hot-plug block devices lacking keys into a running guest just fine, or insert media lacking keys. In the latter case, notifying the guest of the insert is delayed until the key is set, which may suffice to protect at least some guests in common usage. This patch makes the protection apply in more cases, in a rather heavy-handed way: it doesn't let you open encrypted images unless we're in a paused state. It doesn't extend the protection to users other than the guest (block jobs?). Use of runstate_check() from block.c is disgusting. Best I can do right now. Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-03-13block: Unlink temporary fileMax Reitz
If the image file cannot be opened and was created as a temporary file, it should be deleted; thus, in this case, we should jump to the "unlink_and_fail" label and not just to "fail". Reported-by: Benoît Canet <benoit@irqsave.net> Signed-off-by: Max Reitz <mreitz@redhat.com> Acked-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-03-13block: Rewrite the snapshot authorization mechanism for block filters.Benoît Canet
This patch keep the recursive way of doing things but simplify it by giving two responsabilities to all block filters implementors. They will need to do two things: -Set the is_filter field of their block driver to true. -Implement the bdrv_recurse_is_first_non_filter method of their block driver like it is done on the Quorum block driver. (block/quorum.c) [Paolo Bonzini <pbonzini@redhat.com> pointed out that this patch changes the semantics of blkverify, which now recurses down both bs->file and s->test_file. -- Stefan] Reported-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Benoit Canet <benoit@irqsave.net> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-03-13block: bs->drv may be NULL in bdrv_debug_resume()Max Reitz
Currently, bdrv_debug_resume() requires every bs->drv in the BDS stack to be NULL until a bs->drv with an implementation of bdrv_debug_resume() is found. For a normal function, this would be fine, but this is a function for debugging purposes and should therefore allow intermediate BDS not to have a driver (i.e., be "ejected"). Otherwise, it is hard to debug such situations. Signed-off-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-03-13block: Update image size in bdrv_invalidate_cache()Kevin Wolf
After migration has completed, we call bdrv_invalidate_cache() so that drivers which cache some data drop their stale copy of the data and reread it from the image file to get a new version of data that the source modified while the migration was running. Reloading metadata from the image file is useless, though, if the size of the image file stays stale (this is a value that is cached for all image formats in block.c). Reads from (meta)data after the old EOF return only zeroes, causing image corruption. We need to update bs->total_sectors in all layers that could potentially have changed their size (i.e. backing files are not a concern - if they are changed, we're in bigger trouble) Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-03-06block: Fix error path segfault in bdrv_open()Kevin Wolf
Using an invalid option for a block device that is opened with BDRV_O_PROTOCOL led to drv = NULL, and when trying to include the driver name in the error message, qemu dereferenced it: $ x86_64-softmmu/qemu-system-x86_64 -drive file=/tmp/test.qcow2,file.foo=bar Segmentation fault (core dumped) With this patch applied, the expected error message is printed: $ x86_64-softmmu/qemu-system-x86_64 -drive file=/tmp/test.qcow2,file.foo=bar qemu-system-x86_64: -drive file=/tmp/test.qcow2,file.foo=bar: could not open disk image /tmp/test.qcow2: Block protocol 'file' doesn't support the option 'foo' Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net>
2014-03-06block: Keep "filename" option after parsingMax Reitz
Currently, bdrv_file_open() always removes the "filename" option from the options QDict after bdrv_parse_filename() has been (successfully) called. However, for drivers with bdrv_needs_filename, it makes more sense for bdrv_parse_filename() to overwrite the "filename" option and for bdrv_file_open() to fetch the filename from there. Since there currently are no drivers that implement bdrv_parse_filename() and have bdrv_needs_filename set, this does not change current behavior. Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-03-06block: make bdrv_swap rebuild the bs graph node list field.Benoît Canet
Moving only the node_name one field could lead to some inconsitencies where a node_name was defined on a bs which was not registered in the graph node list. bdrv_swap between a named node bs and a non named node bs would lead to this. bdrv_make_anon would then crash because it would try to remove the bs from the graph node list while it is not in it. This patch remove named node bses from the graph node list before doing the swap then insert them back. Signed-off-by: Benoit Canet <benoit@irqsave.net> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-03-05block: Fix bs->request_alignment assertion for bs->sg=1Kevin Wolf
For sg backends, bs->request_alignment is meaningless and may be 0. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net> Acked-by: Paolo Bonzini <pbonzini@redhat.com>
2014-02-28block: use /var/tmp instead of /tmp for -snapshotAmit Shah
If TMPDIR is not specified, the default was to use /tmp for the working copy of the block devices. Update this to /var/tmp instead, so systems using tmp-on-tmpfs don't end up inadvertently using RAM for the block device. Signed-off-by: Amit Shah <amit.shah@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-02-21block: Remove bdrv_open_image()'s force_raw optionMax Reitz
This option is now unnecessary since specifying BDRV_O_PROTOCOL as flag will do exactly the same. Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-02-21block: Reuse success path from bdrv_open()Max Reitz
The fail and success paths of bdrv_file_open() may be further shortened by reusing code already existent in bdrv_open(). This includes bdrv_file_open() not taking the reference to options which allows the removal of QDECREF(options) in that function. Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-02-21block: Handle bs->options in bdrv_open() onlyMax Reitz
The fail paths of bdrv_file_open() and bdrv_open() naturally exhibit similarities, thus it is possible to reuse the one from bdrv_open() and shorten the one in bdrv_file_open() accordingly. Also, setting bs->options in bdrv_file_open() is not necessary if it is already done in bdrv_open(). Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-02-21block: Remove bdrv_new() from bdrv_file_open()Max Reitz
Change bdrv_file_open() to take a simple pointer to an already existing BDS instead of an indirect one. The BDS will be created in bdrv_open() if necessary. Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-02-21block: Reuse reference handling from bdrv_open()Max Reitz
Remove the reference parameter and the related handling code from bdrv_file_open(), since it exists in bdrv_open() now as well. Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-02-21block: Make bdrv_file_open() staticMax Reitz
Add the bdrv_open() option BDRV_O_PROTOCOL which results in passing the call to bdrv_file_open(). Additionally, make bdrv_file_open() static and therefore bdrv_open() the only way to call it. Consequently, all existing calls to bdrv_file_open() have to be adjusted to use bdrv_open() with the BDRV_O_PROTOCOL flag instead. Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-02-21block: Add reference parameter to bdrv_open()Max Reitz
Allow bdrv_open() to handle references to existing block devices just as bdrv_file_open() is already capable of. Signed-off-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-02-21block: Change BDS parameter of bdrv_open() to **Max Reitz
Make bdrv_open() take a pointer to a BDS pointer, similarly to bdrv_file_open(). If a pointer to a NULL pointer is given, bdrv_open() will create a new BDS with an empty name; if the BDS pointer is not NULL, that existing BDS will be reused (in the same way as bdrv_open() already did). Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2014-02-21block: Fix bdrv_is_first_non_filter()Kevin Wolf
Consider top level BlockDriverStates as well. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net> Tested-by: Benoit Canet <benoit@irqsave.net>
2014-02-20Merge remote-tracking branch 'remotes/qmp-unstable/queue/qmp' into stagingPeter Maydell
* remotes/qmp-unstable/queue/qmp: monitor: Add object_add class argument completion. monitor: Add object_del id argument completion. monitor: Add device_add device argument completion. monitor: Add device_del id argument completion. qmp: expose list of supported character device backends Use error_is_set() only when necessary QMP: allow JSON dict arguments in qmp-shell hmp: migrate command (without -d) now blocks correctly Conflicts: blockdev.c [PMM: resolved trivial conflict in blockdev.c] Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
2014-02-17Use error_is_set() only when necessaryMarkus Armbruster
error_is_set(&var) is the same as var != NULL, but it takes whole-program analysis to figure that out. Unnecessarily hard for optimizers, static checkers, and human readers. Dumb it down to obvious. Gets rid of several dozen Coverity false positives. Note that the obvious form is already used in many places. Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Andreas Färber <afaerber@suse.de> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
2014-02-14block: Open by reference will try device then node_name.Benoît Canet
Since we introduced node_name for named bs of the graph modify the opening by reference to use it as a fallback. This patch also enforce the separation of the device id and graph node namespaces. Signed-off-by: Benoit Canet <benoit@irqsave.net> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-02-14block: Relax bdrv_lookup_bs constraints.Benoît Canet
The following patch will reuse bdrv_lookup_bs in order to open images by references so the rules of usage of bdrv_lookup_bs must be relaxed a bit. Signed-off-by: Benoit Canet <benoit@irqsave.net> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-02-09block: Fix 32 bit truncation in mark_request_serialising()Kevin Wolf
On 32 bit hosts, size_t is too small for align as the bitmask ~(align - 1) will zero out the higher 32 bits of the offset. While at it, change the local overlap_bytes variable to unsigned to match the field in BdrvTrackedRequest. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
2014-02-09block: Don't call ROUND_UP with negative valuesKevin Wolf
The behaviour of the ROUND_UP macro with negative numbers isn't obvious. It happens to do the right thing in this please, but better avoid it. Suggested-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
2014-02-09block: bdrv_aligned_pwritev: Assert overlap rangeKevin Wolf
This adds assertions that the request that we actually end up passing to the block driver (which includes RMW data and has therefore potentially been rounded to alignment boundaries) is fully covered by the overlap_{offset,size} fields of the associated BdrvTrackedRequest. Suggested-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
2014-02-09block: Fix memory leaks in bdrv_co_do_pwritev()Kevin Wolf
The error path for a failure in one of the two bdrv_aligned_preadv() calls leaked head_buf or tail_buf, respectively. This fixes the memory leak. Reported-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
2014-02-09block: Fail gracefully with missing filenameKevin Wolf
This fixes a regression introduced in commit 2a05cbe42 ('block: Allow block devices without files'): $ qemu-system-x86_64 -drive driver=file qemu-system-x86_64: block.c:892: bdrv_open_common: Assertion `!drv->bdrv_needs_filename || filename != ((void *)0)' failed. Now the respective check must be performed not only in bdrv_file_open(), but also in bdrv_open(). Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
2014-01-24block: Switch bdrv_io_limits_intercept() to byte granularityKevin Wolf
Request sizes used to be rounded down to the next sector boundary, allowing to bypass the I/O limit. Now all requests are accounted for with their exact byte size. Reported-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-01-24qemu-iotests: Test pwritev RMW logicKevin Wolf
Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-01-24block: Make bdrv_pwrite() a bdrv_prwv_co() wrapperKevin Wolf
Instead of implementing the alignment adjustment here, use the now existing functionality of bdrv_co_do_pwritev(). Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-01-24block: Make bdrv_pread() a bdrv_prwv_co() wrapperKevin Wolf
Instead of implementing the alignment adjustment here, use the now existing functionality of bdrv_co_do_preadv(). Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-01-24block: Change coroutine wrapper to byte granularityKevin Wolf
Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-01-24block: Assert serialisation assumptions in pwritevKevin Wolf
If a request calls wait_serialising_requests() and actually has to wait in this function (i.e. a coroutine yield), other requests can run and previously read data (like the head or tail buffer) could become outdated. In this case, we would have to restart from the beginning to read in the updated data. However, we're lucky and don't actually need to do that: A request can only wait in the first call of wait_serialising_requests() because we mark it as serialising before that call, so any later requests would wait. So as we don't wait in practice, we don't have to reload the data. This is an important assumption that may not be broken or data corruption will happen. Document it with some assertions. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
2014-01-24block: Align requests in bdrv_co_do_pwritev()Kevin Wolf
This patch changes bdrv_co_do_pwritev() to actually be what its name promises. If requests aren't properly aligned, it performs a RMW. Requests touching the same block are serialised against the RMW request. Further optimisation of this is possible by differentiating types of requests (concurrent reads should actually be okay here). Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Benoit Canet <benoit@irqsave.net>