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Re: [libvirt] [PATCH 2/2] blockjob: wire up online qemu block-commit



On 04.10.2012 16:44, Eric Blake wrote:
> This is the bare minimum to kick off a block commit.  In particular,
> flags support is missing (shallow requires us to crawl the backing
> chain to determine the file name to pass to the qemu monitor command;
> delete requires us to track what needs to be deleted at the time
> the completion event fires), and top must be non-NULL (matching the
> fact that the current qemu code does not support committing the
> active layer, although it is still planned to add that before 1.3).
> Since the active layer won't change, we have it easy and do not have
> to alter the domain XML.  We are also relying on qemu to do some
> error detection on our behalf (such as validating 'top' and 'base'
> as being members of the backing chain).  Additionally, this will
> fail if SELinux is enforcing, because we fail to grant qemu proper
> read/write access to the files it will be modifying.
> 
> * src/qemu/qemu_driver.c (qemuDomainBlockCommit): New function.
> (qemuDriver): Register it.
> ---
>  src/qemu/qemu_driver.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index fddb446..137df7e 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -12529,6 +12529,84 @@ qemuDomainBlockPull(virDomainPtr dom, const char *path, unsigned long bandwidth,
>      return qemuDomainBlockRebase(dom, path, NULL, bandwidth, flags);
>  }
> 
> +
> +static int
> +qemuDomainBlockCommit(virDomainPtr dom, const char *path, const char *base,
> +                      const char *top, unsigned long bandwidth,
> +                      unsigned int flags)
> +{
> +    struct qemud_driver *driver = dom->conn->privateData;
> +    qemuDomainObjPrivatePtr priv;
> +    virDomainObjPtr vm = NULL;
> +    char *device = NULL;
> +    int ret = -1;
> +    virDomainEventPtr event = NULL;

Not used yet. But since this is a stub only it doesn't really matter.

> +    int idx;
> +    virDomainDiskDefPtr disk;
> +
> +    virCheckFlags(0, -1);
> +
> +    if (!(vm = qemuDomObjFromDomain(dom)))
> +        goto cleanup;
> +    priv = vm->privateData;
> +
> +    if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0)
> +        goto cleanup;
> +
> +    if (!virDomainObjIsActive(vm)) {
> +        virReportError(VIR_ERR_OPERATION_INVALID,
> +                       "%s", _("domain is not running"));
> +        goto endjob;
> +    }
> +    if (!qemuCapsGet(priv->caps, QEMU_CAPS_BLOCK_COMMIT) || !top) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> +                       _("online commit of active image not supported with "
> +                         "this QEMU binary"));
> +        goto endjob;
> +    }
> +
> +    device = qemuDiskPathToAlias(vm, path, &idx);
> +    if (!device)
> +        goto endjob;
> +    disk = vm->def->disks[idx];
> +
> +    if (!disk->src) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("disk %s has no source file to be committed"),
> +                       disk->dst);
> +        goto endjob;
> +    }
> +
> +    /* XXX For now, we are relying on qemu to check that 'top' and
> +     * 'base' resolve to members of the backing chain in correct
> +     * order; but if we ever get more paranoid and track the backing
> +     * chain ourself, we should be pre-validating the data rather than
> +     * relying on qemu.  For that matter, we need to be changing the
> +     * SELinux label on both 'base' and the parent of 'top', so that
> +     * qemu can open(O_RDWR) those files for the duration of the
> +     * commit.  */
> +    qemuDomainObjEnterMonitor(driver, vm);
> +    ret = qemuMonitorBlockCommit(priv->mon, device, top, base, bandwidth);
> +    qemuDomainObjExitMonitor(driver, vm);
> +
> +endjob:
> +    if (qemuDomainObjEndJob(driver, vm) == 0) {
> +        vm = NULL;
> +        goto cleanup;
> +    }
> +
> +cleanup:
> +    VIR_FREE(device);
> +    if (vm)
> +        virDomainObjUnlock(vm);
> +    if (event) {
> +        qemuDriverLock(driver);
> +        qemuDomainEventQueue(driver, event);
> +        qemuDriverUnlock(driver);
> +    }
> +    return ret;
> +}
> +
>  static int
>  qemuDomainOpenGraphics(virDomainPtr dom,
>                         unsigned int idx,
> @@ -13871,6 +13949,7 @@ static virDriver qemuDriver = {
>      .domainBlockJobSetSpeed = qemuDomainBlockJobSetSpeed, /* 0.9.4 */
>      .domainBlockPull = qemuDomainBlockPull, /* 0.9.4 */
>      .domainBlockRebase = qemuDomainBlockRebase, /* 0.9.10 */
> +    .domainBlockCommit = qemuDomainBlockCommit, /* 0.10.3 */
>      .isAlive = qemuIsAlive, /* 0.9.8 */
>      .nodeSuspendForDuration = nodeSuspendForDuration, /* 0.9.8 */
>      .domainSetBlockIoTune = qemuDomainSetBlockIoTune, /* 0.9.8 */
> 

Looks good.


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