[pve-devel] qemu2.7: cpu hotplug && hot-unplug v1

[Alexandre DERUMIER]

>>No idea (and no docs/examples available?) 

I think using aiocontext is enough.
(But I think that iothread still need to be enable on block device to use a different aiocontext than the main qemu context)

look at the simple qmp_block_resize


void qmp_block_resize(bool has_device, const char *device,
                      bool has_node_name, const char *node_name,
                      int64_t size, Error **errp)
{
    Error *local_err = NULL;
    BlockDriverState *bs;
    AioContext *aio_context;
    int ret;

    bs = bdrv_lookup_bs(has_device ? device : NULL,
                        has_node_name ? node_name : NULL,
                        &local_err);
    if (local_err) {
        error_propagate(errp, local_err);
        return;
    }

    aio_context = bdrv_get_aio_context(bs);
    aio_context_acquire(aio_context);

    if (!bdrv_is_first_non_filter(bs)) {
        error_setg(errp, QERR_FEATURE_DISABLED, "resize");
        goto out;
    }


    /* complete all in-flight operations before resizing the device */
    bdrv_drain_all();

    if (size < 0) {
        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "size", "a >0 size");
        goto out;
    }

    if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_RESIZE, NULL)) {
        error_setg(errp, QERR_DEVICE_IN_USE, device);
        goto out;
    }

    /* complete all in-flight operations before resizing the device */
    bdrv_drain_all();

    ret = bdrv_truncate(bs, size);
    switch (ret) {
    case 0:
        break;
    case -ENOMEDIUM:
        error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
        break;
    case -ENOTSUP:
        error_setg(errp, QERR_UNSUPPORTED);
        break;
    case -EACCES:
        error_setg(errp, "Device '%s' is read only", device);
        break;
    case -EBUSY:
        error_setg(errp, QERR_DEVICE_IN_USE, device);
        break;
    default:
        error_setg_errno(errp, -ret, "Could not resize");
        break;
    }

out:
    aio_context_release(aio_context);
}


----- Mail original -----
De: "dietmar" <dietmar at proxmox.com>
À: "aderumier" <aderumier at odiso.com>
Cc: "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Lundi 12 Septembre 2016 17:36:45
Objet: Re: [pve-devel] qemu2.7: cpu hotplug && hot-unplug v1

> >>I also wonder if it would make sense to run the backup code 
> >>inside its own thread? I guess this would make the code simpler. 
> 
> Yes. It can have big advantage. 
> 
> If it share the main qemu thread, this can make slowdown or qemu hang is 
> backup process is hanging. 
> 
> Not sure how it's implemented in qemu drive_backup ? 

No idea (and no docs/examples available?)