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Re: [Qemu-devel] [PATCH for-2.8] monitor: fix object_del for command-lin
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH for-2.8] monitor: fix object_del for command-line-created objects |
Date: |
Wed, 30 Nov 2016 20:33:56 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 |
On 11/30/2016 05:06 PM, Michael Roth wrote:
> Currently objects specified on the command-line are only partially
> cleaned up when 'object_del' is issued in either HMP or QMP: the
> object itself is fully finalized, but the QemuOpts are not removed.
> This results in the following behavior:
>
> x86_64-softmmu/qemu-system-x86_64 -monitor stdio \
> -object memory-backend-ram,id=ram1,size=256M
>
> QEMU 2.7.91 monitor - type 'help' for more information
> (qemu) object_del ram1
> (qemu) object_del ram1
> object 'ram1' not found
> (qemu) object_add memory-backend-ram,id=ram1,size=256M
> Duplicate ID 'ram1' for object
> Try "help object_add" for more information
>
> which can be an issue for use-cases like memory hotplug.
Nice analysis.
>
> This happens on the HMP side because hmp_object_add() attempts to
> create a temporary QemuOpts entry with ID 'ram1', which ends up
> conflicting with the command-line-created entry, since it was never
> cleaned up during the previous hmp_object_del() call.
>
> We address this by adding checks in {qmp,hmp}_object_del to determine
> whether an option group entry matching the object's ID is present,
> and removing it if it is.
>
> Note that qmp_object_add() never attempts to create a temporary
> QemuOpts entry, so it does not encounter the duplicate ID error,
> which is why this isn't generally visible in libvirt.
Phew. Yeah, libvirt avoiding HMP where possible saves a lot of hassles.
> +++ b/hmp.c
> @@ -2072,6 +2072,16 @@ void hmp_object_del(Monitor *mon, const QDict *qdict)
>
> user_creatable_del(id, &err);
> hmp_handle_error(mon, &err);
> +
> + /* if object was defined on the command-line, remove its corresponding
> + * option group entry
> + */
> + if (err == NULL) {
> + QemuOptsList *opt_group = qemu_find_opts_err("object", &err);
> + if (opt_group) {
> + qemu_opts_del(qemu_opts_find(opt_group, id));
> + }
> + }
This one looks okay.
> }
>
> void hmp_info_memdev(Monitor *mon, const QDict *qdict)
> diff --git a/qmp.c b/qmp.c
> index 0028f0b..87c545d 100644
> --- a/qmp.c
> +++ b/qmp.c
> @@ -686,6 +686,16 @@ void qmp_object_add(const char *type, const char *id,
> void qmp_object_del(const char *id, Error **errp)
> {
> user_creatable_del(id, errp);
> +
> + /* if object was defined on the command-line, remove its corresponding
> + * option group entry
> + */
> + if (!(errp && *errp)) {
But this is wrong. Please spin a v2 that uses a local Error object, then
use error_propagate(err, errp). Making anything conditional on whether
an error occurred requires a local object, since the caller can pass in
NULL, but you want your cleanup to happen even when the caller doesn't
care about errors.
> + QemuOptsList *opt_group = qemu_find_opts_err("object", errp);
> + if (opt_group) {
> + qemu_opts_del(qemu_opts_find(opt_group, id));
> + }
> + }
> }
>
> MemoryDeviceInfoList *qmp_query_memory_devices(Error **errp)
>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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