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Re: [Qemu-devel] [PATCH v3 09/11] authz: add QAuthZListFile object type
From: |
Daniel P . Berrangé |
Subject: |
Re: [Qemu-devel] [PATCH v3 09/11] authz: add QAuthZListFile object type for a file access control list |
Date: |
Wed, 20 Jun 2018 12:11:07 +0100 |
User-agent: |
Mutt/1.9.5 (2018-04-13) |
On Wed, Jun 20, 2018 at 11:58:01AM +0100, Dr. David Alan Gilbert wrote:
> * Daniel P. Berrangé (address@hidden) wrote:
> > Add a QAuthZListFile object type that implements the QAuthZ interface. This
> > built-in implementation is a proxy around the QAtuhZList object type,
> > initializing it from an external file, and optionally, automatically
> > reloading it whenever it changes.
> >
> > To create an instance of this object via the QMP monitor, the syntax
> > used would be:
> >
> > {
> > "execute": "object-add",
> > "arguments": {
> > "qom-type": "authz-list-file",
> > "id": "authz0",
> > "parameters": {
> > "filename": "/etc/qemu/vnc.acl",
> > "refresh": "yes"
> > }
> > }
> > }
> >
> > If "refresh" is "yes", inotify is used to monitor the file,
> > automatically reloading changes. If an error occurs during reloading,
> > all authorizations will fail until the file is next successfully
> > loaded.
>
> I'm curious about the 'refresh' stuff:
> a) If refresh=no is there a way to explicitly ask for a refresh
> when some tool knows it's finished with fiddling with the file.
If refresh=no, then you can still use object_del + object_add to
recreate the ACL object which will cause new content to be picked
up.
> b) am I right in thinking you're actually monitoring the directory
> for changes and retriggering on directory changes? So it'll
> trigger on the normal trick of renaming the modified file over the
> original?
I originally made the mistake of trying to monitor the file
and discovered the awfulness of inotify :-(
So, yeah, now we monitor the directory so we can trigger
reloads even when the file is editted by doing a tmpfile+rename
dance.
The inotify support in the early patch in this series is intelligent
so that if multiple objects all monitor the same directory we only
use a single inotify watch.
> c) I'm a little concerned about making it automatic; if all the qemus
> on a system all wake up and reparse the file at the same time.
I don't think its a big deal in this case because the files in
question are very small. Once one QEMU reads it, the kernel will
have content in I/O cache, and the CPU overhead of parsing the JSON
will be lost in the noise given likely file sizes IMHO.
Regards,
Daniel
--
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- [Qemu-devel] [PATCH v3 00/11] Add a standard authorization framework, Daniel P . Berrangé, 2018/06/20
- [Qemu-devel] [PATCH v3 02/11] qom: don't require user creatable objects to be registered, Daniel P . Berrangé, 2018/06/20
- [Qemu-devel] [PATCH v3 03/11] hw/usb: don't set IN_ISDIR for inotify watch in MTP driver, Daniel P . Berrangé, 2018/06/20
- [Qemu-devel] [PATCH v3 01/11] util: add helper APIs for dealing with inotify in portable manner, Daniel P . Berrangé, 2018/06/20
- [Qemu-devel] [PATCH v3 04/11] hw/usb: fix const-ness for string params in MTP driver, Daniel P . Berrangé, 2018/06/20
- [Qemu-devel] [PATCH v3 05/11] hw/usb: switch MTP to use new inotify APIs, Daniel P . Berrangé, 2018/06/20
- [Qemu-devel] [PATCH v3 07/11] authz: add QAuthZSimple object type for easy whitelist auth checks, Daniel P . Berrangé, 2018/06/20
- [Qemu-devel] [PATCH v3 06/11] authz: add QAuthZ object as an authorization base class, Daniel P . Berrangé, 2018/06/20
- [Qemu-devel] [PATCH v3 09/11] authz: add QAuthZListFile object type for a file access control list, Daniel P . Berrangé, 2018/06/20
[Qemu-devel] [PATCH v3 08/11] authz: add QAuthZList object type for an access control list, Daniel P . Berrangé, 2018/06/20
[Qemu-devel] [PATCH v3 10/11] authz: add QAuthZPAM object type for authorizing using PAM, Daniel P . Berrangé, 2018/06/20
[Qemu-devel] [PATCH v3 11/11] authz: delete existing ACL implementation, Daniel P . Berrangé, 2018/06/20