Re: [EXTERNAL] PyDM Write Widgets Do Not Honor PVA ACF Permission Rules

["Kasemir, Kay via Tech-talk" <tech-talk at aps.anl.gov>]

At this time, the PVA protocol doesn’t support access information.

In other words, the protocol doesn’t tell you ahead of time if you have write access.

If you can’t write, you only notice that once you try to write and then you get an error reply.

See https://github.com/epics-docs/epics-docs/pull/140 for the ongoing effort to add permission into to the protocol.

-Kay

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of lvhh--- via Tech-talk <tech-talk at aps.anl.gov>
Date: Wednesday, May 13, 2026 at 10:19 PM
To: tech-talk <tech-talk at aps.anl.gov>
Subject: [EXTERNAL] PyDM Write Widgets Do Not Honor PVA ACF Permission Rules

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Hi all,

We develop OPIs using PyDM. All functions work properly when using the CA protocol. However, we have encountered a permission‑enforcement problem under the PVA protocol.

Specifically, PyDM write‑enabled widgets fail to comply with access permission rules defined in the PVA ACF security file. Even though write access is explicitly denied in the ACF configuration, value writing is still allowed on the PyDM GUI interface.

Thanks for your reply.

Huihui

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lvhh at sari.ac.cn