docs: allow SNAP_INSTANCE_NAME var in content interface paths by Mohit-Chachada · Pull Request #637 · canonical/snap-docs

Mohit-Chachada · 2026-10-15T09:26:32Z

Docs for canonical/snapd#17752

SNAPDENG-37629

Copilot

🟢 Approval recommended

No unresolved review issues were identified.

0 open findings

What changed in this PR

Documents support for $SNAP_INSTANCE_NAME in content interface source paths for parallel-installed snaps.

Changes:

Documents variable usage and snapd version requirements.
Adds producer/consumer configuration and path examples.

File	Summary
`docs/reference/interfaces/content-interface.md`	Documents per-instance content sharing.

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bboozzoo · 2026-10-15T11:14:31Z

 It is recommended to only expose a single `read` path using this configuration.

+(sharing-per-instance-data)=
+### Sharing per-instance data


why not put that under the source section?

moved in 0cbf565

bboozzoo · 2026-10-15T11:25:11Z

+
+_Requires snapd 2.79+._
+
+When a slot's `read` or `write` paths are declared under the `source` section, and a path starts with `$SNAP_DATA` or `$SNAP_COMMON`, it may also reference `$SNAP_INSTANCE_NAME`. This allows a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap to share a separate directory for each of its instances.


The wording makes it sound like a single instance is somehow collecting the data from all other connected slots.

How about:

<right below the using `source` > #### Parallel installed content providers _Requires snapd 2.79+._ Using $`SNAP_INSTANCE_NAME `in the final source path element makes distinguishing data from multiple connected slot providers easier in the plug side snap. Specifically, given the following slot declaration: \``` slots: _slot_name_: interface: content content: assets source: read: - $SNAP_DATA/assets/$SNAP_INSTANCE_NAME \``` and the plug: \``` plugs: _plug_name_: interface: content content: assets target: $SNAP_DATA/assets \``` The plug side connections will be accessible at: \``` $SNAP_DATA/assets/snap-with-slot_foo $SNAP_DATA/assets/snap-with-slot_bar \``` Since `$SNAP_INSTANCE_NAME` is only known at content provider snap installation time, it can only be used when sharing data from writable locations, such as `$SNAP_DATA` or `$SNAP_COMMON`.

Interestingly, I don't get this feeling from the current phrasing.
From my newcomer perspective, I must say I find "makes distinguishing data from multiple connected slot providers easier in the plug side snap" somewhat hard to understand. I wonder whether this is explanation, more than reference. I might be totally wrong, though.

I think examples work wonders.

thanks for the suggestions!
Combined inputs and updated the wording in 0cbf565

raimundo-henriques

Thank you. I left some comments.

raimundo-henriques · 2026-10-15T11:53:19Z


 Read, write and target should start with either ``$SNAP``, ``$SNAP_DATA`` or ``$SNAP_COMMON`` to refer to the designated directory. See {ref}`Environment variables <reference-development-environment-variables>` for details on where these point to on the filesystem.

+Slot paths declared under the `source` section can additionally reference `$SNAP_INSTANCE_NAME`, but only within a path that starts with `$SNAP_DATA` or `$SNAP_COMMON`. This is useful for sharing a separate, per-instance directory with consumers of a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap. See [Sharing per-instance data](#sharing-per-instance-data) below. Requires _snapd_ 2.79+.


Since the rest of the page consistently uses 'source attribute', I think it would be better to keep using that. I also think it is good to avoid 'section', as it is often used to refer to sections in the docs.

Suggested change

Slot paths declared under the `source` section can additionally reference `$SNAP_INSTANCE_NAME`, but only within a path that starts with `$SNAP_DATA` or `$SNAP_COMMON`. This is useful for sharing a separate, per-instance directory with consumers of a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap. See [Sharing per-instance data](#sharing-per-instance-data) below. Requires _snapd_ 2.79+.

Paths declared in a slot's `source` attribute can also reference `$SNAP_INSTANCE_NAME`, but only within a path that starts with `$SNAP_DATA` or `$SNAP_COMMON`. This is useful for sharing a separate, per-instance directory with consumers of a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap. See [Sharing per-instance data](#sharing-per-instance-data) below. Requires _snapd_ 2.79+.

done in 0cbf565

raimundo-henriques · 2026-10-15T11:58:31Z

+
+_Requires snapd 2.79+._
+
+When a slot's `read` or `write` paths are declared under the `source` section, and a path starts with `$SNAP_DATA` or `$SNAP_COMMON`, it may also reference `$SNAP_INSTANCE_NAME`. This allows a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap to share a separate directory for each of its instances.


Same rationale as above and trying to simplify the phrasing a bit.

Suggested change

When a slot's `read` or `write` paths are declared under the `source` section, and a path starts with `$SNAP_DATA` or `$SNAP_COMMON`, it may also reference `$SNAP_INSTANCE_NAME`. This allows a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap to share a separate directory for each of its instances.

When a slot's `source` attribute declares `read` or `write` paths starting with `$SNAP_DATA` or `$SNAP_COMMON`, it may also reference `$SNAP_INSTANCE_NAME`. This allows a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap to share a separate directory for each of its instances.

done in 0cbf565

raimundo-henriques · 2026-10-15T13:01:47Z

+**consumer/snapcraft.yaml**:
+```yaml
+plugs:
+  _plug_name_:


I noticed that we're using _..._ to identify placeholders on this page. As far as I can tell, it's only being done here and in reference/development/environment-variables.md. I know it's not the scope of this PR, but perhaps taking the opportunity to replace the occurrences of _..._ with <...> as a drive-by change, if you wouldn't mind, would be nice.

Suggested change

_plug_name_:

<plug_name>:

done in 0cbf565

raimundo-henriques · 2026-10-15T13:02:59Z

@@ -1 +1 @@
 (interfaces-content-interface)=


Would you mind taking the opportunity to include a metadata description? This is my current proposal.

Suggested change

---

myst:

html_meta:

description: Reference documentation for the content interface, which lets producer snaps share code, data, libraries, and sockets with consumer snaps.

---

(interfaces-content-interface)=

done in 0cbf565

Mohit-Chachada requested a lite review from Copilot October 15, 2026 09:26

Copilot started reviewing on behalf of Mohit-Chachada October 15, 2026 09:27

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Mohit-Chachada requested review from bboozzoo and raimundo-henriques October 15, 2026 09:32

zyga reviewed Oct 15, 2026

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Comment thread docs/reference/interfaces/content-interface.md Outdated

Mohit-Chachada requested a review from zyga October 15, 2026 09:46

bboozzoo reviewed Oct 15, 2026

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raimundo-henriques reviewed Oct 15, 2026

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zyga approved these changes Oct 16, 2026

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Mohit-Chachada added 2 commits October 26, 2026 20:44

docs: allow SNAP_INSTANCE_NAME var in content interface paths

e776c8c

docs: fix review findings

0cbf565

Mohit-Chachada force-pushed the allow-snap-instance-name-var-in-content-interface-paths branch from 25c47c9 to 0cbf565 Compare October 26, 2026 19:45

Mohit-Chachada requested review from bboozzoo and raimundo-henriques October 26, 2026 19:47

Mohit-Chachada closed this Oct 27, 2026

Mohit-Chachada reopened this Oct 27, 2026


		_Requires snapd 2.79+._

		When a slot's `read` or `write` paths are declared under the `source` section, and a path starts with `$SNAP_DATA` or `$SNAP_COMMON`, it may also reference `$SNAP_INSTANCE_NAME`. This allows a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap to share a separate directory for each of its instances.


		Read, write and target should start with either ``$SNAP``, ``$SNAP_DATA`` or ``$SNAP_COMMON`` to refer to the designated directory. See {ref}`Environment variables <reference-development-environment-variables>` for details on where these point to on the filesystem.

		Slot paths declared under the `source` section can additionally reference `$SNAP_INSTANCE_NAME`, but only within a path that starts with `$SNAP_DATA` or `$SNAP_COMMON`. This is useful for sharing a separate, per-instance directory with consumers of a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap. See [Sharing per-instance data](#sharing-per-instance-data) below. Requires _snapd_ 2.79+.

	When a slot's `read` or `write` paths are declared under the `source` section, and a path starts with `$SNAP_DATA` or `$SNAP_COMMON`, it may also reference `$SNAP_INSTANCE_NAME`. This allows a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap to share a separate directory for each of its instances.
	When a slot's `source` attribute declares `read` or `write` paths starting with `$SNAP_DATA` or `$SNAP_COMMON`, it may also reference `$SNAP_INSTANCE_NAME`. This allows a {ref}`parallel-installed <interfaces-parallel-installs>` producer snap to share a separate directory for each of its instances.

+---
+myst:
+  html_meta:
+    description: Reference documentation for the content interface, which lets producer snaps share code, data, libraries, and sockets with consumer snaps.
+---
+(interfaces-content-interface)=

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