loop: Add _from_fd variants for the remaining loop functions by vojtechtrefny · Pull Request #1210 · storaged-project/libblockdev

vojtechtrefny · 2026-09-03T13:03:40Z

Add bd_loop_info_from_fd, bd_loop_teardown_from_fd, bd_loop_set_autoclear_from_fd and bd_loop_set_capacity_from_fd which operate on an already open file descriptor of the loop device instead of opening it by name. This lets consumers open the device early on their side and pass it in, avoiding race conditions.

The existing name-based functions now just open the device and delegate to their _from_fd counterparts (mirroring bd_loop_setup/setup_from_fd) to avoid duplicating the ioctl logic.

Resolves: #1208

Summary by CodeRabbit

New Features
- Added file-descriptor-based operations for retrieving loop-device information, tearing down devices, managing autoclear settings, and updating capacity.
- Existing path-based loop-device operations remain available.
Documentation
- Updated the loop API documentation index with the new operations.
Tests
- Added coverage for loop-device operations using open file descriptors, including offsets, autoclear settings, teardown, and capacity changes.

coderabbitai · 2026-09-03T13:04:01Z

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📝 Walkthrough

Walkthrough

The loop plugin adds four file-descriptor APIs. Path-based functions delegate to these APIs after opening the device. Tests cover teardown, information retrieval, autoclear changes, and capacity refresh.

Changes

Loop file-descriptor API

Layer / File(s)	Summary
File-descriptor API contracts `src/lib/plugin_apis/loop.api`, `src/plugins/loop.h`, `docs/libblockdev-sections.txt`	Defines and documents four APIs for loop-device information, teardown, autoclear, and capacity operations using an open file descriptor.
File-descriptor operation implementation `src/plugins/loop.c`	Adds fd-based ioctl operations and backing-file lookup. Existing path-based functions open the device, delegate to the fd-based functions, and close the descriptor.
File-descriptor operation tests `tests/loop_test.py`	Tests fd-based teardown, information retrieval, autoclear changes, and capacity refresh.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🔵 Low · up to fb1a6

The new loop file-descriptor APIs are mergeable with low risk, but test cleanup may still suppress unexpected teardown failures and leave loop devices allocated.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 73.68% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: adding the remaining `_from_fd` loop function variants.
Linked Issues check	✅ Passed	The pull request satisfies issue `#1208` by adding file-descriptor variants for the remaining loop operations, updating path-based wrappers to delegate to them, and adding coverage for the new API.
Out of Scope Changes check	✅ Passed	The implementation, public API declarations, documentation, and tests are directly related to the linked issue and stated pull request objectives. No unrelated changes are evident.

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Actionable comments posted: 1

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Inline comments:
In `@tests/loop_test.py`:
- Around line 92-93: After a successful BlockDev.loop_teardown_from_fd call in
the test, clear the stale loop-device reference by assigning None to self.loop
before cleanup can run; preserve the existing success assertion.

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docs/libblockdev-sections.txt
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src/plugins/loop.h
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Inline comments:
In `@tests/loop_test.py`:
- Around line 37-38: Update the cleanup around BlockDev.loop_teardown to catch
only the expected already-detached-loop exception instead of using a bare
except, allowing all other teardown failures to propagate before unlinking
self.dev_file.
- Line 97: In the loop cleanup logic, move the self.loop = None assignment until
after self.assertTrue(succ) succeeds, so failed loop_teardown_from_fd calls
retain the loop handle for _clean_up to invoke
BlockDev.loop_teardown(self.loop).

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Add bd_loop_info_from_fd, bd_loop_teardown_from_fd, bd_loop_set_autoclear_from_fd and bd_loop_set_capacity_from_fd which operate on an already open file descriptor of the loop device instead of opening it by name. This lets consumers open the device early on their side and pass it in, avoiding race conditions. The existing name-based functions now just open the device and delegate to their _from_fd counterparts (mirroring bd_loop_setup/setup_from_fd) to avoid duplicating the ioctl logic. Resolves: storaged-project#1208 Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

vojtechtrefny · 2026-09-04T08:18:54Z

/packit test

tbzatek

Nice, thanks!

tbzatek · 2026-09-09T10:05:21Z

+    sys_path = g_strdup_printf ("/sys/dev/block/%u:%u/loop/backing_file",
+                                major (statbuf.st_rdev), minor (statbuf.st_rdev));
+
    if (access (sys_path, R_OK) != 0) {


Do we need this here? The following call to g_file_get_contents() would return an error anyway.

This was interesting investigation -- the check was added intentionally in 4ff2ce4 for the now removed bd_loop_get_backing_file function. It doesn't make sense in the bd_loop_info function, because for non-existing devices it returns error before trying to get the backing file. I removed the check in a separate commit.

This was originally in by the standalone bd_loop_get_backing_file function which didn't want to return error for non-existing loop files. But this function was removed in 3.0 and bd_loop_info always returns error for non-existing loop devices before even trying to get the backing file so the check no longer makes sense, any issues when reading the file will be handled when handling error from the g_file_get_contents call.

coderabbitai Bot reviewed Sep 3, 2026

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Comment thread tests/loop_test.py

vojtechtrefny force-pushed the master_loop-fd branch from d61a829 to 3bf8e12 Compare September 3, 2026 14:54

coderabbitai Bot reviewed Sep 3, 2026

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Comment thread tests/loop_test.py

Comment thread tests/loop_test.py Outdated

vojtechtrefny force-pushed the master_loop-fd branch from 3bf8e12 to 2077c72 Compare September 3, 2026 15:22

tbzatek previously approved these changes Sep 9, 2026

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vojtechtrefny dismissed tbzatek’s stale review via fb1a645 September 10, 2026 12:32

tbzatek approved these changes Sep 10, 2026

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vojtechtrefny merged commit fc8cfc5 into storaged-project:master Sep 10, 2026
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loop: Add _from_fd variants for the remaining loop functions - #1210

loop: Add _from_fd variants for the remaining loop functions#1210
vojtechtrefny merged 2 commits into
storaged-project:masterfrom
vojtechtrefny:master_loop-fd

vojtechtrefny commented Sep 3, 2026 •

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