fix: false hdd detection on virtual devices by KSXGitHub · Pull Request #352 · KSXGitHub/parallel-disk-usage

KSXGitHub · 2026-03-11T10:55:54Z

Summary

Fixes virtual block devices (VirtIO, Xen, Hyper-V, VMware) on Linux being misclassified as HDDs. The kernel's rotational sysfs flag defaults to 1 for virtual devices, causing sysinfo to report them as HDDs. This PR checks the block device's driver via /sys/block/<dev>/device/driver and reclassifies known virtual drivers as DiskKind::Unknown(-1).

Key Changes

Replaced Api trait with DiskApi (&self methods, impl'd directly on disk types) + FsApi (static filesystem operations) for fine-grained test mocking
Added reclassify_virtual_hdd() — checks sysfs driver and reclassifies virtual devices (Linux-only; no-op on other platforms)
Added extract_block_device_name() — resolves /dev/mapper/, /dev/root symlinks and parses device paths (sd*, vd*, xvd*, nvme*, mmcblk*)
Added is_virtual_block_device() — matches drivers: virtio_blk, xen_blkfront, xen-blkfront, vbd, vmw_pvscsi, hv_storvsc
Changed path_is_in_hdd to filter by mount point first, then check disk kind
Known limitation: LVM/device-mapper (/dev/dm-*) volumes are not traced to backing devices

https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

The sysinfo crate reads /sys/block/*/queue/rotational to determine disk type, but virtual block devices (VirtIO, Xen, VMware PVSCSI, Hyper-V) default to rotational=1 because the kernel doesn't know the backing storage type. This caused pdu to falsely detect virtual disks as HDDs and unnecessarily limit threads to 1. The fix adds a secondary check on Linux: when sysinfo reports HDD, we read the block device's driver via /sys/block/<dev>/device/driver and reclassify known virtual drivers (virtio_blk, xen_blkfront, vmw_pvscsi, hyperv_storvsc) as Unknown instead of HDD. https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

Apply rustfmt formatting and replace map_or with is_some_and per clippy. https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

Copilot

Pull request overview

This PR adjusts HDD detection on Linux to avoid misclassifying virtual block devices as HDDs when sysinfo reports DiskKind::HDD due to the kernel’s rotational=1 default on some virtual devices.

Changes:

Intercept DiskKind::HDD on Linux and reclassify known virtual block-device drivers to DiskKind::Unknown(-1).
Add Linux-only helpers to extract a base block device name and check the sysfs driver symlink.
Add Linux-specific tests for device-name extraction and virtual-driver detection.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
src/app/hdd.rs	Adds Linux-only correction path for HDD detection via `/sys/block/<dev>/device/driver`, plus device-name extraction.
src/app/hdd/test.rs	Adds Linux-only tests around extraction and virtual device detection (currently environment-dependent).

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src/app/hdd.rs

src/app/hdd/test.rs

- Fix Hyper-V driver name: use 'hv_storvsc' (actual kernel name) instead of 'hyperv_storvsc' - Split extract_block_device_name into parse_block_device_name (pure parsing, no I/O) and validate_block_device (sysfs check), making the parsing logic independently testable - Update doc comments to document /dev/root handling - Make tests hermetic: test_parse_block_device_name asserts deterministically on all cases without depending on sysfs availability - Improve test_extract_and_check_real_disks to validate all disk types, not just VirtIO https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

On macOS and FreeBSD, sysinfo reports DiskKind::Unknown because there is no reliable OS API for rotational vs solid-state detection. The HDD code path is never reached on those platforms today. Added a doc comment explaining this and noting the fragility if sysinfo improves detection. https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

The Api trait's purpose is to enable dependency injection by delegating to sysinfo::Disk methods. get_disk_kind should only call disk.kind(), not apply platform-specific corrections. - RealApi::get_disk_kind now purely delegates to disk.kind() - Added get_disk_name to Api trait (delegates to disk.name()) - correct_hdd_detection takes (DiskKind, &str) instead of &Disk - Correction is applied in new is_in_hdd helper called from path_is_in_hdd - Updated MockedApi to implement get_disk_name https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

The value passed (e.g. `/dev/vda1`) is a device path forwarded to `reclassify_virtual_hdd` as `disk_name`, not a filesystem mount point. Rename the macro parameter and doc string to match. https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

Add the hyphenated `virtio-blk` driver name alongside the existing `virtio_blk` for consistency with the Xen dual-name treatment. Add a comment clarifying why the recursive `extract_block_device_name` call is safe (canonicalize resolves all symlinks). https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

Replace all occurrences of `DiskKind::Unknown(-1)` with a named constant to make the intent explicit and avoid coupling to a specific numeric value across implementation and tests. https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

…ariable `is_in_hdd` checks whether a disk IS an HDD, not whether something is IN an HDD — rename to `is_hdd`. Also rename the leftover `$mount` macro capture variable to `$disk_name` to match its parameter name. https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

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Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

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src/app/hdd/test_linux_smoke.rs

+use super::{extract_block_device_name, is_virtual_block_device, RealFs};
+
+/// On hosts with a `/sys/block/vda` device, exercises the detection
+/// pipeline without panicking. Silently skips if `vda` does not exist.
+#[test]
+fn real_sysfs_vda_does_not_panic() {
+    if std::path::Path::new("/sys/block/vda").exists() {
+        let _ = is_virtual_block_device::<RealFs>("vda");
+    }
+}
+
+/// A non-existent device name must return `false` without panicking.
+#[test]
+fn nonexistent_device_is_not_virtual() {
+    assert!(
+        !is_virtual_block_device::<RealFs>("nonexistent_device_xyz"),
+        "non-existent device should not be detected as virtual"
+    );
+}
+
+/// Runs the full detection pipeline on every mounted disk.
+///
+/// Does **not** assert any specific virtual/non-virtual classification
+/// because the result depends on the host hardware. Only verifies that
+/// the pipeline completes without panicking.
+#[test]
+fn full_pipeline_does_not_panic() {
+    use sysinfo::Disks;
+    let disks = Disks::new_with_refreshed_list();
+    for disk in disks.list() {
+        let name = disk.name().to_str().unwrap_or_default();
+        if let Some(block_dev) = extract_block_device_name::<RealFs>(name) {
+            let _ = is_virtual_block_device::<RealFs>(&block_dev);
+        }
+    }
+}


src/app/hdd/test_linux_smoke.rs

+        let name = disk.name().to_str().unwrap_or_default();
+        if let Some(block_dev) = extract_block_device_name::<RealFs>(name) {


src/app/hdd.rs

+                | "vmw_pvscsi"
+                | "hv_storvsc"


…names https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

Copilot

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Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

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KSXGitHub requested a review from Copilot March 11, 2026 10:55

Copilot started reviewing on behalf of KSXGitHub March 11, 2026 10:56 View session

Fix formatting and clippy lint in HDD detection code

61aded0

Apply rustfmt formatting and replace map_or with is_some_and per clippy. https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

Copilot AI reviewed Mar 11, 2026

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claude and others added 22 commits March 11, 2026 12:12

docs: remove unneeded assertion message

2ad8c58

test: use pretty_assertions

1e8fe63

perf: reduce allocations

9f1a836

refactor: better naming convention

8bbe578

refactor: remove unneeded import and qualification

d0ccc83

refactor: use names that make more sense

299fdcf

refactor: rearrange

827342f

docs: remove commented-out code

d19d21a

refactor: rearrange

9429d33

docs: add some notes

30899e9

refactor: one-liner

06b26e4

refactor: use pipe

9993b85

docs: explain the reason for allocation

310a277

docs: add some notes

aa790f3

docs: add some notes

30e3bde

refactor: stop qualifying

c944704

refactor: replace lambda with function name

003edbc

refactor: remove unnecessary unwrap_or_default

f04425b

docs: question the AI

c92eaab

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KSXGitHub and others added 2 commits March 16, 2026 03:46

style: remove an unclean trailing comma

85a8df7

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

KSXGitHub requested a review from Copilot March 15, 2026 20:51

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refactor: replace lambda with function name

34c6538

KSXGitHub requested a review from Copilot March 15, 2026 21:13

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claude added 2 commits March 15, 2026 21:24

KSXGitHub requested a review from Copilot March 15, 2026 21:28

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claude added 2 commits March 15, 2026 21:35

docs(hdd): fix stale is_in_hdd reference in doc comment

d5f6879

https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

style(hdd): add missing space after = in macro invocations

48b844b

https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

KSXGitHub requested a review from Copilot March 15, 2026 21:36

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Copilot AI reviewed Mar 15, 2026

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refactor: replace lambda with function name

504996c

KSXGitHub requested a review from Copilot March 15, 2026 21:55

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claude added 2 commits March 15, 2026 22:12

refactor(hdd): rename single-letter closure variables to descriptive …

f8bf605

…names https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

refactor(hdd): rename driver tuple bindings to drv_path/drv_name

1add205

https://claude.ai/code/session_01MHKaZm6DcA9kjBPnW3KN5K

KSXGitHub requested a review from Copilot March 15, 2026 22:20

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fix: false hdd detection on virtual devices#352

fix: false hdd detection on virtual devices#352
KSXGitHub wants to merge 81 commits intoKSXGitHub:masterfrom
khai-slop-labs:claude/fix-hdd-detection-OQvIf

KSXGitHub commented Mar 11, 2026 •

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		let name = disk.name().to_str().unwrap_or_default();
		if let Some(block_dev) = extract_block_device_name::<RealFs>(name) {

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KSXGitHub commented Mar 11, 2026 •

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