Implement SunOS FileSystemWatcher using portfs event ports by gwr · Pull Request #124716 · dotnet/runtime

gwr · 2026-02-22T01:54:47Z

This implementation uses SunOS portfs (event ports) to watch for directory changes. Unlike Linux inotify, portfs can only detect WHEN a directory changes, not WHAT changed. Therefore, this implementation:

Maintains a snapshot of each watched directory's contents
When portfs signals a change, re-reads the directory
Compares new vs old snapshots to detect creates/deletes/modifications
Generates appropriate FileSystemWatcher events

Key implementation details:

Uses pinned GC.AllocateArray for file_obj structures required by portfs
When watching attributes or timestamps watches directory contents too
Each watched objct gets a unique cookie for identification
port_get returns the cookie to indicate which object changed
Optimized snapshot comparison with sorted single-pass algorithm
Supports IncludeSubdirectories by recursively watching child directories
Track mtime of the watched directory to avoid missing changes
Implement graceful cancellation using PortSend

Native changes (pal_io.c):

SystemNative_PortCreate: Opens event port file descriptor
SystemNative_PortAssociate: Associates directory with port using file_obj
SystemNative_PortGet: Waits for events, returns cookie identifying directory
SystemNative_PortSend: Send an event (used in cancellation)
SystemNative_PortDissociate: Removes directory association

Performance notes:

Less efficient than inotify (must re-read directories on each change)
Better than polling (blocks until change occurs)
Memory overhead for directory snapshots

Passes all System.IO.FileSystem.Watcher.Tests

dotnet-policy-service · 2026-02-22T01:55:50Z

Tagging subscribers to this area: @dotnet/area-system-io
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Copilot

Pull request overview

This PR implements FileSystemWatcher support for SunOS (Solaris/illumos) using the portfs (event ports) API. Unlike Linux's inotify which reports specific file changes, portfs only signals that a directory has changed, requiring the implementation to maintain snapshots and perform comparisons to determine what actually changed.

Changes:

Native interop layer for portfs operations (port_create, port_associate, port_get, port_send, port_dissociate)
SunOS-specific FileSystemWatcher implementation using snapshot-based change detection
Hybrid monitoring mode that watches both directories (for name changes) and individual files (for attribute changes)
Support for recursive subdirectory monitoring with resource limits (50 subdirs, 1000 files per directory)

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 18 comments.

Show a summary per file

File	Description
src/native/libs/configure.cmake	CMake configuration for portfs feature detection (has critical bug)
src/native/libs/System.Native/pal_io.h	Header declarations for portfs native functions (has spelling errors)
src/native/libs/System.Native/pal_io.c	Native implementation of portfs wrapper functions (has critical string lifetime bug)
src/native/libs/System.Native/entrypoints.c	Export table entries for new portfs functions
src/native/libs/Common/pal_config.h.in	Configuration flag for HAVE_SUNOS_PORTFS
src/libraries/System.IO.FileSystem.Watcher/tests/System.IO.FileSystem.Watcher.Tests.csproj	Added illumos and solaris to test target frameworks
src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs	Main SunOS implementation with snapshot comparison and event generation (multiple issues)
src/libraries/System.IO.FileSystem.Watcher/src/System.IO.FileSystem.Watcher.csproj	Added SunOS-specific source files and target frameworks
src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs	Managed P/Invoke declarations for portfs (has hardcoded struct size issue)

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.h

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.c

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 13 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.c

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/configure.cmake

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 10 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.c

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.h

src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/configure.cmake

src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

src/native/libs/System.Native/pal_io.c

src/libraries/Common/src/Interop/SunOS/portfs/Interop.portfs.cs

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

The github dotnet copilot keeps misundertanding the design github.com/dotnet/pull/124716#discussion_r2838448285

Copilot

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

github.com/dotnet/pull/124716#discussion_r2838494096

gwr · 2026-02-22T22:08:56Z

Now that I seem to be caught-up with Copilot feedback, I've squashed so I can more easily cherry pick this into a local branch with other necessary fixes so I can re-test.

am11 · 2026-02-22T23:05:14Z

@tmds, could you please take a look?

Portfs is a generic I/O eventing facility in SunOS-like platforms: port_create(3C) - https://smartos.org/man/3c/port_create. I might be mistaken, but regarding time complexity: with your recent Linux inotify overhaul, the kernel:userland path is essentially O(1). On illumos/Solaris, this implemention's kernel:userland portion is O(n log n) due to the snapshot comparison required to reconstruct file-level changes. This complexity is probably unavoidable given the lack of per-file events, but (perhaps?) still better than not having any watcher support.

Copilot

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.c

src/native/libs/System.Native/pal_io.h

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

Copilot

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

src/native/libs/System.Native/pal_io.h

src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.SunOS.cs

github.com/dotnet/pull/124716#discussion_r2838974229

github.com/dotnet/pull/124716#discussion_r2838974245

github.com/dotnet/pull/124716#discussion_r2839027292

github.com/dotnet/pull/124716#discussion_r2839027304

github.com/dotnet/pull/124716#discussion_r2840704581

github.com/dotnet/pull/124716#discussion_r2840704598

github.com/dotnet/pull/124716#discussion_r2840704624

This implementation uses SunOS portfs (event ports) to watch for directory changes. Unlike Linux inotify, portfs can only detect WHEN a directory changes, not WHAT changed. Therefore, this implementation: 1. Maintains a snapshot of each watched directory's contents 2. When portfs signals a change, re-reads the directory 3. Compares new vs old snapshots to detect creates/deletes/modifications 4. Generates appropriate FileSystemWatcher events Key implementation details: - Uses pinned GC.AllocateArray for file_obj structures required by portfs - When watching attributes or timestamps watches directory contents too - Each watched objct gets a unique cookie for identification - port_get returns the cookie to indicate which object changed - Optimized snapshot comparison with sorted single-pass algorithm - Supports IncludeSubdirectories by recursively watching child directories - Track mtime of the watched directory to avoid missing changes - Implement graceful cancellation using PortSend Native changes (pal_io.c): - SystemNative_PortCreate: Opens event port file descriptor - SystemNative_PortAssociate: Associates directory with port using file_obj - SystemNative_PortGet: Waits for events, returns cookie identifying directory - SystemNative_PortSend: Send an event (used in cancellation) - SystemNative_PortDissociate: Removes directory association Performance notes: - Less efficient than inotify (must re-read directories on each change) - Better than polling (blocks until change occurs) - Memory overhead for directory snapshots Passes 99% of System.IO.FileSystem.Watcher.Tests --------- Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

gwr · 2026-02-23T15:17:16Z

Squashed the last dozen updates to simplify local testing.

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Improve design comments some more

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The github dotnet copilot keeps misundertanding the design github.com/dotnet/pull/124716#discussion_r2838448285

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Add locking around subdirectoryWatchers changes

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github.com/dotnet/pull/124716#discussion_r2838494096

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[wasm/browser] Failed to connect to socket /run/dbus/system_bus_socket #120176

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[wasm] Microsoft.Playwright.TargetClosedException : Target page, context or browser has been closed #121195

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Check for symlink in CreateSingleSubdirectoryWatcher

e0a4818

github.com/dotnet/pull/124716#discussion_r2838974229

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Need to cancel when subdir deleted

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github.com/dotnet/pull/124716#discussion_r2838974245

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Add locking around limit checks

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github.com/dotnet/pull/124716#discussion_r2839027292

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Fix possiblecancellation token leak

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github.com/dotnet/pull/124716#discussion_r2839027304

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Minor improvements, clarification comments

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github.com/dotnet/pull/124716#discussion_r2840704581

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Improve pal_io.h comments etc

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github.com/dotnet/pull/124716#discussion_r2840704598

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Improve null name defense in directory enum

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github.com/dotnet/pull/124716#discussion_r2840704624

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