Add File hard link API and tests #120041

SadPencil · 2025-09-24T13:11:55Z

Introduce File.CreateHardLink and FileSystemInfo.CreateAsHardLink APIs to create hard links, with platform-specific implementations. Add comprehensive tests for hard link creation, behavior, and error cases for both File and FileInfo.

Implements and closes #69030

Introduce `File.CreateHardLink` and `FileSystemInfo.CreateAsHardLink` APIs to create hard links, with platform-specific implementations. Add comprehensive tests for hard link creation, behavior, and error cases for both File and FileInfo. Implements dotnet#69030

SadPencil · 2025-09-24T13:14:02Z

@dotnet-policy-service agree

src/coreclr/nativeaot/System.Private.CoreLib/src/CompatibilitySuppressions.xml

This reverts commit e2dc032.

This reverts commit 8d8b8dd.

Copilot

Pull Request Overview

This pull request adds hard link creation APIs to .NET, implementing File.CreateHardLink and FileSystemInfo.CreateAsHardLink methods with platform-specific implementations for Windows and Unix systems.

Key changes:

Introduce public APIs for creating hard links in both File and FileSystemInfo classes
Add platform-specific implementations using Windows Kernel32 and Unix system calls
Implement comprehensive test coverage for hard link functionality

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/libraries/System.Runtime/ref/System.Runtime.cs	Add public API signatures for CreateHardLink methods
src/libraries/System.Private.CoreLib/src/System/IO/File.cs	Implement File.CreateHardLink static method
src/libraries/System.Private.CoreLib/src/System/IO/FileSystemInfo.cs	Implement CreateAsHardLink instance method
src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Windows.cs	Windows-specific hard link implementation using Kernel32
src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Unix.cs	Unix-specific hard link implementation using link system call
src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems	Add Windows interop reference for CreateHardLink
src/libraries/Common/tests/System/IO/ReparsePointUtilities.cs	Add hard link test utilities and capability detection
src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/Base/HardLinks/BaseHardLinks.FileSystem.cs	Base test class with common hard link test scenarios
src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/File/HardLinks.cs	Tests for File.CreateHardLink API
src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/FileInfo/HardLinks.cs	Tests for FileInfo.CreateAsHardLink API
src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/System.IO.FileSystem.Tests.csproj	Add test files to project compilation

src/libraries/System.Private.CoreLib/src/System/IO/FileSystemInfo.cs

src/libraries/Common/tests/System/IO/ReparsePointUtilities.cs

Co-authored-by: Copilot <[email protected]>

No functional changes.

Calling `File.WriteAllText` (creates the file if it does not exist) right after `CreateFile` might be redundant

SadPencil · 2025-10-10T08:40:31Z

Hi. May I ask the current review status of this PR?

jozkee · 2025-10-10T15:25:44Z

src/libraries/System.Private.CoreLib/src/System/IO/FileSystemInfo.cs

+        /// <summary>
+        /// Creates a hard link located in <see cref="FullName"/> that refers to the same file content as <paramref name="pathToTarget"/>.
+        /// </summary>
+        /// <param name="pathToTarget">The path of the hard link target.</param>
+        /// <exception cref="ArgumentNullException"><paramref name="pathToTarget"/> is <see langword="null"/>.</exception>
+        /// <exception cref="ArgumentException"><paramref name="pathToTarget"/> is empty.
+        /// -or-
+        /// This instance was not created passing an absolute path.
+        /// -or-
+        /// <paramref name="pathToTarget"/> contains invalid path characters.</exception>
+        /// <exception cref="IOException">A file or directory already exists in the location of <see cref="FullName"/>.
+        /// -or-
+        /// An I/O error occurred.</exception>
+        public void CreateAsHardLink(string pathToTarget)
+        {
+            FileSystem.VerifyValidPath(pathToTarget, nameof(pathToTarget));
+            FileSystem.CreateHardLink(OriginalPath, pathToTarget);
+        }


This should be in FileInfo, otherwise it will show up in DirectoryInfo too.

Thanks. Addressed in a175919

...s/System.Runtime/tests/System.IO.FileSystem.Tests/Base/HardLinks/BaseHardLinks.FileSystem.cs

jozkee · 2025-10-10T15:49:49Z

src/libraries/Common/tests/System/IO/ReparsePointUtilities.cs

    });

+    /// <summary>Creates a hard link using command line tools.</summary>
+    public static bool CreateHardLink(string linkPath, string targetPath)


Suggested change

public static bool CreateHardLink(string linkPath, string targetPath)

private static bool CreateHardLink(string linkPath, string targetPath)

In this MountHelper class (only used in System.IO.FileSystem.Tests assembly), CreateSymbolicLink and CreateJunction methods are already claimed in public. Do I still need to introduce this CreateHardLink method as a private one? It will introduce a little bit of inconsistency.

runtime/src/libraries/Common/tests/System/IO/ReparsePointUtilities.cs

Line 69 in 0edefd0

public static bool CreateSymbolicLink(string linkPath, string targetPath, bool isDirectory)

src/libraries/System.Private.CoreLib/src/System/IO/File.cs

jozkee · 2025-10-10T16:09:32Z

src/libraries/System.Private.CoreLib/src/System/IO/File.cs

+        /// <paramref name="path"/> or <paramref name="pathToTarget"/> contains a null character.</exception>
+        /// <exception cref="IOException">A file or directory already exists in the location of <paramref name="path"/>.
+        /// -or-
+        /// An I/O error occurred.</exception>


Can you please also document the FileNotFoundException thrown in CreateHardLink_TargetDoesNotExist_Throws.

FileNotFoundException is a subclass of IOException. It might be weird to mention FileNotFoundException in parallel with IOException?

Co-authored-by: David Cantú <[email protected]>

This reverts commit c43c1c1.

SadPencil · 2025-10-11T07:01:17Z

@jozkee Thanks for your review! I have addressed all your comments. Most comments are directly addressed, while I left this comment and that comment unchanged with defenses.

src/libraries/System.Runtime/ref/System.Runtime.cs

github-actions bot added the area-System.IO label Sep 24, 2025

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Sep 24, 2025

SadPencil added 2 commits September 24, 2025 21:49

Update CompatibilitySuppressions.xml to suppress APICompat

8d8b8dd

Have to include unrelated suppressions as well

e2dc032

jkotas reviewed Sep 24, 2025

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src/coreclr/nativeaot/System.Private.CoreLib/src/CompatibilitySuppressions.xml Outdated Show resolved Hide resolved

SadPencil added 4 commits September 25, 2025 00:23

Revert "Have to include unrelated suppressions as well"

eb72e2a

This reverts commit e2dc032.

Revert "Update CompatibilitySuppressions.xml to suppress APICompat"

a1d1196

This reverts commit 8d8b8dd.

Correct the expected exception in the hardlink test

944df06

Add CreateHardLink to ref

aa42eb4

build-analysis bot mentioned this pull request Sep 24, 2025

Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. dotnet/dnceng#5922

Open

3 tasks

SadPencil mentioned this pull request Sep 24, 2025

Enhance documentation on updating reference source for new APIs #120062

Merged

SadPencil marked this pull request as ready for review September 24, 2025 17:17

Copilot AI review requested due to automatic review settings September 24, 2025 17:17

Copilot AI reviewed Sep 24, 2025

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src/libraries/System.Private.CoreLib/src/System/IO/FileSystemInfo.cs Outdated Show resolved Hide resolved

src/libraries/Common/tests/System/IO/ReparsePointUtilities.cs Outdated Show resolved Hide resolved

Address incorrect comment

5536a86

Co-authored-by: Copilot <[email protected]>

SadPencil added 5 commits September 25, 2025 08:50

Reorder code blocks

941730d

No functional changes.

Merge branch 'main' into feat-io-hardlink

5029136

Slightly update the hard link test

ea28a89

Calling `File.WriteAllText` (creates the file if it does not exist) right after `CreateFile` might be redundant

Add mount helper assert to the base hard link test class

613d944

Merge branch 'main' into feat-io-hardlink

1ad09a8

build-analysis bot mentioned this pull request Sep 25, 2025

Unable to pull image from mcr.microsoft.com #117164

Open

SadPencil requested a review from jkotas September 26, 2025 14:31

jkotas requested review from a team and removed request for jkotas September 26, 2025 14:43

jozkee requested changes Oct 10, 2025

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jozkee added the needs-author-action An issue or pull request that requires more info or actions from the author. label Oct 10, 2025

Apply suggestion from @jozkee

c43c1c1

Co-authored-by: David Cantú <[email protected]>

dotnet-policy-service bot removed the needs-author-action An issue or pull request that requires more info or actions from the author. label Oct 11, 2025

SadPencil and others added 7 commits October 11, 2025 13:56

Apply suggestion from @jozkee

12ab897

Co-authored-by: David Cantú <[email protected]>

Apply suggestion from @jozkee

df34da9

Co-authored-by: David Cantú <[email protected]>

Apply suggestion from @jozkee

8b1bdbb

Co-authored-by: David Cantú <[email protected]>

Add CreateHardLink_LinkPathAlreadyExists_Throws test

f374e8c

Move CreateAsHardLink method from FileSystemInfo to FileInfo

a175919

Remove GetFileSystemInfo method in FileInfo_HardLinks test

b70714f

Revert "Apply suggestion from @jozkee"

2e39f9b

This reverts commit c43c1c1.

SadPencil requested a review from jozkee October 11, 2025 07:01

This was referenced Oct 11, 2025

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

Open

Assert Interop.Sys.LSeek(this, 0, Interop.Sys.SeekWhence.SEEK_CUR) >= 0 in System.Net.XXX tests #120577

Closed

jkotas reviewed Oct 11, 2025

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src/libraries/System.Runtime/ref/System.Runtime.cs Outdated Show resolved Hide resolved

SadPencil added 2 commits October 12, 2025 00:04

Sort the CreateAsHardLink method in the ref file of System.Runtime

eb318f3

Merge branch 'main' into feat-io-hardlink

d6863ec

	public static bool CreateHardLink(string linkPath, string targetPath)
	private static bool CreateHardLink(string linkPath, string targetPath)

Add File hard link API and tests #120041

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Add File hard link API and tests #120041

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