Fix New-Item to create correct symlink type (#2915) by jeffbi · Pull Request #3509 · PowerShell/PowerShell

jeffbi · 2017-04-07T21:04:15Z

Fix #2915
Now creates a file symlink to a file target and to an non-existent target, and a directory symlink to a directory target.

Creating Links with New-Item

The New-Item cmdlet allows for creating file system links.
In general, New-Item can create four types of links:

Hard Link
- Created when -ItemType is HardLink
Symbolic Link
- Created when -ItemType is SymbolicLink and either the target exists and is a file, or the target does not exist
  - In Windows, if the target is a directory then New-Item -ItemType Symbolic Link will create a directory symbolic link, not a "plain" symbolic link.
  - In Linux and OS X, New-Item -ItemType Symbolic Link will always create a "plain" symbolic link, regardless of whether the target is a file or directory, or whether the target exists or not.
- In Windows, elevated privileges are required to create a symbolic link.
Directory Symbolic Link
- Created when -ItemType is SymbolicLink and the target exists and is a directory
- Supported only on NTFS file system
- In Windows, elevated privileges are required to create a directory symbolic link.
- In Linux and OS X, New-Item will not create a directory symbolic link, even on an NTFS volume.
Directory Junction
- Supported only on NTFS file system
- In Linux and OS X, New-Item will not create a directory junction, even on an NTFS volume.
  - Currently, New-Item will begin to create the junction by creating the link directory. When the attempt to turn the newly-created directory into a junction fails, New-Item will delete the new directory and silently fail.

The following table shows the types of links and targets the `New-Item` cmdlet can create on Windows:

Link Type / Target	Existing File	Existing Directory	Non-Existent	"Plain" Symbolic Link	Directory Symbolic Link	Directory Junction
Hard Link	Yes	No	No	Yes	No	No
"Plain" Symbolic Link	Yes	No¹	Yes	Yes	No¹	No¹
Directory Symbolic Link	No¹	Yes	No¹	No¹	Yes	Yes
Directory Junction	No	Yes	No	No	Yes	Yes

1 While the NTFS file system and the Windows operating system support "plain" symbolic links to existing directories and *directory* symbolic links to files and to non-existent items, the `New-Item` cmdlet cannot create them.

The following table shows the types of links and targets the `New-Item` cmdlet can create on Linux and OS X:

Link Type / Target	Existing File	Existing Directory	Non-Existent	"Plain" Symbolic Link	Directory Symbolic Link	Directory Junction
Hard Link	Yes	No	No	Yes	No	No
"Plain" Symbolic Link	Yes	Yes	Yes	Yes	No	No
Directory Symbolic Link²	No	No	No	No	No	No
Directory Junction²	No	No	No	No	No	No

2 The Linux and OS X operating systems do not support *directory* symbolic links or directory junctions.

Now creates a file symlink to a file target and to an non-existent target, and a directory symlink to a directory target. Also updated tests.

iSazonov · 2017-04-08T18:35:33Z

+        $fileInfo.Attributes -band $DirLinkMask | Should Be $DirLinkMask

        # Remove the link explicitly to avoid broken symlink issue
        Remove-Item $FullyQualifiedLink -Force


Is it still relevant?

Sorry, is what still relevant?

Here Remove-Item is workaround for a bug. Is the bug already fixed?

Ah. I didn't know what "broken symlink issue" the author was referring to, so I didn't remove another dev's code. I am working on a Remove-Item issue, but I want to get this in so I can write tests using New-Item rather than shelling out a mklink command.

I guess it's about problem with recursion when there are symlink. It is seems already fixed. It is not related with your PR.
Closed.

iSazonov · 2017-04-08T18:36:05Z

LGTM.

jeffbi · 2017-04-10T22:38:49Z

@joeyaiello, @SteveL-MSFT Can whoever else needs to review this please do so? I have another issue that is waiting on this one to finish updating its PR, then I'll likely want to use changes from that one in yet another issue.

SteveL-MSFT · 2017-04-11T23:29:16Z

cc @PowerShell/area-providers

iSazonov · 2017-04-12T04:34:26Z

@jeffbi Thanks very much for great PR description!

iSazonov · 2017-04-14T19:38:08Z

@mirichmo @SteveL-MSFT The PR block #3441. 😕 Could you please continue with the PR?

daxian-dbw · 2017-04-14T21:17:02Z

@jeffbi could you please help me to understand how the change in FileSystemProvider.cs fixed the issue?
It looks to me there is only one behavior change after the fix -- an exception will be thrown from CheckItemExists in windows, when NativeMethods.GetFileAttributes fails, and in that case, New-Item will return with an error message. It's not very obvious how this fixes the issue #2915. Could you please elaborate/explain the fix a bit?

daxian-dbw · 2017-04-14T21:21:03Z

@jeffbi Never mind, isDirectory is the key here. The change looks good.

iSazonov · 2017-04-15T09:48:01Z

@daxian-dbw Thanks for quick response!

Fix New-Item to create correct symlink type (#2915)

8085018

Now creates a file symlink to a file target and to an non-existent target, and a directory symlink to a directory target. Also updated tests.

msftclas added the cla-already-signed label Apr 7, 2017

iSazonov reviewed Apr 8, 2017

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joeyaiello mentioned this pull request Apr 10, 2017

New-Item -ItemType SymbolicLink folder cannot be opened #2915

Closed

mirichmo self-assigned this Apr 11, 2017

jeffbi mentioned this pull request Apr 14, 2017

Replace string-compare-based test for copying to same file with more … #3441

Merged

daxian-dbw merged commit 06020f3 into PowerShell:master Apr 14, 2017

jeffbi deleted the new-item-2915 branch April 24, 2017 23:22

SteveL-MSFT mentioned this pull request Apr 26, 2017

Symlinks cause weirdness related to trailing slash #1775

Closed

mklement0 mentioned this pull request Mar 6, 2019

New-Item symlinks cannot be created if destination (target) is non-existent or not accessible #9067

Closed

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jeffbi commented Apr 7, 2017 • edited by daxian-dbw Loading Uh oh! There was an error while loading. Please reload this page.

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Creating Links with New-Item

The following table shows the types of links and targets the New-Item cmdlet can create on Windows:

The following table shows the types of links and targets the New-Item cmdlet can create on Linux and OS X:

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jeffbi commented Apr 7, 2017 •

edited by daxian-dbw

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The following table shows the types of links and targets the `New-Item` cmdlet can create on Windows:

The following table shows the types of links and targets the `New-Item` cmdlet can create on Linux and OS X:

daxian-dbw commented Apr 14, 2017 •

edited

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