Cannot change LastWriteTime or LastAccessTime of a symlink #38824
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Dotnet-GitSync-Bot
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I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label. |
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@jeffschwMSFT this doesn't seem related to Setup, can you reassign to FileSystem owners? |
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@Liturgist, allow me to provide a more succinct repro: Run either in PowerShell [Core] v6+ or in Windows PowerShell, in which case the session must be elevated: # Create a test target file.
$null > tmp.txt
# Create a symlink to it.
$link = New-Item -Force -ItemType SymbolicLink tmpL.txt -Target tmp.txt
# Try to modify the *symlink*'s LastWriteTime.
$link.LastWriteTime = '2020-01-01'
# List both the link and the target, which shows that the *target*'s
# LastWriteTime was modified.
Get-Item tmp.txt, tmpL.txt -OutVariable result
# Clean up.
$result | Remove-ItemIn PowerShell Core, you'll get output such as the following, showing that the target was modified, not the link itself: See also: The proposed symlink API in #24271 |
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Thanks for the details. I know in Linux, there are ways to manipulate the attributes of the symbolic link itself, For example you can read the file attributes using What I would like to investigate is if Windows has similar options to modify symbolic link attributes. I know the Windows methods to create symbolic links, but I can't find a method to edit an existing symbolic link. @Liturgist can you share more information about why you want to edit the symbolic link attributes, and specifically, the timestamps? |
carlossanlop
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@carlossanlop I've implemented fixes for this in #49555. |
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Thank you so much for offering your help, @hamarb123 ! I assigned this issue to you per your request. I'm looking forward to reviewing your PR. |
ghost
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Just to clarify my reasoning as to why I think we should proceed with the changes in #49555 and #52639 (setting it on the reparse point itself) is because (in no particular order):
This is why I think we should set and get from the link itself in my opinion. |
ghost
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…#52639) * Implement most of the fix for #38824 Reverts the changes in the seperate PR a617a01 to fix #38824. Does not re-enable the test because that relies on #49555, will add a seperate commit to whichever is merged last to enable the SettingUpdatesPropertiesOnSymlink test. * Most of the code for PR #52639 to fix #38824 • Deal with merge conflicts • Add FSOPT_NOFOLLOW for macOS and use it in setattrlist • Use AT_SYMLINK_NOFOLLOW with utimensat (note: there doesn't seem to be an equivalent for utimes) • Add SettingUpdatesPropertiesOnSymlink test to test if it actually sets it on the symlink itself (to the best that we can anyway ie. write + read the times) • Specify FILE_FLAG_OPEN_REPARSE_POINT for CreateFile in FileSystem.Windows.cs (is there any other CreateFile calls that need this?) * Remove additional FILE_FLAG_OPEN_REPARSE_POINT I added FILE_FLAG_OPEN_REPARSE_POINT before and it was then added in another PR, this removes the duplicate entry. * Add missing override keywords Add missing override keywords for abstract members in the tests. * Fix access modifiers Fix access modifiers for tests - were meant to be protected rather than public * Add more symlink tests, rearrange files • Move symlink creation api to better spot in non-base files • Add IsDirectory property for some of the new tests • Change abstract symlink api to CreateSymlink that accepts path and target • Create a CreateSymlinkToItem method that creates a symlink to an item that may be relative that uses the new/modified abstract CreateSymlink method • Add SettingUpdatesPropertiesCore to avoid code duplication • Add tests for the following variants: normal/symlink, target exists/doesn't exist, absolute/relative target • Exclude nonexistent symlink target tests on Unix for Directories since they are counted as files * Fix return type of CreateSymlink in File/GetSetTimes.cs * Remove browser from new symlink tests as it doesn't support creation of symlinks Remove browser from new symlink tests as it doesn't support creation of symlinks * Use lutimes, improve code readability, simplify tests • Use lutimes when it's available • Extract dwFlagsAndAttributes to a variable • Use same year for all tests • Checking to delete old symlink is unnecessary, so don't • Replace var with explicit type * Change year in test to 2014 to reduce diff * Rename symlink tests, use 1 core symlink times function, and check that target times don't change Rename symlink tests, use 1 core symlink times function, and check that target times don't change * Inline RunSymlinkTestPart 'function' Inline RunSymlinkTestPart 'function' so that the code can be reordered so the access time test can be valid. * Share CreateSymlinkToItem call in tests and update comment for clarity * Update symlink time tests • Make SettingUpdatesPropertiesOnSymlink a theory • Remove special case for Unix due to #52639 (comment) (will revert if fails) • Rename isRelative to targetIsRelative for clarity * Remove unnecessary Assert.All * Changes to SettingUpdatesPropertiesOnSymlink test • Rename item field to link field • Don't use if one-liner • Use all time functions since only using UTC isn't necessary • Remove the now-defunct IsDirectory property since we aren't checking it anymore * Remove unnecessary fsi.Refresh() • Remove unnecessary fsi.Refresh() since atime is only updated when reading a file * Updates to test and pal_time.c • Remove targetIsRelative cases • Multi-line if statement • Combine HAVE_LUTIMES and #else conditions to allow more code charing * Remove trailing space
ghost
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Is there a quick workaround for |
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You can use the pinvokes yourself to write a function that updates the symlink rather than the target, for Windows that would be: using Microsoft.Win32.SafeHandles;
using System.ComponentModel;
using System.Runtime.InteropServices;
const int FileBasicInfo = 0;
SafeFileHandle handle =
CreateFilePrivate(
"C:/your-link",
0x40000000 /* Write */,
FileShare.ReadWrite | FileShare.Delete,
lpSecurityAttributes: 0,
FileMode.Open,
0x00200000 /* Open reparse point */,
IntPtr.Zero);
var basicInfo = new FILE_BASIC_INFO()
{
CreationTime = -1,
LastAccessTime = -1,
LastWriteTime = DateTime.UtcNow.AddDays(1).ToFileTime(),
ChangeTime = -1,
FileAttributes = 0
};
unsafe
{
if (!SetFileInformationByHandle(handle, FileBasicInfo, &basicInfo, (uint)sizeof(FILE_BASIC_INFO)))
{
throw new Win32Exception(Marshal.GetLastWin32Error());
}
}
Console.WriteLine("Success!");
// interop code:
[DllImport("kernel32.dll", EntryPoint = "CreateFileW", CharSet = CharSet.Unicode, ExactSpelling = true, SetLastError = true)]
static unsafe extern SafeFileHandle CreateFilePrivate(
string lpFileName,
int dwDesiredAccess,
FileShare dwShareMode,
uint lpSecurityAttributes,
FileMode dwCreationDisposition,
int dwFlagsAndAttributes,
IntPtr hTemplateFile);
[DllImport("kernel32.dll", ExactSpelling = true, SetLastError = true)]
static unsafe extern bool SetFileInformationByHandle(
SafeFileHandle hFile,
int FileInformationClass,
void* lpFileInformation,
uint dwBufferSize);
struct FILE_BASIC_INFO
{
internal long CreationTime;
internal long LastAccessTime;
internal long LastWriteTime;
internal long ChangeTime;
internal uint FileAttributes;
}You can expand above code to also work with other OSes by looking at what .NET uses internally. |
ghost
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Description
It does not appear to be possible to change the LastWriteTime or LastAccessTime of a symlink. It works on hardlinks.
Configuration
Regression?
Unknown
Other information
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