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CreateDirectory: eliminate some syscalls. #58799

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merged 4 commits into from
Nov 18, 2021
Merged

CreateDirectory: eliminate some syscalls. #58799

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80ea5f9
CreateDirectory: eliminate some syscalls.
tmds Sep 8, 2021
1543497
Explicitly handle '/'.
tmds Sep 8, 2021
7b08a5f
cleanup
tmds Sep 8, 2021
0a03e35
PR feedback
tmds Nov 18, 2021
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156 changes: 86 additions & 70 deletions src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Unix.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -272,101 +272,117 @@ public static void DeleteFile(string fullPath)

public static void CreateDirectory(string fullPath)
{
// NOTE: This logic is primarily just carried forward from Win32FileSystem.CreateDirectory.
// The argument is a full path, which means it is an absolute path that
// doesn't contain "//", "/./", and "/../".
Debug.Assert(fullPath.Length > 0);
Debug.Assert(PathInternal.IsDirectorySeparator(fullPath[0]));

int length = fullPath.Length;

// We need to trim the trailing slash or the code will try to create 2 directories of the same name.
if (length >= 2 && Path.EndsInDirectorySeparator(fullPath))
if (fullPath.Length == 1)
{
length--;
return; // fullPath is '/'.
}

// For paths that are only // or ///
if (length == 2 && PathInternal.IsDirectorySeparator(fullPath[1]))
int result = Interop.Sys.MkDir(fullPath, (int)Interop.Sys.Permissions.Mask);
if (result == 0)
{
throw new IOException(SR.Format(SR.IO_CannotCreateDirectory, fullPath));
return; // Created directory.
}

// We can save a bunch of work if the directory we want to create already exists.
if (DirectoryExists(fullPath))
Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
if (errorInfo.Error == Interop.Error.EEXIST && DirectoryExists(fullPath))
{
return;
return; // Path already exists and it's a directory.
}
else if (errorInfo.Error == Interop.Error.ENOENT)
{
// Some parts of the path don't exist yet.
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CreateParentsAndDirectory(fullPath);
}
else
{
throw Interop.GetExceptionForIoErrno(errorInfo, fullPath, isDirectory: true);
}
}

// Attempt to figure out which directories don't exist, and only create the ones we need.
bool somepathexists = false;
public static void CreateParentsAndDirectory(string fullPath)
{
// Try create parents bottom to top and track those that could not
// be created due to missing parents. Then create them top to bottom.
List<string> stackDir = new List<string>();
int lengthRoot = PathInternal.GetRootLength(fullPath);
if (length > lengthRoot)

stackDir.Add(fullPath);

int i = fullPath.Length - 1;
// Trim trailing separator.
if (PathInternal.IsDirectorySeparator(fullPath[i]))
{
i--;
}
do
{
int i = length - 1;
while (i >= lengthRoot && !somepathexists)
// Find the end of the parent directory.
Debug.Assert(!PathInternal.IsDirectorySeparator(fullPath[i]));
while (!PathInternal.IsDirectorySeparator(fullPath[i]))
{
if (!DirectoryExists(fullPath.AsSpan(0, i + 1))) // Create only the ones missing
{
stackDir.Add(fullPath.Substring(0, i + 1));
}
else
{
somepathexists = true;
}

while (i > lengthRoot && !PathInternal.IsDirectorySeparator(fullPath[i]))
{
i--;
}
i--;
}
}

int count = stackDir.Count;
if (count == 0 && !somepathexists)
{
ReadOnlySpan<char> root = Path.GetPathRoot(fullPath.AsSpan());
if (!DirectoryExists(root))
// Try create it.
string mkdirPath = fullPath.Substring(0, i);
int result = Interop.Sys.MkDir(mkdirPath, (int)Interop.Sys.Permissions.Mask);
if (result == 0)
{
throw Interop.GetExceptionForIoErrno(Interop.Error.ENOENT.Info(), fullPath, isDirectory: true);
// Created parent.
break;
}
return;
}

// Create all the directories
int result = 0;
Interop.ErrorInfo firstError = default(Interop.ErrorInfo);
string errorString = fullPath;
for (int i = stackDir.Count - 1; i >= 0; i--)
{
string name = stackDir[i];
Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
if (errorInfo.Error == Interop.Error.ENOENT)
{
// Some parts of the path don't exist yet.
// We'll try to create its parent on the next iteration.

// The mkdir command uses 0777 by default (it'll be AND'd with the process umask internally).
// We do the same.
result = Interop.Sys.MkDir(name, (int)Interop.Sys.Permissions.Mask);
if (result < 0 && firstError.Error == 0)
// Track this path for later creation.
stackDir.Add(mkdirPath);
}
else if (errorInfo.Error == Interop.Error.EEXIST)
{
Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
// Parent exists.
// If it is not a directory, MkDir will fail when we create a child directory.
break;
}
else
{
throw Interop.GetExceptionForIoErrno(errorInfo, mkdirPath, isDirectory: true);
}
i--;
} while (i > 0);

// While we tried to avoid creating directories that don't
// exist above, there are a few cases that can fail, e.g.
// a race condition where another process or thread creates
// the directory first, or there's a file at the location.
if (errorInfo.Error != Interop.Error.EEXIST)
{
firstError = errorInfo;
}
else if (FileExists(name) || (!DirectoryExists(name, out errorInfo) && errorInfo.Error == Interop.Error.EACCES))
// Create directories that had missing parents.
for (i = stackDir.Count - 1; i >= 0; i--)
{
string mkdirPath = stackDir[i];
int result = Interop.Sys.MkDir(mkdirPath, (int)Interop.Sys.Permissions.Mask);
if (result < 0)
{
Interop.ErrorInfo errorInfo = Interop.Sys.GetLastErrorInfo();
if (errorInfo.Error == Interop.Error.EEXIST)
{
// If there's a file in this directory's place, or if we have ERROR_ACCESS_DENIED when checking if the directory already exists throw.
firstError = errorInfo;
errorString = name;
// Path was created since we last checked.
// Continue, and for the last item, which is fullPath,
// verify it is actually a directory.
if (i != 0)
{
continue;
}
if (DirectoryExists(mkdirPath))
{
return;
}
}
}
}

// Only throw an exception if creating the exact directory we wanted failed to work correctly.
if (result < 0 && firstError.Error != 0)
{
throw Interop.GetExceptionForIoErrno(firstError, errorString, isDirectory: true);
throw Interop.GetExceptionForIoErrno(errorInfo, mkdirPath, isDirectory: true);
}
}
}

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