Is there a way to reliably detect a removed directory via SMB on Windows?

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Summary

The problem of reliably detecting a removed directory via SMB on Windows is a challenging one, especially when dealing with cached results from the Windows API. Cache bypassing is essential to get the most up-to-date information about the directory’s existence. However, as the Windows API (e.g., GetFileAttributesEx, NtQueryInformationFile) doesn’t provide a straightforward way to bypass caching, alternative approaches must be considered.

Root Cause

The root cause of this issue is the caching mechanism in the Windows API, which can return stale results. Key causes include:

  • The Windows API’s inability to bypass cache
  • SMB protocol limitations
  • File system caching mechanisms

Why This Happens in Real Systems

This problem occurs in real systems due to the following reasons:

  • Network file systems like SMB are prone to caching issues
  • Remote file operations can lead to delays in updating cache
  • Concurrent access to the same directory can cause inconsistencies

Real-World Impact

The impact of not being able to detect a removed directory includes:

  • False positives: incorrect assumptions about the directory’s existence
  • Application crashes: due to attempting to access a non-existent directory
  • Data inconsistencies: resulting from outdated cache information

Example or Code (if necessary and relevant)

#include 

int main() {
    // Attempt to get file attributes with caching
    DWORD attributes;
    if (GetFileAttributesEx("remote\\\\\\\\\\path", GetFileExInfoStandard, &attributes) == 0) {
        // Handle error
    }
    return 0;
}

How Senior Engineers Fix It

Senior engineers address this issue by:

  • Using lower-level system calls to bypass caching
  • Implementing custom caching mechanisms to track directory existence
  • Periodically refreshing cache information to ensure accuracy

Why Juniors Miss It

Juniors may overlook this issue due to:

  • Lack of understanding of caching mechanisms in Windows API
  • Insufficient experience with network file systems and SMB protocol
  • Overreliance on high-level APIs without considering low-level details