SQL Server: xp_fileexist and UNC path permissions

问题

I'm attempting to run an ad hoc query in SQL Server Management Studio that uses the undocumented stored procedure xp_fileexist. I want to test for the existence of files in a subfolder under a network shared folder accessed via a UNC path.

Here's a sqlservercentral post that talks about the execution context of xp_fileexist. From what I can tell I've got all the necessary permissions in place:

• I'm running SQL Server Management Studio from a domain account that has Full Control of the shared folder and its subfolders.
• The SQL account is linked to the domain account and has the sysadmin role.
• The SQL Server service logs on as Network Service.
• Network Service has Full Control of the shared folder and its subfolders.

I'm concerned that some of these permission settings might be overkill, yet xp_fileexist still cannot see the subfolder contents.

EXEC master.dbo.xp_fileexist '\\servername\sharename\subfolder\filename.txt'

File Exists |File is a Directory |Parent Directory Exists
---------------------------------------------------------
0           |0                   |0

But xp_fileexist does see the shared folder itself.

EXEC master.dbo.xp_fileexist '\\servername\sharename'

File Exists |File is a Directory |Parent Directory Exists
---------------------------------------------------------
0           |1                   |1

Questions:

Why are the shared folder's contents invisible?

And what security settings are actually necessary?

来源：https://stackoverflow.com/questions/12100845/sql-server-xp-fileexist-and-unc-path-permissions