Tips/Support

  • The Old New Thing

    How do I disable zone markers for downloaded files, so that Explorer stops being a nag about running downloaded files and just trusts me to do the right thing?

    • 43 Comments

    My Little Program about manipulating the zone identifier for downloaded files appears to have struck a nerve with commenter Tess, who launched into some sort of diatribe about how Microsoft should stop being a busybody and warning users about opening files that they downloaded.

    You are welcome to disable the feature if it offends you so.

    In the Group Policy editor, go to User Configuration, Administrative Templates, Windows Components, Attachment Manager, and enable Do not preserve zone information in file attachments.

    For bonus points, you can set a bunch of other policies to make your computer even more dangerous. Here's a list of them. For example, if your goal is to create the most insecure deployment of Internet Explorer, you can set Inclusion list for moderate risk file types and Inclusion list for low risk file types both to *.*, and then on top of that, set Launching applications and unsafe files to Enabled (not secure) so that Internet Explorer never warns you about running anything.

    Welcome to 1995. Enjoy your stay.

  • The Old New Thing

    What order does the DIR command arrange files if no sort order is specified?

    • 28 Comments

    If you don't specify a sort order, then the DIR command lists the files in the order that the files are returned by the Find­First­File function.

    Um, okay, but that just pushes the question to the next level: What order does Find­First­File return files?

    The order in which Find­First­File returns files in unspecified. It is left to the file system driver to return the files in whatever order it finds most convenient.

    Now we're digging into implementation details.

    For example, the classic FAT file system simply returns the names in the order they appear on disk, and when a file is created, it is merely assigned the first available slot in the directory. Slots become available when files are deleted, and if no slots are available, then a new slot is created at the end.

    Modern FAT (is that an oxymoron?) with long file names is more complicated because it needs to find a sequence of contiguous entries large enough to hold the name of the file.

    There used to be (maybe there still are) some low-level disk management utilities that would go in and manually reorder your directory entries.

    The NTFS file system internally maintains directory entries in a B-tree structure, which means that the most convenient way of enumerating the directory contents is in B-tree order, which if you cover one eye and promise not to focus too closely looks approximately alphabetical for US-English. (It's not very alphabetical for most other languages, and it falls apart once you add characters with diacritics or anything outside of the Latin alphabet, and that includes spaces and digits!)

    The ISO 9660 file system (used by CD-ROMs) requires that directory entries be lexicographical sorted by ASCII code point. Pretty much everybody has abandoned the base ISO 9660 file system and uses one of its many extensions, such as Joliet or UDF, so you have that additional wrinkle to deal with.

    If you are talking to a network file system, then the file system on the other end of the network cable could be anything at all, so who knows what its rules are (if it even has rules).

    When people ask this question, it's usually in the context of a media-playing device which plays media from a CD-ROM or USB thumb drive in the raw native file order. But they don't ask this question right out; they ask some side question that they think will solve their problem, but they don't come out and say what their problem is.

    So let's solve the problem in context: If the storage medium is a CD-ROM or an NTFS-formatted USB thumb drive, then the files will be enumerated in sort-of-alphabetical order, so you can give your files names like 000 First track.mp3, 001 Next track.mp3, and so on.

    If the storage medium is a FAT-formatted USB thumb drive, then the files will be enumerated in a complex order based on the order in which files are created and deleted and the lengths of their names. But the easy way out is simply to remove all the files from a directory then move file files into the directory in the order you want them enumerated. That way, the first available slot is the one at the end of the directory, so the file entry gets appended.

    Of course, none of this behavior is contractual. NTFS would be completely within its rights to, for example, return entries in reverse alphabetical order on odd-numbered days. Therefore, you shouldn't write a program that relies on any particular order of enumeration. (Or even that the order of enumeration is consistent between two runs!)

  • The Old New Thing

    If you cancel an operation while it's in progress, then it's not surprising that it's only half-done

    • 65 Comments

    A customer (via their customer liaison) started by asking why they were seeing an unexpected access control entry in the security descriptor of an object.

    The ACEs on the parent grant access to Administrators, CREATOR OWNER, SYSTEM, and Users, but the ACEs on the child object (which should simply have been inherited from the parent) include an extra entry for Bob. How did Bob get access to the child object? When we view the details of the ACEs, it lists the Bob entry as Inherited from parent. But there is no Bob entry in the parent!

    I observed, "Probably because Bob is the CREATOR OWNER."

    Thanks for the explanation, but even if Bob is the CREATOR OWNER, how can we explain that the permission is inherited from the parent?

    The permission is inherited from the parent because the parent has specified the rights of the CREATOR OWNER, and Bob is the creator/owner. As part of the inheritance process, the rights of the CREATOR OWNER get assigned to Bob.

    Remember that CREATOR OWNER is not a real person. It is a placeholder that gets replaced with the actual creator/owner when the object is created. If Bob created the child object, then the permissions of CREATOR OWNER will be given to Bob on the child object.

    The CREATOR OWNER is not a live entry that dynamically updates to match the current creator/owner. It is a static entry that is assigned at the point of creation. Changes to the owner in the future have no effect because the identity has already been snapshotted. (I think a less confusing name would have been simply OBJECT CREATOR, since creation happens only once.)

    (Note that there is a little extra weirdness here: If the creator is a member of the Administrators group, then the CREATOR OWNER rights get assigned to the entire Administrators group instead of the specific user who created it. You can change this behavior by tweaking the Default owner for objects created by members of the Administrators group policy.)

    The customer liaison conferred with the customer, and determined that, at least in one of the cases they were studying, Bob was not the original creator.

    What actually happened was that at some point, Bob was granted access to the parent object and all its sub-objects. Later, somebody went back to the parent object and told it to revoke Bob's access to the parent object and all its sub-objects. But "If we cancel the process fast enough, then we get the strange behavior as originally described."

    Well, duh!

    You asked for Bob's access to the parent object and all its sub-objects to be revoked, so the tool you used started a recursive tree walk from the parent object looking for any objects that Bob has access to and removing them. But if you cancel the operation partway through, then that tool didn't get a chance to finish the job, and you obviously are left in a situation where Bob's access was only partially revoked.

    The customer liaison confirmed,

    Yes, that's what happened.

    It's nice of the customer liaison to confirm the diagnosis, but it still baffles me that they were confused by this in the first place.

    To me this is one of those So what did you expect type of situations. You start an operation, then partway through, you cancel it, and then you're surprised that the operation did not run to completion.

  • The Old New Thing

    How do I prevent folders like My Pictures from being recreated?

    • 24 Comments

    Another converse of How do I programmatically create folders like My Pictures if they were manually deleted? and Why do folders like "My Pictures" come back after I delete them? is How do I prevent folders like My Pictures from being recreated?

    Starting in Windows 7, there is a group policy called Disable Known Folders which lets you specify a list of known folders which should be disabled.

    If somebody tries to create a known folder programmatically, the call will fail with ERROR_ACCESS_DISABLED_BY_POLICY.

    Note that this policy only blocks creation of the folder. If the folder already exists, then the policy has no effect. (You're locking the door after the horse has bolted.)

  • The Old New Thing

    Why does my setup program detect the operating system incorrectly the second time I run it?

    • 65 Comments

    A customer reported that when their application called the Get­Version­Ex function, it sometimes reported incorrect values. Specifically, the logs collected from clients shows that the first time the program was run on a Windows 7 machine, the operating system was correctly reported as 6.1.7600 (Windows 7), but the second time it was run, the operating system was erroneously reported as 6.0.6000 (Windows Vista).

    This was definitely strange behavior, and upon further questioning, the customer admitted that their application was a setup program.

    The fact that it was a setup program was the missing ingredient.

    What happened is that the setup program ran, correctly detected the version as Windows 7, and then started installing its pre-requisite components. The installer for one of the pre-requisites failed, causing the entire setup to fail.

    The Program Compatibility Assistant noticed that the initial attempt to install the program failed, and it guessed (based on its internal heuristics) that the problem was that the program had an incorrect operating system version check. After the first setup failed, the Program Compatibility Assistant puts up a dialog box saying, "Hey, I think I know what went wrong. This setup program has a bad operating system version check. Do you want to give it another shot?" If the client says, "Go for it", then it will run the setup program again, but with a false operating system version.

    Unfortunately, the heuristic that the Program Compatibility Assistant used was a false positive in this case, so saying "Go for it" was the wrong answer. (Not like the client had any idea. This was a case of the computer asking the user a question they cannot answer.)

    The fix is to add a manifest to the setup program specifying whether it needs to run as administrator. It doesn't matter what the manifest says as its requirements; the fact that the manifest said anything at all means that the setup program understands the new rules introduced in Windows Vista and doesn't need the Program Compatibility Assistant's help.

    (You can read the Excluding Programs from PCA section for other ways to disable the Program Compatibility Assistant for a program.)

  • The Old New Thing

    The Visual Effects dialog box just tells you what you want to hear

    • 21 Comments

    The Visual Effects dialog box has three options, "Let Windows choose what's best for my computer," "Adjust for best appearance," and "Adjust for crappiest appearance best performance." Some people have discovered the registry key where the Visual Effects dialog box remembers which radio button was most recently checked, but they found that when they programmatically manipulate the registry key, there is no effect on the actual visual settings.

    What's going on?

    What's going on is that the registry key is just there to tell you what you want to hear. It remembers which radio button you clicked, so that when you reopen the dialog box, the same radio button will be selected by default.

    The actual work of changing the setting happens when you click the OK or Apply button. The registry key is just for show.

    If you want to change a Visual Effects setting programmatically, you need to make the corresponding API call for that visual effect. For example, you might call System­Parameters­Info with the SPI_SET­NON­CLIENT­ANIMATION flag to programmatically enable or disable non-client animation.

    Note of course that by doing this you are using a global solution to a local problem. The user's visual effects preferences should be modified by the user, not by a program.

  • The Old New Thing

    How do I hit the Win+PrintScreen hotkey if my tablet doesn't have a PrtSc key?

    • 30 Comments

    Windows 8 added a new hotkey: Win+PrtSc takes a snapshot of your screen and puts it into the Screenshots folder of your Pictures library. But what if you are on a tablet with no PrtSc key?

    On tablets, you can perform the same operation by pressing Windows button + Volume down. Both of these are the hardware buttons on the tablet, not on any keyboard.

  • The Old New Thing

    The case of the mysterious Alternate Data Stream query

    • 12 Comments

    A customer was running Windows Server 2003 ("Still in support until 2015!") and they have some custom application that monitors all disk accesses. They noticed that there were a lot of failed Alternate Data Stream queries coming from Explorer, and that was causing the custom application's logs to fill with largely useless information.

    These Alternate Data Stream queries are being made in order to extract file metadata for the pop-up infotip. (Windows later abandoned the use of Alternate Data Streams for file metadata since Alternate Data Streams were so fragile and were easily damaged or lost.)

    The customer found that if they unchecked Show pop-up description for folder and desktop items, this solved the problem on some of their machines, but not all of them. They asked the Explorer team what else needs to be done to stop the ADS queries.

    The piece they were missing was the status bar. If the status bar is enabled, then it shows the same information that would have appeared in the infotip.

    Turning off the status bar fixed their problem.

  • The Old New Thing

    Why doesn't the New Folder command work in the root of a redirected drive resource in a Remote Desktop session?

    • 27 Comments

    When you connect to another computer via Remote Desktop, you have the option of injecting your local drives into the remote computer, known as Device and Resource Redirection. These injected drives are available under the UNC \\tsclient\X where X is a drive letter on the local machine.

    The name TSCLIENT combines a bunch of internal technical terminology, so it makes perfect sense to the people who wrote it, but not as much to outsiders. (They may have chosen this name just to make themselves look smart.) The letters TS stand for Terminal Services, which was the former name of the technology now known as Remote Desktop. And the word client refers to the local computer, the one that is connected to the remote computer. In Terminal Services terminology, the machine you are connect from is the client, and the machine you are connecting to is the server.

    There's another level of confusion in the name of the feature. People often call these \\tsclient\X thingies Redirected Drives, which collides with the existing name for local drive letters that have been mapped to a network resource. In the user interface, these are usually called Mapped Network Drives. From the command line, you create these things via the NET USE command.

    Okay, enough with the confusing terminology. For today, we're talking about Remote Desktop Device Redirection, where the redirected device is a drive letter.

    If you open My Computer and look under Other, you'll see those drives which were injected from the local computer. Your first tip-off that there's something funny about these drives: They don't show up in the Network Location section like other mapped drives; instead they show up under the rather generic-sounding Other.

    That's because these drives aren't really drives. They are folder shortcuts, a special type of shortcut that grafts one part of the shell namespace into another. The ones created by Remote Desktop Device Redirection are shell instance objects, which is a way of creating certain types of shell extensions using just a handful of registry keys.

    Since they aren't really drives, some things that work for real drives don't work for these fake drives. And one of those things is that Explorer thinks that they don't support the New Folder command because when Explorer asks, "Do you support IStorage?" (because that's the interface that Explorer uses to create new folders), the answer is "No, you silly rabbit. I'm an Other!"

    Now, it turns out that the Terminal Services folks could've customized their Other to say, "Actually, yeah, I do support IStorage." You do this by setting the bit 0x00000008 in the Attributes value of the ShellFolder key when you registered your instance object. The Terminal Services folks forgot to set that bit, and the result is no New Folder button.

    Sorry about that.

    As a workaround, you can create your new folder by typing \\tsclient\X into the address bar. That folder is the thing that the folder shortcut is pointing to (so it's just another name for the same thing), but since it's the real thing, it correctly reports the SFGAO_STORAGE flag, and the New Folder button appears.

  • The Old New Thing

    How do I configure the timeout used by UI0Detect (Interactive Services Detection service)?

    • 10 Comments

    Windows Vista introduced Session 0 Isolation which enforces the rule that services should not display UI. If a service tries to display UI, another service known as the Interactive Services Detection service detects this situation and signals the user that a service wants to display UI and gives the user an opportunity to switch to the service desktop, respond to the UI, and then switch back. If the user ignores the service for about one minute, it switches back automatically, on the assumption that something went bad with the detection and the service is actually finished with its UI. (That way, the user doesn't get stuck staring at session 0 forever.)

    More than one customer wanted to know how to configure this one minute timeout.

    The correct solution to the problem is not to configure Interactive Services Detection but rather to fix your service so it doesn't show UI in session 0.

    It's like saying, "When I mail a letter and get the postal code wrong, the letter reaches the destination eventually, but it takes much longer than a letter sent with the correct postal code. How can I get letters sent with the incorrect postal code to reach their destination faster?"

    The answer is to stop putting the incorrect postal code on your letters.

    In other words, stop throwing garbage on the sidewalk.

    Bonus reading: Troubleshooting Interactive Services Detection.

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