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\$Extend\$MYLOG 
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Joined: Fri Aug 12, 2016 00:23
Posts: 4
Post \$Extend\$MYLOG
I'm looking at an NTFS volume where a file called "\$Extend\$MYLOG" exists. I don't fully know the history of this volume, but it is causing mount issues on Windows. I'd like to ask this community if anybody knows what this file might be. Is this possibly a file that NTFS-3g may have created for its own use? Alternatively, does NTFS-3g allow users to create files under \$Extend? Any information would be appreciated. I cannot look at NTFS-3g source code.

- Craig (MSFT)


Fri Aug 12, 2016 01:32
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NTFS-3G Lead Developer

Joined: Tue Sep 04, 2007 17:22
Posts: 1286
Post Re: \$Extend\$MYLOG
Hi,

Quote:
Is this possibly a file that NTFS-3g may have created for its own use?

No. Files specific to ntfs-3g are put into \.NTFS-3G
Quote:
Alternatively, does NTFS-3g allow users to create files under \$Extend?

No. Through ntfs-3g you cannot write directly to any file/directory whose number is less than 16 (metadata files) and \$Extend is number 11.

Regards

Jean-Pierre


Fri Aug 12, 2016 08:19
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Joined: Fri Aug 12, 2016 00:23
Posts: 4
Post Re: \$Extend\$MYLOG
Thank you Jean-Pierre.

A follow-up if I may. These will probably sound silly. Does NTFS-3g in any way try to prevent \$Extend from becoming non-resident? If \$Extend happens to be non-resident, does NTFS-3g work fine with it?


Thu Aug 18, 2016 06:47
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NTFS-3G Lead Developer

Joined: Tue Sep 04, 2007 17:22
Posts: 1286
Post Re: \$Extend\$MYLOG
Hi,

Quote:
Does NTFS-3g in any way try to prevent \$Extend from becoming non-resident?

No. Becoming non-resident is controlled by $AttrDef which only considers attribute types, and $Extend has standard attribute types.

This leads me to mention that files and directories can be inserted into $Extend through several ways (plain create, mknod, hard linking, symbolic linking). These are not expected to interfere with metadata, and I do not feel they should be prevented, or maybe names whose first character is a "$" should be considered reserved. What is your view about it ?

Quote:
If \$Extend happens to be non-resident, does NTFS-3g work fine with it?

Yes.

Regards

Jean-Pierre


Thu Aug 18, 2016 09:34
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Joined: Fri Aug 12, 2016 00:23
Posts: 4
Post Re: \$Extend\$MYLOG
jpa wrote:
Quote:
Does NTFS-3g in any way try to prevent \$Extend from becoming non-resident?

No. Becoming non-resident is controlled by $AttrDef which only considers attribute types, and $Extend has standard attribute types.

Entirely reasonable, and what I expected. Only reason I ask is because on Windows for a long time there has been an explicit check to prevent \$Extend from becoming non-resident. This is because of a compatibility issue with Windows XP. Windows XP and earlier will fail to mount a volume where \$Extend in non-resident. Vista and later are fine.

jpa wrote:
This leads me to mention that files and directories can be inserted into $Extend through several ways (plain create, mknod, hard linking, symbolic linking). These are not expected to interfere with metadata, and I do not feel they should be prevented, or maybe names whose first character is a "$" should be considered reserved. What is your view about it ?

Doesn't this contradict your earlier answer when I asked if users could create files under \$Extend? I took the earlier answer to mean that users could not create files under \$Extend.

My view is that \$Extend and everything underneath it (recursively) is for private use by the file system itself, and users (or even kernel components, excepting the file system itself) should not be allowed to modify anything under there, including creating new files. On Windows we protect everything under \$Extend fiercely. The mere presence of that extra file \$Extend\$MYLOG that I asked about earlier is in fact causing a group of users to not be able to mount their volumes on the Anniversary Update.

Also, going back to your first reply, you mention you protect system files with numbers less than 16. I would hope that you also protect files under \$Extend, such as (but not limited to) $ObjId, $Quota, $Reparse, $RmMetadata, and $UsnJrnl. These files don't have well-known file numbers, certainly >= 16, but they are still file system metadata files. Similarly files under \$Extend\$RmMetadata and so on.


Thu Aug 18, 2016 21:53
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