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How volsnap driver know this write operation should be copy-on-write or not?

Sooncheol_WonSooncheol_Won Member Posts: 21
edited October 2019 in NTDEV

I'm studying Volume Shadow Copy Service.

In Windows Internals Part 2,

Volsnap avoids copy-on-write operations for the paging file, hibernation file, and the difference data stored in the System Volume Information folder. All other files will get copy-on-write protection.

Volsnap driver is upper volume filter driver so I think it cannot figure out this writing block(sector) is from what filename or what file attributes has but it maybe can.

How can volsnap know that information?

And how does volsnap know which logical block is not used and how does volsnap redirect to where writing operations? (to another block? or to temporary file?)

Comments

  • Sooncheol_WonSooncheol_Won Member Posts: 21

    I found some variable in IRP structure.

    irp->Tail->Overlay->OriginalFileObject

    This looks like contains original file object which has filename, attributes and Vpb...
    Does volsnap uses these and redirect to some other backup file?

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