Controlling delete on close state

Dor2003ger · August 5, 2024, 2:12pm

Hey, looking at the FastFat source it seems like the CreateFile -> FILE_DELETE_ON_CLOSE_FLAG is a CBB flag , promoted to FCB_STATE_DELETE_ON_CLOSE on cleanup.

We can modify FCB_STATE_DELETE_ON_CLOSE through a set info with file disposition information deleteFile=true , as mentioned in the archives .

I was thinking it wouldn’t be possible to clear the delete on close flag (specified at create) , but now, looking at the file disposition information ex structure I’m not so sure - FILE_DISPOSITION_ON_CLOSE allows that?

Dor2003ger · August 5, 2024, 3:03pm

Reviewing the delete sample I can see it can indeed be unset, but another question regarding the sample : they set / unset the delete on close flag in the stream context based on set info requests they see, wouldn’t then the StreamContext->DeleteOnClose flag reflect the true delete on close state of the file? I’m aware of racing deletes , but they will check on post cleanup if the file was deleted regardless if there were racing deletes or not and I’m not sure why

rod_widdowson · August 5, 2024, 3:17pm

Does the comment above about oplocks help?

Dor2003ger · August 5, 2024, 6:15pm

Hmm excuse my ignorance , what comment ?

rod_widdowson · August 6, 2024, 10:11am

Hmm excuse my ignorance , what comment ?

This one.

github.com

microsoft/Windows-driver-samples/blob/b3af8c8f9bd508f54075da2f2516b31d05cd52c8/filesys/fastfat/cleanup.c#L283


      
          AcquiredFcb = TRUE;
          
          //
          //  Do a check here if this was a DELETE_ON_CLOSE FileObject, and
          //  set the Fcb flag appropriately.
          //
          
          if (FlagOn(Ccb->Flags, CCB_FLAG_DELETE_ON_CLOSE)) {
          
              NT_ASSERT( NodeType(Fcb) != FAT_NTC_ROOT_DCB );
          
              //
              //  Transfer the delete-on-close state to the FCB.  We do this rather
              //  than leave the CCB_FLAG_DELETE_ON_CLOSE flag set so that if we
              //  end up breaking an oplock and come in again we won't try to break
              //  the oplock again (and again, and again...).
              //
          
              SetFlag( Fcb->FcbState, FCB_STATE_DELETE_ON_CLOSE );
              ClearFlag( Ccb->Flags, CCB_FLAG_DELETE_ON_CLOSE );

TBH it has been a while since I walked the delete path in FAT and the whole "undo delete on close" thing has been added since. But I do know to be wary of the ways of oplocks for they are subtle and quick to anger

system · September 5, 2024, 10:11am

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