[cvsnt] Re: NAV vs. CVSNT

[Ori Berger]

BHarriger wrote:
 > We were recently bit by the NAV/CVSNT incompatibility
 > (wasn't aware of it until last week) so I'm now trying
 > to work out the problem with Symantec.

At least in some versions of NAV in the past, deleting a file would 
  not actually delete it immediately, but rather a few milliseconds 
later.

Internally, to delete a file on NT, one has to do the following:
1. Open the file with Delete permission
2. Mark the file 'pending deletion'
3. Close the file

Upon the last close of the file (it can be open multiple times....), 
  the filesystem is supposed to make the file disappear, but I have 
  not seen any official statement anywhere that ensures that this 
will  be atomic or within a well known time frame.

Many file system filters (NAV is one, FUNDELETE from SysInternals is 
another) delay the actual deletion of the file because they either 
mark it 'not pending deletion' before close and then do some work 
before deletion, or otherwise maintain another open handle to the 
same file.

I don't know which API is used in CVSNT, but unlink(), remove() and 
whatever the Win32 API for this is, all map to the three items above 
in NT's Native API. The end result is that, although all phases of 
the deletion are successful, the file is _still_ there for some time 
(a few milliseconds to a few seconds!) after it was expected to 
disappear. And this can lead to many subtle bugs.

I'm not 100% sure, but I think rename is guaranteed to be atomic (in 
the sense that a successful return from the rename call indicates 
that the filename has already changed on the filesystem, rather than 
that it will be renamed at some point in the future). If this is 
indeed so, then renaming the file into oblivion before deleting it 
(e.g., rename it to something like 'random-name-10897.deleteme' 
before deleting), will solve the conflict.

Disclaimer: I solved the CVSNT/NAV conflict by disabling NAV 
altogether, but I have traced problems in other software in the past 
to being a result of the files not disappearing immediately when 
deleted. This is only a speculation.