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Re: Why do Virus Scanners hate Subversion

From: Ryan Schmidt <subversion-2006q2_at_ryandesign.com>
Date: 2006-05-03 12:20:48 CEST

On May 2, 2006, at 19:31, Jesse Hogan wrote:

> svn: In directory 'Databases/eMax/StoredProcs'
> svn: Can't move source to dest
> svn: Can't move 'Databases/eMax/StoredProcs/_svn/tmp/props/
> dbo.spConfigWriteStartingConfiguration.PRC.svn-work' to 'Databases/
> eMax/StoredProcs/_svn/props/
> dbo.spConfigWriteStartingConfiguration.PRC.svn-work': Permission
> denied

> I've done a little research on these types of error messages and
> the only explanation I've found is that a virus scanner is
> tampering with the newly downloaded files. This seems to be what I
> am seeing because I can disable the virus scanner to get the
> checkout to work. Am I right in blaming virus scanners for these
> types of error message. Also, what exactly is happening. Is the
> virus scanner placing a lock on these files which causes svn to
> abend. Can anything be done to make svn more tolerant of virus
> scanners. I hope so because this is one of the first things a user
> sees when (s)he begins using svn which, I have witness, leads to
> bad impressions.

Possibly, the user should instead get a bad impression of an
operating system that's plagued by viruses, and entertain the
possibility of switching to one that is not.


I believe the situation arises because the virus scanner is
constantly on the lookout for new files being added to the system,
and, when it finds them, scans them for possible threats. To scan the
file, the scanner must open the file, read its contents and then
close it. But Subversion's mode of operation is to rapidly create
files in its tmp directory, then immediately move them elsewhere, as
in the error message you copied above: Subversion created the file in
the tmp/props directory and now wanted to move it to the props
directory, but was denied. Presumably, right after Subversion created
the file, the virus scanner noticed its existence and opened it and
started reading it, but had not yet finished reading it by the time
Subversion wanted to move it. As far as I know, on Windows, you
cannot move a file that is open (and as far as I know, that's not a
problem on Unix-like operating systems). Presumably, in the cases
where it works properly, the virus scanner is either quick enough
that it can read the entire file by the time Subversion tries to move
it, or slow enough that it never notices the file in its original
location in the tmp directory and only catches it later after it's
been successfully moved.

A workaround that Subversion could possibly employ would be to try
several times to move a file if it fails on the first attempt,
waiting a fraction of a second between attempts, and to only error
out if several consecutive attempts have failed.

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Received on Wed May 3 12:21:55 2006

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