ENT-11988: Atomic copy_from in files promise

[larsewi]

Changes to files promise in copy_from attribute:

• The new file (i.e., <FILENAME>.cfnew) is now created with correct
  permission during remote copy. Previously it would be created with
  default permissions.
• The destination file (i.e., <FILENAME>) is no longer deleted on
  backup during file copy. Previously it would be renamed to
  <FILENAME>.cfsaved, causing the original file to dissappear. Now an
  actual copy of the original file with the same permissions is created
  instead.

As a result, there will no longer be a brief moment where the original
file is inaccessible.

Back-ported to:

• ENT-11988: Atomic copy_from in files promise (3.24.x) #5613
• ENT-11988: Atomic copy_from in files promise (3.21.x) #5614

[larsewi]

@cf-bottom Jenkins please :)

[cf-bottom]

Sure, I triggered a build:

Jenkins: https://ci.cfengine.com/job/pr-pipeline/11253/

Packages: http://buildcache.cfengine.com/packages/testing-pr/jenkins-pr-pipeline-11253/

[vpodzime]

Looks good to me except that we should use (the code from) CopyRegularFileDisk(), I believe.

[larsewi]

Looks good to me except that we should use (the code from) CopyRegularFileDisk(), I believe.

Thanks 🍻

[craigcomstock]

Yeah, makes sense. I had to go looking for the "move cfnew to dest" code and found it at

        if (rename(changes_new, changes_dest) == 0)
        {
            RecordChange(ctx, pp, attr, "Moved '%s' to '%s'", new, dest);
            *result = PromiseResultUpdate(*result, PROMISE_RESULT_CHANGE);
        }

Interesting that the RecordChange() call uses different variables than the rename() call but they "should" be the same. ;)

[vpodzime]

ACK