Sorry for absence, I had absolutely no time last month.

1. In general multitask OS guaranteer that single file operation is atomic
not sequence of them. So claims that OS must provide this contract are
incorrect. Want we or not but file system is a shared resource and it is
necessary to process correctly file access errors due to locks.

2. I wrote my point in my very first post. AV scanners behavior is
predictable: they locks a file for a short period of time and then release
it. So several retries is enough to understand: is this FS failure and the
file is lost or is this only temporary lock by AV and processing can continue.