Re: [Bug-tar] bug in 'file has changed as we read it'

[Paul Eggert]

On 09/13/10 10:35, Michal Svoboda wrote:
> Paul Eggert wrote:
>> There are applications where it's important that the metadata be
>> consistent with the data: for example, it could be that the data
>> contain time stamps, which should always predate the ctime, and
>> if the tar image contains data with timestamps after the ctime,
>> then the tar image is inconsistent.
> 
> How can this happen without modifying the data?

My scenario was assuming that some other process modified the data.
But that is a scenario of concern.  User processes can set the mtime
after modifying the data (this is normal, for applications such as
cp -p) so tar cannot trust the mtime here.  In contrast, ctime is
more trustable: in most environments user processes can't set the
ctime to arbitrary values.  That is why tar should use ctime here.