On Jul. 22, 2010, 20:24 +0300, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, Jul 22, 2010 at 10:03 AM, Jan Engelhardt <jengelh@xxxxxxxxxx> wrote: >> >> I beg to differ. ctime is not completely useless. It reflects changes on >> the inode for when you don't you change the content. > > Uh. Yes. Except that why is file metadata really different from file > data? Most people really don't care. And a lot of people have asked > for creation dates - and I seriously doubt that Windows people > complain a lot about the fact that there you have mtime for metadata > changes too. > > The point being that Unix ctime semantics certainly have well-defined > semantics, but they are in no way "better" than having a real creation > time, and are often worse. Yeah, having create time would be important. That said, having a non user-settable modify timestamp is crucial for quickly determining whether a file has changed. Benny > > Just imagine what you could do as an MIS person if you actually had a > creation time you could somewhat trust? You talk about seeing somebody > change the permissions of /etc/passwd, but realistically, absent > preexisting semantics, who would really ask for that? The only reason > you mention that as an example of what you can do with ctime is that > that is indeed pretty much the _only_ thing you can do with ctime, and > it really isn't that useful. > > In contrast, with a creation date, you see the difference between > people overwriting files by writing to them, or overwriting files by > creating a new one and moving it over the old one. At a guess, that > would be quite as useful to a sysadmin as ctime is now (my gut feel is > that it would be more so, but whatever). > > IOW, there really isn't anything magically good about UNIX ctime > semantics, and in fact they are totally broken in the presence of > extended attributes (that's file data, but it only changes ctime? WTF > is up with that? Yes, I know why it happens, and it makes sense within > the insane unix ctime rules, but no way does it make sense in a bigger > picture unless you are in total denial and try to claim that xattrs > are just metadata despite having contents). > > And yes, I am also sure that there are applications that do depend on > ctime semantics. Trond mentioned NFS serving, and that's unfortunate. > I bet there are others. That's inevitable when you have 40 years of > history. So I'm not claiming that re-using ctime is painfree, but for > somebody that cares about samba a lot, I bet it's a _lot_ better than > adding a new time that almost nobody actually supports as things stand > now. > > Of people can just use xattrs and do it all entirely in user space. I > assume that's what samba does now, even outside of birthtime. > > Linus > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
