You are kidding, right? dup3() is not for general use?
> That's a big difference.
Look, I'm not really bent on a particular mechanism of actually making sure that programmers have a reliable interface for doing this. Using fsync() before close() is the only portable solution now, but it is far from optimal. I think there is very little doubt about that. And we all know it sucks to high heaven on ext3 in ordered mode.
I don't know what the best way is: new call, some kind of flag to open that says O_ALWAYSDATABEFOREMETADATA, rename2(), close_with_magic() or whatever. But, saying that application programmers cannot grok this kind of stuff is just not true. They can and they will, only if given the tools. Just like they did dup3() and friends (and as you point out, there is little danger of misuse - these are new calls).
As I said many times before, overloading current pattern with non-portable behaviour is dangerous, because it provides false sense of robustness and ties one up to a particular FS and kernel. If we can get POSIX updated so that rename() actually means "always data before metadata, but don't put on disk now", then it may even fly. But, I don't know how that's going to make guarantees retroactively, when even Linux features file systems that don't do that (e.g. ext3 in writeback mode).
Also, having things like delayed allocation, where metadata can legitimately be committed before data, is really useful. Most short lived temporary files will never see disk platters, therefore making things faster and disks last longer. Meaning, keeping the old cruft around ain't that bad.
As for utility programs that are called from scripts, you can use dd with conv=fsync or conv=fdatasync in your pipe to commit files to disk today. On FreeBSD, they already have standalone fsync program for that. Yeah, I know. It sucks. But, your usual tools don't have to make any decisions on fsync()-ing - you can.
Copyright © 2018, Eklektix, Inc.
Comments and public postings are copyrighted by their creators.
Linux is a registered trademark of Linus Torvalds