Re: [Bug-tar] Re: [patch] O_NOATIME support

[Joerg Schilling]

Ian Turner <address@hidden> wrote:

> Paul,
>
> It's a fine heuristic. I'm still concerned that we read a small file on NFS 
> at 
> the beginning of the archive, which happens to be in cache, and decide at 
> that point that O_NOATIME works for the entire filesystem, when actually, it 
> doesn't. I don't see any way around this, other than second-guessing yourself 
> all the time.
>
> Another, possibly more reliable way of detecting this, would just be to do 
> statfs(), and see if the filesystem type is one known to not work. Then you 
> (probably) don't have to worry about false negatives; the only way O_NOATIME 
> won't work in that case is if the kernel doesn't support it, so the only bad 
> behavior allowed by the heuristic is to call utimes() on possibly several 
> files at the beginning of the archive, until it finds one that isn't being 
> accessed, at which time it would switch to O_NOATIME.
>
> Another approach might just be to ask the kernel (via uname()) if it supports 
> O_NOATIME -- that is, if it is at least version 2.6.8. If that's too much of 
> a hack, a sysctl could be addde to ask this question to a future kernel, so 
> that we would only nede to use uname() for, say, kernels 2.6.8 - 2.6.14.

Should't a clean Linux implementation offer a related [f]pathconf() call for 
this feature?

Jörg

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