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

[Ian Turner]

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

Maybe. But the Linux implementors were just trying to grab the libc interface, 
which doesn't say anything about fpathconf().

Right now you can check if the kernel supports O_NOATIME at all using fcntl(); 
If you set the flag at open() (or using F_SETFL), then if the kernel supports 
it, the flag will still be there when you use F_GETFL. Otherwise, the flag 
will remain unset.

HOWEVER, right now even the linux kernel itself does not know which 
filesystems support this feature. We are working on adding this 
functionality, but it may take some time to get it accepted, as the original 
patch was itself contraversial.

Probably the interface to find out if O_NOATIME works will be simple: If you 
do open(), and O_NOATIME is not OK for this filesystem, then open() will just 
return EINVAL. I'm OK with adding an fpathconf() facility too, but the big 
work is going to be just teaching the kernel which filesystems work and which 
don't.

--Ian