Re: [RFC] atomic create+open

[Miklos Szeredi]

> > Say you have NFS mount on /mnt and a bind mount over the regular file
> > /mnt/foo.  You do open("/mnt/foo", O_RDWR | O_CREAT, 0644).  How do
> > you solve the atomic open case.
> 
> > If you open in ->lookup("foo") you will be opening the wrong file,
> > unless you want to follow mounts inside ->lookup.
> 
> Firstly, if that is the case, then you will have dentries for both the
> covered and the covering copies of /mnt/foo. A simple test of
> have_submounts() on the dentry will suffice to tell the filesystem.
> whether or not it should open the file.

And if the bind is umounted after NFS determined not to open the file,
and at the same time it changes to a symlink on the server (not very
likely I agree, but possible nonetheless), then shit happens.

> Secondly, Linux doesn't actually allow bind mounts on top of regular
> files.

It does.  Try it.

Miklos

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