Re: fgetattr/fsetattr file operation

[Brian Molnar <brian.molnar@gmail.com>]

> On Thu, Jun 4, 2009 at 12:04 PM, Andreas Dilger <adilger@sun.com> wrote:
> This sounds very strange - different processes (or even the same
> process using different file handles) will see different results
> for fstat() which are yet different from stat().  I can't imagine
> that applications would like this at all.

Ya, no doubt a good deal of applications would get very confused if
they didn't know the difference. And it is not the goal of this FS to
support the use of general applications.

But, because a process has a 'private copy' of the file when it opens
it for write-mode (this being an intended feature of this
file-system), it's imperative that the application be given the
ability to access the data and metadata of the private copy as well as
the on-disk version. The on-disk file's metadata would be retrieved
via a path-based stat(2) (or by opening another instance of the file
read-only and fstat'ing the fd), and the private copy's metadata would
be retrieved via fstat(2).

> Maybe you should go back and explain why this behaviour is useful,
> before we burden the kernel with it.

Hardly a burden. It's an interface addition that is completely
optional to each filesystem. In Miklos' patch, if the fgetattr method
is not set in the file_operations struct, then the behavior is to
fallback to the original getattr function.


Cheers,
- Brian
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