Re: [PATCH 1/6] xstat: Add a pair of system calls to make extended file stats available

[David Howells <dhowells@redhat.com>]

Andreas Dilger <adilger@dilger.ca> wrote:

> > The idea was initially proposed as a set of xattrs that could be
> > retrieved with getxattr(), but the general preferance proved to be
> > for new syscalls with an extended stat structure.
> 
> I would comment that it was the opposite.  It was originally a
> stat()-like extension that degraded into a messy getxattr() mess.

Ummm...  No, my first attempt was definitely through getxattr().  You even
commented on it.

> > The fields in struct xstat come in a number of classes:
> > 
> > (0) st_dev, st_blksize, st_information.
> > 
> >     These are local data and are always available.
> 
> For the extra two bits it would cost us, I don't think st_blksize
> and st_information should always be returned.

Fair enough.

> st_blksize may be variable for a distributed filesystem,

I wonder if there's a way to make this explicit - or is it something that if
the bit isn't set, you can't use the value in st_blksize.  I wonder if this
value always has to be non-zero to make sure existing stat() doesn't explode.

> and some of the fields in st_information (offline) may not be free to access
> either.

True.

David