linux-ext4 - Re: [PATCH 1/6] xstat: Add a pair of system calls to make extended file stats available

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Message-ID: <18195.1335447156@redhat.com>
Date:	Thu, 26 Apr 2012 14:32:36 +0100
From:	David Howells <dhowells@...hat.com>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	dhowells@...hat.com, linux-fsdevel@...r.kernel.org,
	linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
	samba-technical@...ts.samba.org, linux-ext4@...r.kernel.org,
	wine-devel@...ehq.org, kfm-devel@....org, nautilus-list@...me.org,
	linux-api@...r.kernel.org, libc-alpha@...rceware.org
Subject: Re: [PATCH 1/6] xstat: Add a pair of system calls to make extended file stats available

Andreas Dilger <adilger@...ger.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
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