linux-ext4 - Re: Extended file stat: Splitting file- and fs-specific info?

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Date:	Fri, 11 May 2012 02:54:13 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Roland McGrath <roland@...k.frob.com>
Cc:	David Howells <dhowells@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	"bfields@...ldses.org Fields" <bfields@...ldses.org>,
	"smfrench@...il.com French" <smfrench@...il.com>,
	"ben@...adent.org.uk Hutchings" <ben@...adent.org.uk>,
	"Trond.Myklebust@...app.com Myklebust" <Trond.Myklebust@...app.com>,
	"linux-fsdevel@...r.kernel.org Devel" <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 List" <linux-ext4@...r.kernel.org>,
	linux-api@...r.kernel.org, libc-alpha@...rceware.org
Subject: Re: Extended file stat: Splitting file- and fs-specific info?

On 2012-05-10, at 11:10 AM, Roland McGrath wrote:
> POSIX specifies st_blksize thusly: "A file system-specific preferred
> I/O block size for this object. In some file system types, this may
> vary from file to file."
> 
> Since there is only one available to POSIX applications, it should map
> to the one that's described as "preferred IO size for general usage".

Sure, but statxat() isn't a POSIX API.

While I agree with the idea that there should be enough information about the underlying layout for applications to be able to submit good IO, it doesn't help if we have a bunch of extra fields that have vague meanings. 

They will get filled in by the filesystem in a haphazard way, and will not be used by application developers that don't understand what they mean.

Cheers, Andreas





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