linux-kernel - Re: [PATCH 1/2] fs: add SEEK_HOLE and SEEK

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Message-ID: <20110422045054.GB17795@infradead.org>
Date:	Fri, 22 Apr 2011 00:50:54 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Josef Bacik <josef@...icpanda.com>
Cc:	Eric Blake <eblake@...hat.com>, linux-kernel@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/2] fs: add SEEK_HOLE and SEEK_DATA flags

[Eric: please don't drop the Cc list, thanks!]

On Thu, Apr 21, 2011 at 09:22:55PM -0400, Josef Bacik wrote:
> > since all files have a virtual hole at the end, but leaves the position
> > unchanged). ??I'd have to write a test program on Solaris to see whether that
> > definition is actually true, or if it is a bug in the Solaris man page.
> >
> 
> lseek's purpose is to reposition the file position, so I'd imagine
> this is just a bug in the man page.

I would be surprised if the bug is around for such a long time, but
otherwise I concur.

> Except you can have blocks allocated past i_size, so returning i_size
> isn't necessarily correct.  Obviously the idea is to have most of the
> filesystems doing the correct thing, but for my first go around I just
> was going to do one since I expect quite a bit of repainting for this
> bikeshed is yet to be done.  But I guess if you have data past i_size
> doing this would encourage the various fs people to fix it.

Trying to be smart about our semantics is not helpful here.  The
interface has been out in Solaris for a while, and we'll have to either
stick to it or use different names for the interface.  And staying
compatible is far more useful for userspace programmers.

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