Date: Sun, 22 Feb 2004 18:22:09 +0000
From: Christoph Hellwig <hch@infradead.org>
To: Ram Pai <linuxram@us.ibm.com>
Cc: Steve Lord <lord@xfs.org>, Dean Roehrich <roehrich@clink.americas.sgi.com>,
        linux-xfs@oss.sgi.com
Subject: Re: DMAPI test suite.
Message-ID: <20040222182209.A642@infradead.org>
References: <200402181519.i1IFJS9i11055016@clink.americas.sgi.com> <1077265286.7503.37.camel@dyn319009bld.beaverton.ibm.com> <40360FC8.4060405@xfs.org> <1077473812.2822.32.camel@localhost.localdomain>
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In-Reply-To: <1077473812.2822.32.camel@localhost.localdomain>; from linuxram@us.ibm.com on Sun, Feb 22, 2004 at 10:16:52AM -0800
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On Sun, Feb 22, 2004 at 10:16:52AM -0800, Ram Pai wrote:
> Looking through the xfs dmapi code, 2 questions pop up:
> 1. How can the pre_unmount event, when generated through the put_super()
> code provide the DM_UNMOUNT_FORCE information.  There is now way for the
> put_super() code to know if the unmount is a forceful one or not. 

It can't.

> 2. And finally I find that all the DMAPI event generators are stubbed
> to   fs_nosys or fs_noerr or fs_noval . So does XFS ever generate DM
> events ?

You need to load the xfs_dmapi module to get an implementation.  It's
in the CVS repository at oss.sgi.com.

> > Al Viro is distinctly anti dmapi, so chances are slim to none I would
> > say.
> 
> hmm...that makes it difficult. Is he against Dmapi implemented in VFS or
> against the overall idea of supporting DMAPI anywhere in linux?  I hope
> he is just against DMAPI implemented at the VFS level and is ok with 
> supporting filesystems to implement it. 

DMAPI is an extremly broken specification, it fits hardly into an unix
enviroment and not into Linux at all.  SGI tries to provide a best-fit
dmapi implementation anyways, but it's just not something that should
go into an mainline kernel.

If you want to see HSM support in a kernel.org kernel start by designing
a saner specification than dmapi.