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Message-ID: <15768.40630.512787.879557@charged.uio.no>
Date: Mon, 30 Sep 2002 20:57:58 +0200
To: Matthew Wilcox <willy@debian.org>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>,
       Marcelo Tosatti <marcelo@conectiva.com.br>,
       Chuck Lever <cel@netapp.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>,
       Linux FSdevel <linux-fsdevel@vger.kernel.org>,
       NFS maillist <nfs@lists.sourceforge.net>
Subject: Re: [PATCH] 2.4.20 Direct IO patch for NFS. (Note: a trivial API change...)
In-Reply-To: <20020930195235.P18377@parcelfarce.linux.theplanet.co.uk>
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	<20020930195235.P18377@parcelfarce.linux.theplanet.co.uk>
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From: Trond Myklebust <trond.myklebust@fys.uio.no>
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>>>>> " " == Matthew Wilcox <willy@debian.org> writes:

    >> -static int blkdev_direct_IO(int rw, struct inode * inode,
    >> struct kiobuf * iobuf, unsigned long blocknr, int blocksize)
    >> +static int blkdev_direct_IO(int rw, struct file * filp, struct
    >> kiobuf * iobuf, unsigned long blocknr, int blocksize) {
    >> + struct inode * inode =
    >>  	filp->f_dentry->d_inode->i_mapping->host;
    >> return generic_direct_IO(rw, inode, iobuf, blocknr, blocksize,
    >> blkdev_get_block); }
    >>

     > isn't that two dereferences more than necessary for a local
     > filesystem?

IIRC this is an issue with block filesystems: the i_mapping->host may
differ from d_inode.

It is in any case just the exact same dereference that is being made
in the current version of generic_file_direct_IO(). The API change
simply moves this dereference down into the filesystem code.

Cheers,
  Trond
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