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Date: Wed, 17 Jul 2002 09:49:40 -0700
From: Andrew Morton <akpm@zip.com.au>
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To: Anton Altaparmakov <aia21@cantab.net>
CC: Linus Torvalds <torvalds@transmeta.com>,
       lkml <linux-kernel@vger.kernel.org>
Subject: Re: [patch 13/13] lseek speedup
References: <3D3598F0.FBBA9DB6@zip.com.au> <5.1.0.14.2.20020717171311.00b00380@pop.cus.cam.ac.uk>
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Anton Altaparmakov wrote:
> 
> >  Now, why are we taking i_sem for lseek/readdir
> >exclusion and not a per-file lock?
> 
> Because it also excludes against directory modifications, etc. Just imagine
> what "rm somefile" or "mv somefile otherfile" or "touch newfile" would do
> to the directory contents and what a concurrent readdir() would do... A
> very loud *BANG* is the only thing that springs to mind...

That's different.  i_size, contents of things, yes - i_sem for
those.

But protection of struct file should not be via any per-inode thing.

> btw. the directory modification locking rules are written up in
> Documentation/filesystems/directory-locking by our very own VFS maintainer
> Al Viro himself... (-;

Doesn't cover lseek...

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