linux-kernel - Re: [PATCH 04/25] vfs: add i_op->atomic

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Date:	Tue, 13 Mar 2012 16:11:35 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"Myklebust\, Trond" <Trond.Myklebust@...app.com>
Cc:	"viro\@ZenIV.linux.org.uk" <viro@...IV.linux.org.uk>,
	"linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"hch\@infradead.org" <hch@...radead.org>,
	"sfrench\@samba.org" <sfrench@...ba.org>,
	"sage\@newdream.net" <sage@...dream.net>,
	"ericvh\@gmail.com" <ericvh@...il.com>
Subject: Re: [PATCH 04/25] vfs: add i_op->atomic_open()

"Myklebust, Trond" <Trond.Myklebust@...app.com> writes:

> On Wed, 2012-03-07 at 22:22 +0100, Miklos Szeredi wrote:
>> +
>> +	if ((nd->flags & LOOKUP_OPEN) && dir_inode->i_op->atomic_open) {
>> +		struct file *filp;
>> +
>> +		filp = atomic_open(nd, dentry, op, want_write, &create_error);
>> +		if (filp) {
>> +			dput(dentry);
>> +			return filp;
>> +		}
>> +		/* fall back to plain lookup */
>> +	}
>
> Would it be possible to allow the filesystem to return a new dentry even
> if it can't complete the actual open? That way we can return the actual
> symlink that caused the open to fail instead of looking it up separately
> (which may be subject to races).

This should be possible, but I'm reluctant to add more arguments to
->atomic_open.  Other possibilites that come to mind:

  return -ELOOKEDUP - caller should retry d_lookup and proceed with the result

  call opendata_set_dentry(od, dentry) and return NULL - caller checks
  opendata for non-NULL dentry and proceeds with that

Thanks,
Miklos
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