linux-kernel - RE: [PATCH v3 04/10] fs/ntfs3: Add file operations and implementation

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Date:   Fri, 4 Sep 2020 12:49:35 +0000
From:   Konstantin Komarov <almaz.alexandrovich@...agon-software.com>
To:     Al Viro <viro@...iv.linux.org.uk>
CC:     "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pali@...nel.org" <pali@...nel.org>,
        "dsterba@...e.cz" <dsterba@...e.cz>,
        "aaptel@...e.com" <aaptel@...e.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "joe@...ches.com" <joe@...ches.com>,
        "mark@...mstone.com" <mark@...mstone.com>
Subject: RE: [PATCH v3 04/10] fs/ntfs3: Add file operations and implementation

From: Al Viro <viro@....linux.org.uk> On Behalf Of Al Viro
Sent: Friday, August 28, 2020 6:56 PM
> On Fri, Aug 28, 2020 at 07:39:32AM -0700, Konstantin Komarov wrote:
> 
> > +static int ntfs_atomic_open(struct inode *dir, struct dentry *dentry,
> > +			    struct file *file, u32 flags, umode_t mode)
> > +{
[]
> > +		if (d_really_is_positive(dentry)) {
> > +			if (file->f_mode & FMODE_OPENED) {
> 
> 	How do we get FMODE_OPENED here?
> 
> > +				dput(d);
> > +				err = 0;
> > +			} else
> > +				err = finish_no_open(file, d);
> > +			goto out1;
> > +		}
> > +		WARN_ON(d);
> > +	}
> > +
> > +	if (!(flags & O_CREAT)) {
> > +		err = -ENOENT;
> > +		goto out1;
> > +	}
> 
> 	Just return finish_no_open() in that case.  And let the caller handle
> that.
> 
> > +	err = ntfs_create_inode(dir, dentry, file, mode, 0, NULL, 0, excl, fnd,
> > +				&inode);
> > +
> > +out1:
> > +	fnd_put(fnd);
> > +out:
> > +	ni_unlock(ni);
> > +
> > +	return err;
> > +}
> 
> BTW, what's the point of that ni_lock() here?  d_in_lookup() is stable
> regardless of that and any attempts to create something in the parent
> are serialized by ->i_rwsem.  If you want it around the actual file
> creation, why not take it just there, and replace the open-coded
> ntfs_lookup() with the call of the real thing?  As in
> 	if (d_in_lookup(dentry)) {
> 		d = ntfs_lookup(....);
> 		if (IS_ERR(d))
> 			return d;
> 		if (d)
> 			dentry = d;
> 	}
>         if (!(flags & O_CREAT) || d_really_is_positive(dentry))
> 		return finish_no_open(file, d);
> 	/* deal with creation of file */
> 	ni_lock(...);
> 	....

Thanks for the feedback! We refactored the atomic_open() based on
your concerns. Will be published in v4 patch today.