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Date:   Fri, 28 Aug 2020 16:55:31 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Konstantin Komarov <almaz.alexandrovich@...agon-software.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        pali@...nel.org, dsterba@...e.cz, aaptel@...e.com,
        willy@...radead.org, rdunlap@...radead.org, joe@...ches.com,
        mark@...mstone.com
Subject: Re: [PATCH v3 04/10] fs/ntfs3: Add file operations and implementation

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)
> +{
> +	int err;
> +	bool excl = !!(flags & O_EXCL);
> +	struct inode *inode;
> +	struct ntfs_fnd *fnd = NULL;
> +	struct ntfs_inode *ni = ntfs_i(dir);
> +
> +	ni_lock(ni);
> +
> +	if (d_in_lookup(dentry)) {
> +		struct dentry *d;
> +
> +		fnd = fnd_get(&ntfs_i(dir)->dir);
> +		if (!fnd) {
> +			err = -ENOMEM;
> +			goto out;
> +		}
> +
> +		d = __ntfs_lookup(dir, dentry, fnd);
> +		if (IS_ERR(d)) {
> +			err = PTR_ERR(d);
> +			d = NULL;
> +			goto out1;
> +		}
> +
> +		if (d)
> +			dentry = d;
> +
> +		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(...);
	....

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