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From:   David Howells <dhowells@redhat.com>
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To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     dhowells@redhat.com, Miklos Szeredi <miklos@szeredi.hu>,
        Karel Zak <kzak@redhat.com>, Ian Kent <raven@themaw.net>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        Steven Whitehouse <swhiteho@redhat.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Jann Horn <jannh@google.com>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Linux API <linux-api@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 00/17] VFS: Filesystem information and notifications [ver #17]
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Date:   Tue, 03 Mar 2020 14:19:58 +0000
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Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:

> +	fd = do_sys_open(dfd, filename, flags, 0000);
> +	if (fd <= 0)
> +		return fd;
> +
> +	retval = ksys_read(fd, buffer, bufsize);
> +
> +	__close_fd(current->files, fd);

If you can use dentry_open() and vfs_read(), you might be able to avoid
dealing with file descriptors entirely.  That might make it worth a syscall.

You're going to be asked for writefile() you know ;-)

David