linux-kernel - Re: [PATCH 09/14] fs: don't change the address limit for ->write_iter in __kernel

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Message-ID: <20200518064246.GA19296@lst.de>
Date:   Mon, 18 May 2020 08:42:46 +0200
From:   Christoph Hellwig <hch@....de>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Christoph Hellwig <hch@....de>, Al Viro <viro@...iv.linux.org.uk>,
        Ian Kent <raven@...maw.net>,
        David Howells <dhowells@...hat.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        netfilter-devel@...r.kernel.org
Subject: Re: [PATCH 09/14] fs: don't change the address limit for
 ->write_iter in __kernel_write

On Sat, May 16, 2020 at 11:04:36AM +0800, Hillf Danton wrote:
> > +	if (file->f_op->write_iter) {
> > +		struct kvec iov = { .iov_base = (void *)buf, .iov_len = count };
> > +		struct kiocb kiocb;
> > +		struct iov_iter iter;
> > +
> > +		init_sync_kiocb(&kiocb, file);
> > +		kiocb.ki_pos = *pos;
> > +		iov_iter_kvec(&iter, WRITE, &iov, 1, count);
> > +		ret = file->f_op->write_iter(&kiocb, &iter);
> > +		if (ret > 0)
> > +			*pos = kiocb.ki_pos;
> > +	} else if (file->f_op->write) {
> > +		mm_segment_t old_fs = get_fs();
> > +
> > +		set_fs(KERNEL_DS);
> 
> Would you please shed light on who need it if a workqueue worker does
> not, given the access to buf? 

Can you rephrase the question, I unfortunately do not understand it at
all as-is.