linux-kernel - Re: [PATCH 1/6] seq_file: add seq_read

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Date:   Wed, 11 Nov 2020 08:55:43 +0100
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Christoph Hellwig <hch@....de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] seq_file: add seq_read_iter

On Tue, Nov 10, 2020 at 11:20:28PM +0000, Al Viro wrote:
> On Tue, Nov 10, 2020 at 09:35:11PM +0000, Al Viro wrote:
> > On Tue, Nov 10, 2020 at 09:32:53PM +0000, Al Viro wrote:
> > 
> > > AFAICS, not all callers want that semantics, but I think it's worth
> > > a new primitive.  I'm not saying it should be a prereq for your
> > > series, but either that or an explicit iov_iter_revert() is needed.
> > 
> > Seeing that it already went into mainline, it needs a followup fix.
> > And since it's not -stable fodder (AFAICS), I'd rather go with
> > adding a new primitive...
> 
> Any objections to the following?
> 
> Fix seq_read_iter() behaviour on full pipe
> 
> generic_file_splice_read() will purge what we'd left in pipe in case
> of error; it will *not* do so in case of short write, so we must make
> sure that reported amount of data stored by ->read_iter() matches the
> reality.
> 
> It's not a rare situation (and we already have it open-coded in at least
> one place), so let's introduce a new primitive - copy_to_iter_full().
> Similar to copy_from_iter_full(), it returns true if we had been able
> to copy everything we'd been asked to and false otherwise.  Iterator
> is advanced only on success.
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>

Looks ok to me.