linux-kernel - Re: [PATCH v2] coredump: Use vmsplice_to_pipe() for pipes in dump_emit

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Message-ID: <20221130034059.GA2246@bytedance>
Date:   Tue, 29 Nov 2022 19:40:59 -0800
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Peilin Ye <peilin.ye@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] coredump: Use vmsplice_to_pipe() for pipes in
 dump_emit_page()

On Sat, Nov 19, 2022 at 04:46:17AM +0000, Al Viro wrote:
> On Mon, Oct 31, 2022 at 02:03:49PM -0700, Peilin Ye wrote:
> 
> > +	n = vmsplice_to_pipe(file, &iter, 0);
> > +	if (n == -EBADF)
> > +		n = __kernel_write_iter(cprm->file, &iter, &pos);
> 
> Yuck.  If anything, I would rather put a flag into coredump_params
> and check it instead; this check for -EBADF is both unidiomatic and
> brittle.  Suppose someday somebody looks at vmsplice(2) and
> decides that it would make sense to lift the "is it a pipe" check
> into e.g. vmsplice_type().  There's no obvious reasons not to,
> unless one happens to know that coredump relies upon that check done
> in vmsplice_to_pipe().  It's asking for trouble several years down
> the road.
> 
> Make it explicit and independent from details of error checking
> in vmsplice(2).

Thanks for the review!  I was a bit hesitant about introducing a new
field to coredump_params for this optimization.  Will do it in v3.

Peilin Ye