linux-kernel - Re: [PATCH -next 1/3] seq: Add a seq

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Message-ID: <1386804701.2479.2.camel@joe-AO722>
Date:	Wed, 11 Dec 2013 15:31:41 -0800
From:	Joe Perches <joe@...ches.com>
To:	Ryan Mallon <rmallon@...il.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Kees Cook <keescook@...omium.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next 1/3] seq: Add a seq_overflow test.

On Thu, 2013-12-12 at 10:27 +1100, Ryan Mallon wrote:
> On 11/12/13 16:12, Joe Perches wrote:
> > seq_printf and seq_puts returns are often misused.
> > 
> > Instead of checking the seq_printf or seq_puts return,
> > add a new seq_overflow function to test if a seq_file has
> > overflowed the available buffer space.
> > 
> > This will eventually allow seq_printf and seq_puts to be
> > converted to have a void return instead of the int return
> > that is often assumed to have a size_t value instead of an
> > error/no-error value.
> > 
> > Signed-off-by: Joe Perches <joe@...ches.com>
> > ---
> >  fs/seq_file.c            | 15 ++++++++-------
> >  include/linux/seq_file.h |  2 ++
> >  2 files changed, 10 insertions(+), 7 deletions(-)
> > 
> > diff --git a/fs/seq_file.c b/fs/seq_file.c
> > index 1d641bb..aab0736 100644
> > --- a/fs/seq_file.c
> > +++ b/fs/seq_file.c
> > @@ -14,16 +14,17 @@
> >  #include <asm/uaccess.h>
> >  #include <asm/page.h>
> >  
> > -
> > -/*
> > - * seq_files have a buffer which can may overflow. When this happens a larger
> > - * buffer is reallocated and all the data will be printed again.
> > - * The overflow state is true when m->count == m->size.
> > +/**
> > + * seq_overflow - test if a seq_file has overflowed the space available
> > + * @m: the seq_file handle
> > + *
> > + * Returns -1 when an overflow has occurred, 0 otherwise.
> >   */
> > -static bool seq_overflow(struct seq_file *m)
> > +int seq_overflow(struct seq_file *m)
> >  {
> > -	return m->count == m->size;
> > +	return m->count == m->size ? -1 : 0;
> >  }
> > +EXPORT_SYMBOL(seq_overflow);
> 
> What is the reasoning in making this return int instead of bool? Having
> it return int encourages people to do:
> 
> 	return seq_overflow(s);
> 
> When used in seq_file functions will return -EPERM (-1) to user-space,
> which is confusing. It should probably return bool and let the caller
> sort out the correct error to return.

It was intended to make the return from seq_printf the same.

Anyway, the patch series is out of date (see Al's comments).
I'll update it later unless you or someone else does it first.


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