linux-kernel - Re: [PATCH] cxl/port: Constify 'struct bin

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Message-ID: <4b3560e7-68f2-480d-8337-2699c999e55c@t-8ch.de>
Date: Wed, 15 Jan 2025 09:44:46 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Alison Schofield <alison.schofield@...el.com>
Cc: Davidlohr Bueso <dave@...olabs.net>, 
	Jonathan Cameron <jonathan.cameron@...wei.com>, Dave Jiang <dave.jiang@...el.com>, 
	Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>, 
	Dan Williams <dan.j.williams@...el.com>, linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cxl/port: Constify 'struct bin_attribute'

On 2025-01-14 15:01:22-0800, Alison Schofield wrote:
> On Tue, Jan 14, 2025 at 10:25:14PM +0100, Thomas Weißschuh wrote:
> > The sysfs core now allows instances of 'struct bin_attribute' to be
> > moved into read-only memory. Make use of that to protect them against
> > accidental or malicious modifications.
> > 
> > Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> > ---
> >  drivers/cxl/port.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/cxl/port.c b/drivers/cxl/port.c
> > index 4c83f6a22e584f1f248807c7fa4fe932d6f11d67..664fde6ff53862c6aef2a83be56c1518b6bfbadd 100644
> > --- a/drivers/cxl/port.c
> > +++ b/drivers/cxl/port.c
> > @@ -153,7 +153,7 @@ static int cxl_port_probe(struct device *dev)
> >  }
> >  
> >  static ssize_t CDAT_read(struct file *filp, struct kobject *kobj,
> > -			 struct bin_attribute *bin_attr, char *buf,
> > +			 const struct bin_attribute *bin_attr, char *buf,
> >  			 loff_t offset, size_t count)
> >  {
> >  	struct device *dev = kobj_to_dev(kobj);
> > @@ -170,7 +170,7 @@ static ssize_t CDAT_read(struct file *filp, struct kobject *kobj,
> >  				       port->cdat.length);
> >  }
> >  
> > -static BIN_ATTR_ADMIN_RO(CDAT, 0);
> > +static const BIN_ATTR_ADMIN_RO(CDAT, 0);
> >  
> >  static umode_t cxl_port_bin_attr_is_visible(struct kobject *kobj,
> >  					    const struct bin_attribute *attr, int i)
> > @@ -184,13 +184,13 @@ static umode_t cxl_port_bin_attr_is_visible(struct kobject *kobj,
> >  	return 0;
> >  }
> >  
> > -static struct bin_attribute *cxl_cdat_bin_attributes[] = {
> > +static const struct bin_attribute *const cxl_cdat_bin_attributes[] = {
> >  	&bin_attr_CDAT,
> >  	NULL,
> >  };
> >  
> > -static struct attribute_group cxl_cdat_attribute_group = {
> > -	.bin_attrs = cxl_cdat_bin_attributes,
> > +static const struct attribute_group cxl_cdat_attribute_group = {
> > +	.bin_attrs_new = cxl_cdat_bin_attributes,
> >  	.is_bin_visible = cxl_port_bin_attr_is_visible,
> >  };
> 
> What's the point of s/bin_attrs/bin_attrs_new above?

The new type of cxl_cdat_bin_attributes is not compatible with
.bin_attrs. Therefore .bin_attrs_new was introduced.
When all users have been migrated to the new type, .bin_attrs itself will
be switched to the new type and all users moved back to bin_attr.
In one big centrally managed commit to avoid annoying subsystem
maintainers (even more).

The same issue exists in .read_new/.write_new but in this specific case
that is handled transparently in BIN_ATTR_ADMIN_RO().

> 
> --Alison
> 
> >  
> > 
> > ---
> > base-commit: 7f5b6a8ec18e3add4c74682f60b90c31bdf849f2
> > change-id: 20250114-sysfs-const-bin_attr-cxl-d102eab47586
> > 
> > Best regards,
> > -- 
> > Thomas Weißschuh <linux@...ssschuh.net>
> >