linux-kernel - Re: [PATCH] fw_cfg: use __ATTR_RO

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Date:   Wed, 27 Feb 2019 08:51:11 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     qemu-devel@...gnu.org, linux-kernel@...r.kernel.org, somlo@....edu
Subject: Re: [PATCH] fw_cfg: use __ATTR_RO_MODE to define rev sysfs

On Wed, Feb 27, 2019 at 01:33:19PM +0800, Wei Yang wrote:
> On Tue, Feb 26, 2019 at 11:10:06AM -0500, Michael S. Tsirkin wrote:
> >On Tue, Feb 26, 2019 at 03:31:59PM +0800, Wei Yang wrote:
> >> Leverage __ATTR_RO_MODE to define rev sysfs instead of using open code
> >> to define the attribute.
> >> 
> >> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
> >> ---
> >>  drivers/firmware/qemu_fw_cfg.c | 13 ++++---------
> >>  1 file changed, 4 insertions(+), 9 deletions(-)
> >> 
> >> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> >> index 039e0f91dba8..a1293cbd7adb 100644
> >> --- a/drivers/firmware/qemu_fw_cfg.c
> >> +++ b/drivers/firmware/qemu_fw_cfg.c
> >> @@ -296,18 +296,13 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev)
> >>  	return 0;
> >>  }
> >>  
> >> -static ssize_t fw_cfg_showrev(struct kobject *k, struct attribute *a, char *buf)
> >> +static ssize_t fw_cfg_rev_show(struct kobject *k, struct kobj_attribute *a,
> >> +			       char *buf)
> >>  {
> >>  	return sprintf(buf, "%u\n", fw_cfg_rev);
> >>  }
> >> -
> >> -static const struct {
> >> -	struct attribute attr;
> >> -	ssize_t (*show)(struct kobject *k, struct attribute *a, char *buf);
> >> -} fw_cfg_rev_attr = {
> >> -	.attr = { .name = "rev", .mode = S_IRUSR },
> >> -	.show = fw_cfg_showrev,
> >> -};
> >> +static const struct kobj_attribute fw_cfg_rev_attr =
> >> +	__ATTR_RO_MODE(fw_cfg_rev, 0400);
> >>  
> >>  /* fw_cfg_sysfs_entry type */
> >>  struct fw_cfg_sysfs_entry {
> >
> >
> >Looks like this will change the name from "rev" to "fw_cfg_rev".
> >That's a userspace visible change which we should not do lightly.
> 
> You are right, I should keep the interface untouched.
> 
> To keep it user un-visible, we could change like below:
> 
> -       __ATTR_RO(fw_cfg_rev);
> +       __ATTR_RO(rev);
> 
> Is this better for you?


Also why use 0400 and not S_IRUSR?

> >> -- 
> >> 2.19.1
> 
> -- 
> Wei Yang
> Help you, Help me