adding attributes in sysfs for block devices

[Ed L Cashin <ecashin@xxxxxxxxxx>]

Hi.  In sysfs there are already default attributes provided by the
block layer (see drivers/block/genhd.c and fs/partitions/check.c).

  root@makki root# cat /sys/block/etherd\!e6.0/size 
  781422768

Those are sectors.  Anyway, I can add more attributes, like this
"state" attribute, which is either "up", "up,closewait", "down", or
"down,closewait".

  root@makki root# cat /sys/block/etherd\!e6.0/state 
  up

I'm adding the attribute as shown below, but it means using a struct
disk_attribute that is defined in genhd.c, which seems strange, since
if this is the right way, I'd expect that struct to be in a header
file.

What is The Right Way to add attributes in sysfs to block devices?

#include <linux/genhd.h>
#include "aoe.h"

/* add attributes for our block devices in sysfs
 */
struct disk_attribute { /* shouldn't this be in a kernel header? */
	struct attribute attr;
	ssize_t (*show)(struct gendisk *, char *);
};

static ssize_t aoedisk_show_state(struct gendisk * disk, char *page)
{
	struct aoedev *d = disk->private_data;

	return snprintf(page, PAGE_SIZE,
			"%s%s\n",
			(d->flags & DEVFL_UP) ? "up" : "down",
			(d->flags & DEVFL_CLOSEWAIT) ? ",closewait" : "");
}

static struct disk_attribute disk_attr_state = {
	.attr = {.name = "state", .mode = S_IRUGO },
	.show = aoedisk_show_state
};

/* called after add_disk */
static void
aoeblk_add_sysfs(struct aoedev *d)
{
	/* create all the sysfs files (just one now) */
	sysfs_create_file(&d->gd->kobj, &disk_attr_state.attr);
}

/* called before del_gendisk */
void
aoeblk_rm_sysfs(struct aoedev *d)
{
	/* remove all the sysfs files (just one now) */
	sysfs_remove_link(&d->gd->kobj, "state");
}


-- 
  Ed L Cashin <ecashin@xxxxxxxxxx>


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