[PATCH v2 3/4] of: overlay: Add sysfs attributes

Pantelis Antoniou
2015-04-07T19:24:12Z

Implement a number of sysfs attributes for overlays.

* A throw once master enable switch to protect against any
further overlay applications if the administrator desires so.

* A per overlay targets sysfs attribute listing the targets of
the installed overlay.

* A per overlay can_remove sysfs attribute that reports whether
the overlay can be removed or not due to another overlapping overlay.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
---
drivers/of/overlay.c | 167 ++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 166 insertions(+), 1 deletion(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index f17f5ef..c54d097 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -21,6 +21,7 @@
#include <linux/err.h>
#include <linux/idr.h>
#include <linux/sysfs.h>
+#include <linux/atomic.h>

#include "of_private.h"

@@ -55,8 +56,12 @@ struct of_overlay {
struct kobject kobj;
};

+/* master enable switch; once set to 0 can't be re-enabled */
+static atomic_t ov_enable = ATOMIC_INIT(1);
+
static int of_overlay_apply_one(struct of_overlay *ov,
struct device_node *target, const struct device_node *overlay);
+static int overlay_removal_is_ok(struct of_overlay *ov);

static int of_overlay_apply_single_property(struct of_overlay *ov,
struct device_node *target, struct property *prop)
@@ -345,6 +350,144 @@ static struct kobj_type of_overlay_ktype = {

static struct kset *ov_kset;

+static ssize_t enable_read(struct file *filp, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf,
+ loff_t offset, size_t count)
+{
+ char tbuf[3];
+
+ if (offset < 0)
+ return -EINVAL;
+
+ if (offset >= sizeof(tbuf))
+ return 0;
+
+ if (count > sizeof(tbuf) - offset)
+ count = sizeof(tbuf) - offset;
+
+ /* fill in temp */
+ tbuf[0] = '0' + atomic_read(&ov_enable);
+ tbuf[1] = '\n';
+ tbuf[2] = '\0';
+
+ /* copy to buffer */
+ memcpy(buf, tbuf + offset, count);
+
+ return count;
+}
+
+static ssize_t enable_write(struct file *filp, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf,
+ loff_t off, size_t count)
+{
+ unsigned int new_enable;
+
+ if (off != 0 || (buf[0] != '0' && buf[0] != '1'))
+ return -EINVAL;
+
+ new_enable = (unsigned int)(buf[0] - '0');
+ if (new_enable > 1)
+ return -EINVAL;
+
+ /* NOP for same value */
+ if (new_enable == atomic_read(&ov_enable))
+ return count;
+
+ /* if we've disabled it, no going back */
+ if (atomic_read(&ov_enable) == 0)
+ return -EPERM;
+
+ atomic_set(&ov_enable, new_enable);
+ return count;
+}
+
+/* just a single char + '\n' + '\0' */
+static BIN_ATTR_RW(enable, 3);
+
+static ssize_t targets_read(struct file *filp, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf,
+ loff_t offset, size_t count)
+{
+ struct of_overlay *ov = kobj_to_overlay(kobj);
+ struct of_overlay_info *ovinfo;
+ char *tmpbuf, *s, *e;
+ const char *name;
+ ssize_t ret;
+ int i, len;
+
+ /* allocate work buffer; we know that PAGE_SIZE is enough */
+ tmpbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+ if (tmpbuf == NULL)
+ return -ENOMEM;
+
+ s = tmpbuf;
+ e = tmpbuf + PAGE_SIZE;
+
+ mutex_lock(&of_mutex);
+
+ /* targets */
+ for (i = 0; i < ov->count; i++) {
+ ovinfo = &ov->ovinfo_tab[i];
+
+ name = of_node_full_name(ovinfo->target);
+ len = strlen(name);
+ if (s + len + 1 >= e)
+ return -ENOMEM;
+ memcpy(s, name, len);
+ s += len;
+ *s++ = '\n';
+ }
+ if (s + 1 >= e)
+ return -ENOMEM;
+ *s++ = '\0';
+
+ /* the buffer is zero terminated */
+ len = s - tmpbuf;
+
+ mutex_unlock(&of_mutex);
+
+ /* perform the read */
+ ret = memory_read_from_buffer(buf, count, &offset, tmpbuf, len);
+
+ /* free the temporary buffer */
+ kfree(tmpbuf);
+
+ return ret;
+}
+
+/* targets property */
+static BIN_ATTR_RO(targets, PAGE_SIZE);
+
+static ssize_t can_remove_read(struct file *filp, struct kobject *kobj,
+ struct bin_attribute *bin_attr, char *buf,
+ loff_t offset, size_t count)
+{
+ struct of_overlay *ov = kobj_to_overlay(kobj);
+ char tbuf[3];
+
+ if (offset < 0)
+ return -EINVAL;
+
+ if (offset >= sizeof(tbuf))
+ return 0;
+
+ if (count > sizeof(tbuf) - offset)
+ count = sizeof(tbuf) - offset;
+
+ /* fill in temp */
+ tbuf[0] = '0' + overlay_removal_is_ok(ov);
+ tbuf[1] = '\n';
+ tbuf[2] = '\0';
+
+ /* copy to buffer */
+ memcpy(buf, tbuf + offset, count);
+
+ return count;
+}
+
+/* can_remove property */
+static BIN_ATTR_RO(can_remove, 3);
+
/**
* of_overlay_create() - Create and apply an overlay
* @tree: Device node containing all the overlays
@@ -360,6 +503,10 @@ int of_overlay_create(struct device_node *tree)
struct of_overlay *ov;
int err, id;

+ /* administratively disabled */
+ if (!atomic_read(&ov_enable))
+ return -EPERM;
+
/* allocate the overlay structure */
ov = kzalloc(sizeof(*ov), GFP_KERNEL);
if (ov == NULL)
@@ -416,6 +563,22 @@ int of_overlay_create(struct device_node *tree)
goto err_cancel_overlay;
}

+ /* create targets file */
+ err = sysfs_create_bin_file(&ov->kobj, &bin_attr_targets);
+ if (err != 0) {
+ pr_err("%s: sysfs_create_bin_file() failed for tree@%s\n",
+ __func__, tree->full_name);
+ goto err_cancel_overlay;
+ }
+
+ /* create can_remove file */
+ err = sysfs_create_bin_file(&ov->kobj, &bin_attr_can_remove);
+ if (err != 0) {
+ pr_err("%s: sysfs_create_bin_file() failed for tree@%s\n",
+ __func__, tree->full_name);
+ goto err_cancel_overlay;
+ }
+
/* add to the tail of the overlay list */
list_add_tail(&ov->node, &ov_list);

@@ -596,5 +759,7 @@ int of_overlay_init(void)
if (!ov_kset)
return -ENOMEM;

- return 0;
+ rc = sysfs_create_bin_file(&ov_kset->kobj, &bin_attr_enable);
+ WARN(rc, "%s: error adding enable attribute\n", __func__);
+ return rc;
}
--
1.7.12