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

Pantelis Antoniou
2015-04-23T12:00:14Z

Hi Rob,

> On Apr 15, 2015, at 04:27 , Rob Herring <robherring2@gmail.com> wrote:
>
> On Tue, Apr 7, 2015 at 2:23 PM, Pantelis Antoniou
> <pantelis.antoniou@konsulko.com> wrote:
>> 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.
>
> This one should be a separate patch.
>

OK.

>> * A per overlay targets sysfs attribute listing the targets of
>> the installed overlay.
>
> What are targets? "targets lists targets" does not help me. The
> documentation doesn't help me either.
>

It lists the targets of the overlay that has been applied. What do
you need in order to be helped? I mean what do you want listed?

>> * 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);
>
> Why are you using bin attribute? You are complicating the
> implementation needlessly.
>

It’s the same reason that the device tree core is using it.

Believe it or not, this is the simplest way to do it.
If you take a look at the sysfs attribute implementation, the binary
implementation is the one that’s using the least amount of code.

To use a non-binary method we have to register per ktype sysfs_ops
and duplicate the way the non-binary attribute works.

For the gory details look at sysfs_add_file_mode_ns() in fs/sysfs/file.c

I can add the sysfs_ops but that’s going to be more complicated not less.

>> +
>> +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;
>
> Leaking memory here and holding the mutex.
>

OK

>> + memcpy(s, name, len);
>> + s += len;
>> + *s++ = '\n';
>> + }
>> + if (s + 1 >= e)
>> + return -ENOMEM;

> And here.
>

OK

>> + *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);
>
> Same question about bin attr here.
>

Same answer as above.

>> +
>> /**
>> * 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

Regards

— Pantelis