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

[Pantelis Antoniou]

Hi Rob,

> On Apr 15, 2015, at 04:27 , Rob Herring <robherring2@xxxxxxxxx> wrote:
> 
> On Tue, Apr 7, 2015 at 2:23 PM, Pantelis Antoniou
> <pantelis.antoniou@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
>> ---
>> 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.
> 

Itâs 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 thatâs 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 thatâs 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

â Pantelis

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