Re: [PATCH v3 3/3] DT: proc: Add runtime overlay interface in /proc

[Grant Likely]

On Fri,  8 Nov 2013 17:06:10 +0200, Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
> Add a runtime interface to /proc to enable generic device tree overlay
> usage.
> 
> Two new /proc files are added:
> 
> /proc/device-tree-overlay & /proc/device-tree-overlay-status
> 
> /proc/device-tree-overlay accepts a stream of a device tree objects and
> applies it to the running kernel's device tree.
> 
> 	$ cat ~/BB-UART2-00A0.dtbo >device-tree-overlay
> 	overlay_proc_release: Applied #2 overlay segments @0
> 
> /proc/device-tree-overlay-status displays the the overlays added using
> the /proc interface
> 
> 	$ cat device-tree-overlay-status
> 	0: 861 bytes BB-UART2:00A0
> 
> The format of the status line is
> 	<ID>: <SIZE> bytes <part-number>:<version>
> 
> <ID> is the id of the overlay
> <SIZE> is the size of the overlay in bytes
> <part-number>, <version> are (optional) root level properties of the DTBO
> 
> You can remove an overlay by echoing the <ID> number of the overlay
> precedded with a '-'
> 
> So
> 	$ echo "-0" >device-tree-overlay-status
> 
> Removes the overlay.
> 
> Note that this seldom works on most platforms since platform_device
> removal is something that almost never works without extra patches.
> 
> Signed-off-by: Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx>

Why /proc? Did you consider using the firmware loading mechanism? While
I expressed concerned about the capebus approach, the loading of
overlays needs to remain under the control of either a driver or the
platform. By default it should not be possible to drop an arbitrary
overlay into /proc/device-tree-overlay and have things change in the
base tree. Along the same lines, I would expect for the device driver or
platform to be able to filter or limit the parts of the tree that are
allowed to be modified.

A side benefit of the firmware loader is that the kernel can obtain the
overlay on its own if needed at boot time without userspace involvement.

g.

> ---
>  fs/proc/proc_devtree.c | 278 +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 278 insertions(+)
> 
> diff --git a/fs/proc/proc_devtree.c b/fs/proc/proc_devtree.c
> index 106a835..48f7925 100644
> --- a/fs/proc/proc_devtree.c
> +++ b/fs/proc/proc_devtree.c
> @@ -16,6 +16,9 @@
>  #include <linux/slab.h>
>  #include <asm/prom.h>
>  #include <asm/uaccess.h>
> +#include <linux/of_fdt.h>
> +#include <linux/idr.h>
> +
>  #include "internal.h"
>  
>  static inline void set_node_proc_entry(struct device_node *np,
> @@ -28,6 +31,275 @@ static inline void set_node_proc_entry(struct device_node *np,
>  
>  static struct proc_dir_entry *proc_device_tree;
>  
> +#if defined(CONFIG_OF_OVERLAY)
> +static struct proc_dir_entry *proc_device_tree_overlay;
> +static struct proc_dir_entry *proc_device_tree_overlay_status;
> +static DEFINE_MUTEX(overlay_lock);
> +static DEFINE_IDR(overlay_idr);
> +
> +struct proc_overlay_data {
> +	void			*buf;
> +	size_t			alloc;
> +	size_t			size;
> +
> +	int 			id;
> +	struct device_node	*overlay;
> +	int			ovinfo_cnt;
> +	struct of_overlay_info	*ovinfo;
> +	unsigned int		failed : 1;
> +	unsigned int		applied : 1;
> +	unsigned int		removing : 1;
> +};
> +
> +static int overlay_proc_open(struct inode *inode, struct file *file)
> +{
> +	struct proc_overlay_data *od;
> +
> +	od = kzalloc(sizeof(*od), GFP_KERNEL);
> +	if (od == NULL)
> +		return -ENOMEM;
> +
> +	od->id = -1;
> +
> +	/* save it */
> +	file->private_data = od;
> +
> +	return 0;
> +}
> +
> +static ssize_t overlay_proc_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
> +{
> +	struct proc_overlay_data *od = file->private_data;
> +	void *new_buf;
> +
> +	/* need to alloc? */
> +	if (od->size + size > od->alloc) {
> +
> +		/* start at 256K at first */
> +		if (od->alloc == 0)
> +			od->alloc = SZ_256K / 2;
> +
> +		/* double buffer */
> +		od->alloc <<= 1;
> +		new_buf = kzalloc(od->alloc, GFP_KERNEL);
> +		if (new_buf == NULL) {
> +			pr_err("%s: failed to grow buffer\n", __func__);
> +			od->failed = 1;
> +			return -ENOMEM;
> +		}
> +
> +		/* copy all we had previously */
> +		memcpy(new_buf, od->buf, od->size);
> +
> +		/* free old buffer and assign new */
> +		kfree(od->buf);
> +		od->buf = new_buf;
> +	}
> +
> +	if (unlikely(copy_from_user(od->buf + od->size, buf, size))) {
> +		pr_err("%s: fault copying from userspace\n", __func__);
> +		return -EFAULT;
> +	}
> +
> +	od->size += size;
> +	*ppos += size;
> +
> +	return size;
> +}
> +
> +static int overlay_proc_release(struct inode *inode, struct file *file)
> +{
> +	struct proc_overlay_data *od = file->private_data;
> +	int id;
> +	int err = 0;
> +
> +	/* perfectly normal when not loading */
> +	if (od == NULL)
> +		return 0;
> +
> +	if (od->failed)
> +		goto out_free;
> +
> +	of_fdt_unflatten_tree(od->buf, &od->overlay);
> +	if (od->overlay == NULL) {
> +		pr_err("%s: failed to unflatten tree\n", __func__);
> +		err = -EINVAL;
> +		goto out_free;
> +	}
> +	pr_debug("%s: unflattened OK\n", __func__);
> +
> +	/* mark it as detached */
> +	of_node_set_flag(od->overlay, OF_DETACHED);
> +
> +	/* perform resolution */
> +	err = of_resolve(od->overlay);
> +	if (err != 0) {
> +		pr_err("%s: Failed to resolve tree\n", __func__);
> +		goto out_free;
> +	}
> +	pr_debug("%s: resolved OK\n", __func__);
> +
> +	/* now build an overlay info array */
> +	err = of_build_overlay_info(od->overlay,
> +			&od->ovinfo_cnt, &od->ovinfo);
> +	if (err != 0) {
> +		pr_err("%s: Failed to build overlay info\n", __func__);
> +		goto out_free;
> +	}
> +
> +	pr_debug("%s: built %d overlay segments\n", __func__,
> +			od->ovinfo_cnt);
> +
> +	err = of_overlay(od->ovinfo_cnt, od->ovinfo);
> +	if (err != 0) {
> +		pr_err("%s: Failed to apply overlay\n", __func__);
> +		goto out_free;
> +	}
> +
> +	od->applied = 1;
> +
> +	mutex_lock(&overlay_lock);
> +	idr_preload(GFP_KERNEL);
> +	id = idr_alloc(&overlay_idr, od, 0, -1, GFP_KERNEL);
> +	idr_preload_end();
> +	mutex_unlock(&overlay_lock);
> +
> +	if (id < 0) {
> +		err = id;
> +		pr_err("%s: failed to get id for overlay\n", __func__);
> +		goto out_free;
> +	}
> +	od->id = id;
> +
> +	pr_info("%s: Applied #%d overlay segments @%d\n", __func__,
> +			od->ovinfo_cnt, od->id);
> +
> +	return 0;
> +
> +out_free:
> +	if (od->id != -1)
> +		idr_remove(&overlay_idr, od->id);
> +	if (od->applied)
> +		of_overlay_revert(od->ovinfo_cnt, od->ovinfo);
> +	if (od->ovinfo)
> +		of_free_overlay_info(od->ovinfo_cnt, od->ovinfo);
> +	/* release memory */
> +	kfree(od->buf);
> +	kfree(od);
> +
> +	return 0;
> +}
> +
> +static const struct file_operations overlay_proc_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= overlay_proc_open,
> +	.write		= overlay_proc_write,
> +	.release	= overlay_proc_release,
> +};
> +
> +/*
> + * Supply data on a read from /proc/device-tree-overlay-status
> + */
> +static int overlay_status_proc_show(struct seq_file *m, void *v)
> +{
> +	int err, id;
> +	struct proc_overlay_data *od;
> +	const char *part_number, *version;
> +
> +	rcu_read_lock();
> +	idr_for_each_entry(&overlay_idr, od, id) {
> +		seq_printf(m, "%d: %d bytes", id, od->size);
> +		/* TODO Make this standardized? */
> +		err = of_property_read_string(od->overlay, "part-number",
> +					&part_number);
> +		if (err != 0)
> +			part_number = NULL;
> +		err = of_property_read_string(od->overlay, "version",
> +					&version);
> +		if (err != 0)
> +			version = NULL;
> +		if (part_number) {
> +			seq_printf(m, " %s", part_number);
> +			if (version)
> +				seq_printf(m, ":%s", version);
> +		}
> +		seq_printf(m, "\n");
> +	}
> +	rcu_read_unlock();
> +
> +	return 0;
> +}
> +
> +static int overlay_status_proc_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, overlay_status_proc_show, __PDE_DATA(inode));
> +}
> +
> +static ssize_t overlay_status_proc_write(struct file *file, const char __user *buf,
> +			     size_t size, loff_t *ppos)
> +{
> +	struct proc_overlay_data *od;
> +	char buffer[PROC_NUMBUF + 1];
> +	char *ptr;
> +	int id, err, count;
> +
> +	memset(buffer, 0, sizeof(buffer));
> +	count = size;
> +	if (count > sizeof(buffer) - 1)
> +		count = sizeof(buffer) - 1;
> +
> +	if (copy_from_user(buffer, buf, count)) {
> +		err = -EFAULT;
> +		goto out;
> +	}
> +
> +	ptr = buffer;
> +	if (*ptr != '-') {	/* only removal supported */
> +		err = -EINVAL;
> +		goto out;
> +	}
> +	ptr++;
> +	err = kstrtoint(strstrip(ptr), 0, &id);
> +	if (err)
> +		goto out;
> +
> +	/* find it */
> +	mutex_lock(&overlay_lock);
> +	od = idr_find(&overlay_idr, id);
> +	if (od == NULL) {
> +		mutex_unlock(&overlay_lock);
> +		err = -EINVAL;
> +		goto out;
> +	}
> +	/* remove it */
> +	idr_remove(&overlay_idr, id);
> +	mutex_unlock(&overlay_lock);
> +
> +	err = of_overlay_revert(od->ovinfo_cnt, od->ovinfo);
> +	if (err != 0) {
> +		pr_err("%s: of_overlay_revert failed\n", __func__);
> +		goto out;
> +	}
> +	/* release memory */
> +	of_free_overlay_info(od->ovinfo_cnt, od->ovinfo);
> +	kfree(od->buf);
> +	kfree(od);
> +
> +	pr_info("%s: Removed overlay with id %d\n", __func__, id);
> +out:
> +	return err < 0 ? err : count;
> +}
> +
> +static const struct file_operations overlay_status_proc_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= overlay_status_proc_open,
> +	.read		= seq_read,
> +	.write		= overlay_status_proc_write,
> +	.llseek		= seq_lseek,
> +	.release	= single_release,
> +};
> +#endif
> +
>  /*
>   * Supply data on a read from /proc/device-tree/node/property.
>   */
> @@ -239,5 +511,11 @@ void __init proc_device_tree_init(void)
>  		return;
>  	}
>  	proc_device_tree_add_node(root, proc_device_tree);
> +#if defined(CONFIG_OF_OVERLAY)
> +	proc_device_tree_overlay = proc_create_data("device-tree-overlay",
> +			       S_IWUSR, NULL, &overlay_proc_fops, NULL);
> +	proc_device_tree_overlay_status = proc_create_data("device-tree-overlay-status",
> +			       S_IRUSR| S_IWUSR, NULL, &overlay_status_proc_fops, NULL);
> +#endif
>  	of_node_put(root);
>  }
> -- 
> 1.7.12
> 

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