Commit 86b54881 authored by Mike Tipton's avatar Mike Tipton Committed by Georgi Djakov
Browse files

debugfs: Add write support to debugfs_create_str() 

Currently, debugfs_create_str() only supports reading strings from
debugfs. Add support for writing them as well.

Based on original implementation by Peter Zijlstra [0]. Write support
was present in the initial patch version, but dropped in v2 due to lack
of users. We have a user now, so reintroduce it.

[0] https://lore.kernel.org/all/YF3Hv5zXb%2F6lauzs@hirez.programming.kicks-ass.net/



Signed-off-by: default avatarMike Tipton <quic_mdtipton@quicinc.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230807142914.12480-2-quic_mdtipton@quicinc.com


Signed-off-by: default avatarGeorgi Djakov <djakov@kernel.org>
parent 2ccdd1b1

fs/debugfs/file.c

+46 −2
Original line number Diff line number Diff line
@@ -904,8 +904,52 @@ EXPORT_SYMBOL_GPL(debugfs_create_str); 
static ssize_t debugfs_write_file_str(struct file *file, const char __user *user_buf,

				      size_t count, loff_t *ppos)

{

	/* This is really only for read-only strings */

	return -EINVAL;

	struct dentry *dentry = F_DENTRY(file);

	char *old, *new = NULL;

	int pos = *ppos;

	int r;



	r = debugfs_file_get(dentry);

	if (unlikely(r))

		return r;



	old = *(char **)file->private_data;



	/* only allow strict concatenation */

	r = -EINVAL;

	if (pos && pos != strlen(old))

		goto error;



	r = -E2BIG;

	if (pos + count + 1 > PAGE_SIZE)

		goto error;



	r = -ENOMEM;

	new = kmalloc(pos + count + 1, GFP_KERNEL);

	if (!new)

		goto error;



	if (pos)

		memcpy(new, old, pos);



	r = -EFAULT;

	if (copy_from_user(new + pos, user_buf, count))

		goto error;



	new[pos + count] = '\0';

	strim(new);



	rcu_assign_pointer(*(char **)file->private_data, new);

	synchronize_rcu();

	kfree(old);



	debugfs_file_put(dentry);

	return count;



error:

	kfree(new);

	debugfs_file_put(dentry);

	return r;

}



static const struct file_operations fops_str = {