On 7.08.23 17:29, Mike Tipton wrote:
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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Hi Greg,
Looks like the original code was reviewed two years ago (not sure if it
counts). But in any case, i need an ack from you to apply this.
There is no build dependency with the rest of the patches (but there is a
functional one). It should be also fine if you apply it directly, if you
prefer so?
Thanks,
Georgi
Signed-off-by: Mike Tipton <quic_mdtipton@xxxxxxxxxxx>
---
fs/debugfs/file.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 46 insertions(+), 2 deletions(-)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index b7711888dd17..87b3753aa4b1 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -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 = {
