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debugfs: Add write support to debugfs_create_str()

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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: Mike Tipton <quic_mdtipton@quicinc.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230807142914.12480-2-quic_mdtipton@quicinc.com
Signed-off-by: Georgi Djakov <djakov@kernel.org>
This commit is contained in:
Mike Tipton 2023-08-07 07:29:12 -07:00 committed by Georgi Djakov
parent 2ccdd1b13c
commit 86b5488121
1 changed files with 46 additions and 2 deletions
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48
fs/debugfs/file.c
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@ -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 = {