linux-kernel - Re: [PATCH -v2] lib/notifier-error-inject: fix error when writing errno to debugfs file

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Message-ID: <93c044ca-7d2f-e23f-8eb4-72c133737a15@redhat.com>
Date:   Mon, 19 Sep 2022 11:20:13 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Akinobu Mita <akinobu.mita@...il.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, corbet@....net, osalvador@...e.de,
        shuah@...nel.org, Zhao Gongyi <zhaogongyi@...wei.com>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        Yicong Yang <yangyicong@...ilicon.com>
Subject: Re: [PATCH -v2] lib/notifier-error-inject: fix error when writing
 errno to debugfs file

On 17.09.22 09:14, Akinobu Mita wrote:
> The simple attribute files do not accept a negative value since the
> commit 488dac0c9237 ("libfs: fix error cast of negative value in
> simple_attr_write()"), so we can no longer use DEFINE_SIMPLE_ATTRIBUTE() to
> define a file operations for errno value.
> 
> Fixes: 488dac0c9237 ("libfs: fix error cast of negative value in simple_attr_write()")
> Reported-by: Zhao Gongyi <zhaogongyi@...wei.com>
> Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>

But shouldn't we fix simple_attr_write() instead?

I mean, simple_attr_read() might use attr->fmt to print a signed value, 
but simple_attr_write() fails on signed values now?

I might be wrong, but there is a disconnect. I feel like 
simple_attr_write() should similarly make decisions based on attr->fmt.

> ---
> v2: Fix Reported-by line
> 
>   lib/notifier-error-inject.c | 38 ++++++++++++++++++++++++++++++-------
>   1 file changed, 31 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/notifier-error-inject.c b/lib/notifier-error-inject.c
> index 21016b32d313..30ec41f58d53 100644
> --- a/lib/notifier-error-inject.c
> +++ b/lib/notifier-error-inject.c
> @@ -3,20 +3,44 @@
>   
>   #include "notifier-error-inject.h"
>   
> -static int debugfs_errno_set(void *data, u64 val)
> +static int notifier_err_errno_show(struct seq_file *m, void *data)
>   {
> -	*(int *)data = clamp_t(int, val, -MAX_ERRNO, 0);
> +	int *value = m->private;
> +
> +	seq_printf(m, "%d\n", *value);
> +
>   	return 0;
>   }
>   
> -static int debugfs_errno_get(void *data, u64 *val)
> +static int notifier_err_errno_open(struct inode *inode, struct file *file)
>   {
> -	*val = *(int *)data;
> -	return 0;
> +	return single_open(file, notifier_err_errno_show, inode->i_private);
> +}
> +
> +static ssize_t notifier_err_errno_write(struct file *file, const char __user *ubuf, size_t len,
> +					loff_t *offp)
> +{
> +	struct seq_file *m = file->private_data;
> +	int *value = m->private;
> +	int ret;
> +
> +	ret = kstrtoint_from_user(ubuf, len, 0, value);
> +	if (ret)
> +		return ret;
> +
> +	*value = clamp(*value, -MAX_ERRNO, 0);
> +
> +	return len;
>   }
>   
> -DEFINE_SIMPLE_ATTRIBUTE(fops_errno, debugfs_errno_get, debugfs_errno_set,
> -			"%lld\n");
> +static const struct file_operations fops_errno = {
> +	.owner = THIS_MODULE,
> +	.open = notifier_err_errno_open,
> +	.read = seq_read,
> +	.write = notifier_err_errno_write,
> +	.llseek = seq_lseek,
> +	.release = single_release,
> +};
>   
>   static struct dentry *debugfs_create_errno(const char *name, umode_t mode,
>   				struct dentry *parent, int *value)

-- 
Thanks,

David / dhildenb