Date: Sat, 9 Dec 2023 16:09:40 -0800
From: Paul M Stillwell Jr <paul.m.stillwell.jr@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Tony Nguyen <anthony.l.nguyen@...el.com>, <davem@...emloft.net>,
	<pabeni@...hat.com>, <edumazet@...gle.com>, <netdev@...r.kernel.org>,
	<jacob.e.keller@...el.com>, <vaishnavi.tipireddy@...el.com>,
	<horms@...nel.org>, <leon@...nel.org>, Pucha Himasekhar Reddy
	<himasekharx.reddy.pucha@...el.com>
Subject: Re: [PATCH net-next v5 2/5] ice: configure FW logging

On 12/7/2023 6:19 PM, Jakub Kicinski wrote:
> On Thu, 7 Dec 2023 16:28:27 -0800 Paul M Stillwell Jr wrote:
>> On 12/6/2023 7:53 PM, Jakub Kicinski wrote:
>>> On Tue,  5 Dec 2023 13:12:45 -0800 Tony Nguyen wrote:
>>>> +/**
>>>> + * ice_debugfs_parse_cmd_line - Parse the command line that was passed in
>>>> + * @src: pointer to a buffer holding the command line
>>>> + * @len: size of the buffer in bytes
>>>> + * @argv: pointer to store the command line items
>>>> + * @argc: pointer to store the number of command line items
>>>> + */
>>>> +static ssize_t ice_debugfs_parse_cmd_line(const char __user *src, size_t len,
>>>> +					  char ***argv, int *argc)
>>>> +{
>>>> +	char *cmd_buf, *cmd_buf_tmp;
>>>> +
>>>> +	cmd_buf = memdup_user(src, len);
>>>> +	if (IS_ERR(cmd_buf))
>>>> +		return PTR_ERR(cmd_buf);
>>>> +	cmd_buf[len] = '\0';
>>>> +
>>>> +	/* the cmd_buf has a newline at the end of the command so
>>>> +	 * remove it
>>>> +	 */
>>>> +	cmd_buf_tmp = strchr(cmd_buf, '\n');
>>>> +	if (cmd_buf_tmp) {
>>>> +		*cmd_buf_tmp = '\0';
>>>> +		len = (size_t)cmd_buf_tmp - (size_t)cmd_buf;
>>>> +	}
>>>> +
>>>> +	*argv = argv_split(GFP_KERNEL, cmd_buf, argc);
>>>> +	kfree(cmd_buf);
>>>> +	if (!*argv)
>>>> +		return -ENOMEM;
>>>
>>> I haven't spotted a single caller wanting this full argc/argv parsing.
>>> Can we please not add this complexity until its really needed?
>>>    
>>
>> I can remove it, but I use it in all the _write functions. I use the
>> argc to make sure I'm only getting one value to a write and I use
>> argv[0] to deal with the value.
>>
>> Honestly I'm not sure how valuable it is to check for a single argument,
>> but I'm fairly certain our validation team will file a bug if they pass
>> more than one argument and something happens :)
> 
> Just eyeballing the code - you'd still accept
> 
>    echo -e 'val1\0val2' > file
> 
> right? :) Perhaps less like that validation would come up with that
> but even the standard debugfs implementations don't seem to care too
> much (example of bool file in netdevsim):
> 
> # cat bpf_bind_accept
> Y
> # echo 'nbla' > bpf_bind_accept
> # echo $?
> 0
> # cat bpf_bind_accept
> N
> 

Good point, changed

>> Examples of using argv are on lines 358 and 466 of ice_debugfs.c
>>
>> I'm open to changing it, just not sure to what
>>
>>>> +/**
>>>> + * ice_debugfs_module_read - read from 'module' file
>>>> + * @filp: the opened file
>>>> + * @buffer: where to write the data for the user to read
>>>> + * @count: the size of the user's buffer
>>>> + * @ppos: file position offset
>>>> + */
>>>> +static ssize_t ice_debugfs_module_read(struct file *filp, char __user *buffer,
>>>> +				       size_t count, loff_t *ppos)
>>>> +{
>>>> +	struct dentry *dentry = filp->f_path.dentry;
>>>> +	struct ice_pf *pf = filp->private_data;
>>>> +	int status, module;
>>>> +	char *data = NULL;
>>>> +
>>>> +	/* don't allow commands if the FW doesn't support it */
>>>> +	if (!ice_fwlog_supported(&pf->hw))
>>>> +		return -EOPNOTSUPP;
>>>> +
>>>> +	module = ice_find_module_by_dentry(pf, dentry);
>>>> +	if (module < 0) {
>>>> +		dev_info(ice_pf_to_dev(pf), "unknown module\n");
>>>> +		return -EINVAL;
>>>> +	}
>>>> +
>>>> +	data = vzalloc(ICE_AQ_MAX_BUF_LEN);
>>>> +	if (!data) {
>>>> +		dev_warn(ice_pf_to_dev(pf), "Unable to allocate memory for FW configuration!\n");
>>>> +		return -ENOMEM;
>>>
>>> Can we use seq_print() here? It should simplify the reading quite a bit,
>>> not sure how well it works with files that can also be written, tho.
>>>    
>>
>> I'm probably missing something here, but how do we get more simple than
>> snprintf? I have a function (ice_fwlog_print_module_cfg) that handles
>> whether the user has passed a single module ID or they want data on all
>> the modules, but it all boils down to snprintf.
> 
> You need to vzalloc() and worry about it overflowing.
> 
>> I could get rid of ice_fwlog_print_module_cfg() and replace it inline
>> with the if/else code if that would be clearer, but I'm not sure
>> seq_printf() is helpful because each file is a single quantum of
>> information (with the exception of the file that represents all the
>> modules). I created a special file to represent all the modules, but
>> maybe it's more confusing and I should get rid of it and just make the
>> users specify all of the modules in a script.
>>
>> Would that be easier? Then there is no if/else it's just a single snprintf.
> 
> The value of seq_print() here is the fact it will handle the memory
> allocation and copying to user space for you. Ignore the "seq"
> in the name.

Ah, I see your point now, thanks for the clarification. I've made this 
change to seq_printf() for printing the module info.

This brings up the question of whether I should use seq_printf() for all 
the other _read fucntions. It feels like a lot of extra code to do it 
for the other _read functions because they output so little info and we 
control the output so it seems to be overkill to use seq_printf() for 
those. What do you think?

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