linux-kernel - Re: [PATCH] usb: ehci: replace scnprintf() with sysfs

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Message-ID: <643db411-d72c-4542-82a2-056d7d745967@hammernet.be>
Date: Mon, 23 Jun 2025 10:56:12 +0200
From: Hendrik Hammernet <hendrik.hamerlinck@...mernet.be>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>,
 stern@...land.harvard.edu, gregkh@...uxfoundation.org
Cc: skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev,
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: ehci: replace scnprintf() with sysfs_emit()


On 6/20/25 21:56, Christophe JAILLET wrote:
> Le 19/06/2025 à 14:07, Hendrik Hamerlinck a écrit :
>> Per Documentation/filesystems/sysfs.rst, show() methods should only
>> use sysfs_emit() or sysfs_emit_at() when formatting values to be
>> returned to userspace.
>>
>> Convert the uses of scnprintf() in sysfs show() methods to
>> sysfs_emit() and sysfs_emit_at() for better safety and consistency.
>>
>> Signed-off-by: Hendrik Hamerlinck <hendrik.hamerlinck@...mernet.be>
>> ---
>>   drivers/usb/host/ehci-sysfs.c | 15 +++++----------
>>   1 file changed, 5 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/usb/host/ehci-sysfs.c b/drivers/usb/host/ehci-sysfs.c
>> index 8f75cb7b197c..3786e81b0ed9 100644
>> --- a/drivers/usb/host/ehci-sysfs.c
>> +++ b/drivers/usb/host/ehci-sysfs.c
>> @@ -12,21 +12,18 @@ static ssize_t companion_show(struct device *dev,
>>                     char *buf)
>>   {
>>       struct ehci_hcd        *ehci;
>> -    int            nports, index, n;
>> -    int            count = PAGE_SIZE;
>> -    char            *ptr = buf;
>> +    int            nports, index;
>> +    int            len = 0;
>>         ehci = hcd_to_ehci(dev_get_drvdata(dev));
>>       nports = HCS_N_PORTS(ehci->hcs_params);
>>         for (index = 0; index < nports; ++index) {
>>           if (test_bit(index, &ehci->companion_ports)) {
>> -            n = scnprintf(ptr, count, "%d\n", index + 1);
>> -            ptr += n;
>> -            count -= n;
>> +            len += sysfs_emit_at(buf, len, "%d\n", index + 1);
>>           }
>
> Nitpick: extra { } looks useless now.

I'm fairly new to kernel development. I checked the coding style guide and
indeed saw that the curly braces should be avoided if they are unnecessary.

Thanks for pointing that out. I'll fix it in the next revision.