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Message-ID: <faa45811-367f-40bd-ad95-f6f08fdf2603@linux.dev>
Date: Thu, 15 Aug 2024 14:40:33 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Jiri Slaby <jirislaby@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Vadim Fedorenko <vadfed@...a.com>
Cc: Jakub Kicinski <kuba@...nel.org>,
Jonathan Lemon <jonathan.lemon@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net v2 1/2] ptp: ocp: adjust sysfs entries to expose tty
information
On 14/08/2024 11:30, Jiri Slaby wrote:
> On 14. 08. 24, 10:37, Vadim Fedorenko wrote:
>> On 14/08/2024 06:00, Jiri Slaby wrote:
>>> On 13. 08. 24, 20:24, Vadim Fedorenko wrote:
>>>> On 13/08/2024 10:33, Greg Kroah-Hartman wrote:
>>>>> On Mon, Aug 05, 2024 at 03:04:59PM -0700, Vadim Fedorenko wrote:
>>>>>> Starting v6.8 the serial port subsystem changed the hierarchy of
>>>>>> devices
>>>>>> and symlinks are not working anymore. Previous discussion made it
>>>>>> clear
>>>>>> that the idea of symlinks for tty devices was wrong by design.
>>>>>> Implement
>>>>>> additional attributes to expose the information. Fixes tag points
>>>>>> to the
>>>>>> commit which introduced the change.
>>>>>>
>>>>>> Fixes: b286f4e87e32 ("serial: core: Move tty and serdev to be
>>>>>> children of serial core port device")
>>>>>> Signed-off-by: Vadim Fedorenko <vadfed@...a.com>
>>>>>> ---
>>>>>> drivers/ptp/ptp_ocp.c | 68 ++++++++++++++++++++++++++++++++
>>>>>> +----------
>>>>>> 1 file changed, 52 insertions(+), 16 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
>>>>>> index ee2ced88ab34..7a5026656452 100644
>>>>>> --- a/drivers/ptp/ptp_ocp.c
>>>>>> +++ b/drivers/ptp/ptp_ocp.c
>>>>>> @@ -3346,6 +3346,55 @@ static EXT_ATTR_RO(freq, frequency, 1);
>>>>>> static EXT_ATTR_RO(freq, frequency, 2);
>>>>>> static EXT_ATTR_RO(freq, frequency, 3);
>>>>>> +static ssize_t
>>>>>> +ptp_ocp_tty_show(struct device *dev, struct device_attribute
>>>>>> *attr, char *buf)
>>>>>> +{
>>>>>> + struct dev_ext_attribute *ea = to_ext_attr(attr);
>>>>>> + struct ptp_ocp *bp = dev_get_drvdata(dev);
>>>>>> + struct ptp_ocp_serial_port *port;
>>>>>> +
>>>>>> + port = (void *)((uintptr_t)bp + (uintptr_t)ea->var);
>>>>>
>>>>> That's insane pointer math, how do we know this is correct?
>>>>>
>>>>>> + return sysfs_emit(buf, "ttyS%d", port->line);
>>>>>> +}
>>>>>> +
>>>>>> +static umode_t
>>>>>> +ptp_ocp_timecard_tty_is_visible(struct kobject *kobj, struct
>>>>>> attribute *attr, int n)
>>>>>> +{
>>>>>> + struct ptp_ocp *bp = dev_get_drvdata(kobj_to_dev(kobj));
>>>>>> + struct ptp_ocp_serial_port *port;
>>>>>> + struct device_attribute *dattr;
>>>>>> + struct dev_ext_attribute *ea;
>>>>>> +
>>>>>> + if (strncmp(attr->name, "tty", 3))
>>>>>> + return attr->mode;
>>>>>> +
>>>>>> + dattr = container_of(attr, struct device_attribute, attr);
>>>>>> + ea = container_of(dattr, struct dev_ext_attribute, attr);
>>>>>> + port = (void *)((uintptr_t)bp + (uintptr_t)ea->var);
>>>>>
>>>>> That's crazy pointer math, how are you ensured that it is correct?
>>>>> Why
>>>>> isn't there a container_of() thing here instead?
>>>>
>>>> Well, container_of cannot be used here because the attributes are
>>>> static
>>>> while the function reads dynamic instance. The only values that are
>>>> populated into the attributes of the group are offsets.
>>>> But I can convert it to a helper which will check that the offset
>>>> provided is the real offset of the structure we expect. And it could
>>>> be reused in both "is_visible" and "show" functions.
>>>
>>> Strong NACK against this approach.
>>>
>>> What about converting those 4 ports into an array and adding an enum
>>> { PORT_GNSS, POTR_GNSS2, PORT_MAC, PORT_NMEA }?
>>
>> Why is it a problem? I don't see big difference between these 2
>> implementations:
>>
>> struct ptp_ocp_serial_port *get_port(struct ptp_ocp *bp, void *offset)
>> {
>> switch((uintptr_t)offset) {
>> case offsetof(struct ptp_ocp, gnss_port):
>> return &bp->gnss_port;
>> case offsetof(struct ptp_ocp, gnss2_port):
>> return &bp->gnss2_port;
>> case offsetof(struct ptp_ocp, mac_port):
>> return &bp->mac_port;
>> case offsetof(struct ptp_ocp, nmea_port):
>> return &bp->nmea_port;
>> }
>> return NULL;
>> }
>>
>> and:
>>
>> struct ptp_ocp_serial_port *get_port(struct ptp_ocp *bp, void *offset)
>> {
>> switch((enum port_type)offset) {
>> case PORT_GNSS:
>> return &bp->tty_port[PORT_GNSS];
>> case PORT_GNSS2:
>> return &bp->tty_port[PORT_GNSS2];
>> case PORT_MAC:
>> return &bp->tty_port[PORT_MAC];
>> case PORT_NMEA:
>> return &bp->tty_port[PORT_NMEA];
>> }
>> return NULL;
>> }
>>
>> The second option will require more LoC to change the initialization
>> part of the driver, but will not simplify the access.
>> If you suggest to use enum value directly, without the check, then
>> it will not solve the problem of checking the boundary, which Greg
>> refers to AFAIU.
>
> Why do you need this get_port() here at all? Simply doing bp-
> >tty_port[ea->var] as in already present attrs will do the job, right?
>
Alright, the v3 is up for review with this way applied,
thanks!
> thanks,
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