Re: [PATCH] USB: serial: add port statistics

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Sep 18, 2019 at 01:51:29PM +0200, Yegor Yefremov wrote:
> On Wed, Sep 18, 2019 at 1:45 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Wed, Sep 18, 2019 at 01:22:42PM +0200, Yegor Yefremov wrote:
> > > On Wed, Sep 18, 2019 at 1:08 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > >
> > > > On Wed, Sep 18, 2019 at 11:14:15AM +0200, yegorslists@googlemail.com wrote:
> > > > > From: Yegor Yefremov <yegorslists@googlemail.com>
> > > > >
> > > > > Add additional port statistics like received and transmitted bytes
> > > > > the way /proc/tty/driver/serial does.
> > > > >
> > > > > As usbserial driver already provides USB related information and
> > > > > this line is longer than 100 characters, this patch adds an
> > > > > additional line with the same port number:
> > > > >
> > > > > 0: module:ftdi_sio name:"FTDI USB Serial Device" vendor:0403 ...
> > > > > 0: tx:112 rx:0
> > > > >
> > > > > Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
> > > > > ---
> > > > >  drivers/usb/serial/usb-serial.c | 22 ++++++++++++++++++++++
> > > > >  1 file changed, 22 insertions(+)
> > > >
> > > > You can't change existing proc files without having the chance that
> > > > userspace tools will break.
> > > >
> > > > Have you tried this and seen what dies a horrible death?
> > >
> > > This patch is more a proof of concept (forgot to add RFC keyword). I
> > > find statistics provdes by the 8250 driver very useful for debugging
> > > purposes. What would be the best way to implemnt this feature for
> > > usbserial driver?
> > >
> > > a) extend current line:
> > >
> > > 0: module:ftdi_sio name:"FTDI USB Serial Device" vendor:0403 ...tx:112 rx:0
> > >
> > > though this still can break parsing
> > >
> > > b) creating special entries for FTDI and other UARTs? Though it would
> > > be greate to have all usbserial UART handled the same way in the same
> > > file
> >
> > Why is any of this needed at all?  Also, be very aware of the security
> > issues involved here, we had to disable access of these values by
> > "normal" users for other tty devices, so please don't break that by
> > offering it up here again.
> >
> > What is going to use this information?
> 
> This feature is not a "must have" one but it is convenient to see
> transferred/received bytes and error flags from user space. If some
> serial software is not working like expected and doesn't provide
> enough debugging information one can quickly look at port statistics
> from the console in order to check whether and how many bytes were
> transferred or whether the were some communication errors.

Again, it's a security issue, so be careful about this.  If you _REALLY_
need it, make it a debugfs file, readble by root only.

Or a tracepoint, and then you can have a userspace read the data using
ebpf :)

thanks,

greg k-h