linux-kernel - Re: [PATCH 2/2] usb: storage: rearrange triple nested CSW data phase check

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Message-ID: <CACaw+eyo4Yc0=Ak=RWsozDVMzGHaZhW6SBHJUWFqRb6gPzWS8Q@mail.gmail.com>
Date: Wed, 29 Oct 2025 21:39:36 -0300
From: Desnes Nunes <desnesn@...hat.com>
To: Alan Stern <stern@...land.harvard.edu>
Cc: linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org, 
	gregkh@...uxfoundation.org
Subject: Re: [PATCH 2/2] usb: storage: rearrange triple nested CSW data phase check

Hello Alan,

On Wed, Oct 29, 2025 at 6:54 PM Alan Stern <stern@...land.harvard.edu> wrote:
>
> On Wed, Oct 29, 2025 at 04:14:14PM -0300, Desnes Nunes wrote:
> > This rearranges the triple nested CSW data phase if clause, in order to
> > make usb_stor_Bulk_transport() code more readlable. No functional change.
> >
> > Signed-off-by: Desnes Nunes <desnesn@...hat.com>
> > ---
> >  drivers/usb/storage/transport.c | 21 ++++++++++-----------
> >  1 file changed, 10 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
> > index 96b81cf6adc7..3f2e1df5ad1e 100644
> > --- a/drivers/usb/storage/transport.c
> > +++ b/drivers/usb/storage/transport.c
> > @@ -1188,18 +1188,17 @@ int usb_stor_Bulk_transport(struct scsi_cmnd *srb, struct us_data *us)
> >                * check whether it really is a CSW.
> >                */
> >               if (result == USB_STOR_XFER_SHORT &&
> > -                             srb->sc_data_direction == DMA_FROM_DEVICE &&
> > -                             transfer_length - scsi_get_resid(srb) ==
> > -                                     US_BULK_CS_WRAP_LEN) {
> > +                 srb->sc_data_direction == DMA_FROM_DEVICE &&
> > +                 transfer_length - scsi_get_resid(srb) == US_BULK_CS_WRAP_LEN) {
>
> This change has nothing to do with the subject of the patch.  Please
> leave the code the way it was.
>
> >                       struct scatterlist *sg = NULL;
> > -                     unsigned int offset = 0;
> > -
> > -                     if (usb_stor_access_xfer_buf((unsigned char *) bcs,
> > -                                     US_BULK_CS_WRAP_LEN, srb, &sg,
> > -                                     &offset, FROM_XFER_BUF) ==
> > -                                             US_BULK_CS_WRAP_LEN &&
> > -                                     bcs->Signature ==
> > -                                             cpu_to_le32(US_BULK_CS_SIGN)) {
> > +                     unsigned int offset = 0, buflen = 0;
>
> It seems silly to initialize buflen to 0 when the very next statement is
> going to overwrite that value.
>
> Also, "buflen" is not a good name for this variable, because the
> variable does not contain the length of a buffer.  Rather, it will
> contain the amount of data that got transferred by the
> usb_stor_access_xfer_buf() routine.  The following "if" statement then
> tests whether that amount is equal to the buffer length.
>
> Alan Stern

I tried to borrow some code from usb storage protocol, but after these
observations I do agree it is not a good name here.
Nonetheless, I will drop this patch from v2 as requested.

Thanks for the review,

-- 
Desnes Nunes