Re: [PATCH v3 2/4] fsi: occ: Store the SBEFIFO FFDC in the user response buffer

[Eddie James <eajames@xxxxxxxxxxxxx>]

On 10/15/21 12:05 AM, Joel Stanley wrote:
> On Mon, 27 Sept 2021 at 15:59, Eddie James <eajames@xxxxxxxxxxxxx> wrote:
> > If the SBEFIFO response indicates an error, store the response in the
> > user buffer and return an error. Previously, the user had no way of
> > obtaining the SBEFIFO FFDC.
> How does this look for userspace?


The user's buffer now contains data in the event of a failure. No change 
in the event of a successful transfer.


> Will existing userspace handle this?


Yes, unless a poorly-designed application is relying on the data being 
the same after a failed transfer... In that case I would argue that the 
application should be fixed.


> > Signed-off-by: Eddie James <eajames@xxxxxxxxxxxxx>
> > ---
> > Changes since v1:
> >   - Don't store any magic value; only return non-zero resp_len in the error
> >     case if there is FFDC
> >
> >   drivers/fsi/fsi-occ.c | 66 ++++++++++++++++++++++++++++++-------------
> >   1 file changed, 47 insertions(+), 19 deletions(-)
> >
> > diff --git a/drivers/fsi/fsi-occ.c b/drivers/fsi/fsi-occ.c
> > index ace3ec7767e5..1d5f6fdc2a34 100644
> > --- a/drivers/fsi/fsi-occ.c
> > +++ b/drivers/fsi/fsi-occ.c
> > @@ -55,6 +55,9 @@ struct occ {
> >          int idx;
> >          u8 sequence_number;
> >          void *buffer;
> > +       void *client_buffer;
> > +       size_t client_buffer_size;
> > +       size_t client_response_size;
> >          enum versions version;
> >          struct miscdevice mdev;
> >          struct mutex occ_lock;
> > @@ -217,6 +220,20 @@ static const struct file_operations occ_fops = {
> >          .release = occ_release,
> >   };
> >
> > +static void occ_save_ffdc(struct occ *occ, __be32 *resp, size_t parsed_len,
> > +                         size_t resp_len)
> > +{
> > +       size_t dh = resp_len - parsed_len;
> Is there any chance that parsed_len is larger than resp_len?


No, based on the sbefifo_parse_status function.


> > +       size_t ffdc_len = (dh - 1) * 4;
> > +       __be32 *ffdc = &resp[resp_len - dh];
> Should you be checking that this number is sensible?


Do you mean ffdc_len or (resp_len - dh)? I was basing all this on the 
sbefifo_parse_status code, but I see that obviously:

resp_len - dh = resp_len - (resp_len - parsed_len) = parsed_len

So I will simplify.

As for ffdc_len, it is conceivable that dh is 0, so I will add a check 
for that.



Thanks Joel!

Eddie


> > +
> > +       if (ffdc_len > occ->client_buffer_size)
> > +               ffdc_len = occ->client_buffer_size;
> > +
> > +       memcpy(occ->client_buffer, ffdc, ffdc_len);
> > +       occ->client_response_size = ffdc_len;
> > +}