[PATCH v4 2/3] drm/printer: Allow NULL data in devcoredump printer

[Matthew Brost]

On Thu, Aug 01, 2024 at 08:00:21AM -0600, Cavitt, Jonathan wrote:
> -----Original Message-----
> From: Brost, Matthew <matthew.brost at intel.com> 
> Sent: Wednesday, July 31, 2024 5:03 PM
> To: Cavitt, Jonathan <jonathan.cavitt at intel.com>
> Cc: intel-xe at lists.freedesktop.org; dri-devel at lists.freedesktop.org; maarten.lankhorst at linux.intel.com; Vivi, Rodrigo <rodrigo.vivi at intel.com>
> Subject: Re: [PATCH v4 2/3] drm/printer: Allow NULL data in devcoredump printer
> > 
> > On Wed, Jul 31, 2024 at 04:22:03PM -0600, Cavitt, Jonathan wrote:
> > > -----Original Message-----
> > > From: Intel-xe <intel-xe-bounces at lists.freedesktop.org> On Behalf Of Matthew Brost
> > > Sent: Wednesday, July 31, 2024 2:32 PM
> > > To: intel-xe at lists.freedesktop.org; dri-devel at lists.freedesktop.org
> > > Cc: maarten.lankhorst at linux.intel.com; Vivi, Rodrigo <rodrigo.vivi at intel.com>
> > > Subject: [PATCH v4 2/3] drm/printer: Allow NULL data in devcoredump printer
> > > > 
> > > > Useful to determine size of devcoreump before writing it out.
> > > > 
> > > > Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> > > > Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> > > 
> > > It seems this patch prevents us from copying strings into the data field if the data
> > > field hasn't been initialized.  I'm not certain if it could ever be uninitialized at this
> > > point, but I recognize it as good practice to check just in case regardless.
> > > 
> > 
> > That's not the intent. The intent to call the print functions with NULL
> > data so the printer can calculate the size of buffer required to print
> > out all the devcoredump data.
> 
> So if iterator->data is NULL, you want to NOT copy into it?
> -Jonathan Cavitt

Yes, exactly. Run devcoredump printer with NULL data to get size, alloc
data based on devcoredump printer offset, run it again with a valid data
pointer to print.

Matt

> 
> > 
> > Matt
> > 
> > > Reviewed-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
> > > -Jonathan Cavitt
> > > 
> > > > ---
> > > >  drivers/gpu/drm/drm_print.c | 13 ++++++++-----
> > > >  1 file changed, 8 insertions(+), 5 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> > > > index cf24dfdeb6b2..a1a4de9f9c44 100644
> > > > --- a/drivers/gpu/drm/drm_print.c
> > > > +++ b/drivers/gpu/drm/drm_print.c
> > > > @@ -100,8 +100,9 @@ void __drm_puts_coredump(struct drm_printer *p, const char *str)
> > > >  			copy = iterator->remain;
> > > >  
> > > >  		/* Copy out the bit of the string that we need */
> > > > -		memcpy(iterator->data,
> > > > -			str + (iterator->start - iterator->offset), copy);
> > > > +		if (iterator->data)
> > > > +			memcpy(iterator->data,
> > > > +				str + (iterator->start - iterator->offset), copy);
> > > >  
> > > >  		iterator->offset = iterator->start + copy;
> > > >  		iterator->remain -= copy;
> > > > @@ -110,7 +111,8 @@ void __drm_puts_coredump(struct drm_printer *p, const char *str)
> > > >  
> > > >  		len = min_t(ssize_t, strlen(str), iterator->remain);
> > > >  
> > > > -		memcpy(iterator->data + pos, str, len);
> > > > +		if (iterator->data)
> > > > +			memcpy(iterator->data + pos, str, len);
> > > >  
> > > >  		iterator->offset += len;
> > > >  		iterator->remain -= len;
> > > > @@ -140,8 +142,9 @@ void __drm_printfn_coredump(struct drm_printer *p, struct va_format *vaf)
> > > >  	if ((iterator->offset >= iterator->start) && (len < iterator->remain)) {
> > > >  		ssize_t pos = iterator->offset - iterator->start;
> > > >  
> > > > -		snprintf(((char *) iterator->data) + pos,
> > > > -			iterator->remain, "%pV", vaf);
> > > > +		if (iterator->data)
> > > > +			snprintf(((char *) iterator->data) + pos,
> > > > +				iterator->remain, "%pV", vaf);
> > > >  
> > > >  		iterator->offset += len;
> > > >  		iterator->remain -= len;
> > > > -- 
> > > > 2.34.1
> > > > 
> > > > 
> >