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

[Cavitt, Jonathan]

-----Original Message-----
From: Brost, Matthew <matthew.brost at intel.com> 
Sent: Thursday, August 1, 2024 7:30 AM
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 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.

Okay, I think I understand.  That might be good to add to the commit message,
then.  Something like:

"""
We want to determine the size of the devcoredump before writing it out.
To that end, we will run the devcoredump printer with NULL data to get
the size, alloc data based on the generated offset, then run the
devcorecump again with a valid data pointer to print.  This necessitates
not writing data to the data pointer on the initial pass, when it is NULL.
"""

Maybe that's a bit overboard?  In either case, my RB still stands,
regardless of if the commit message is updated or not.
-Jonathan Cavitt

> 
> 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
> > > > > 
> > > > > 
> > > 
>