On Thu, Jul 12, 2018 at 08:40:55PM +0100, Chris Wilson wrote:
> Quoting Jordan Crouse (2018-07-12 19:59:19)
> > Add a drm printer suitable for use with the read callback for
> > devcoredump or other suitable buffer based output format that
> > isn't otherwise covered by seq_file.
> >
> > Signed-off-by: Jordan Crouse <jcrouse@xxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/drm_print.c | 74 +++++++++++++++++++++++++++++++++++++
> > include/drm/drm_print.h | 27 ++++++++++++++
> > 2 files changed, 101 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_print.c b/drivers/gpu/drm/drm_print.c
> > index b25f98f33f6c..03d1f98e5ac7 100644
> > --- a/drivers/gpu/drm/drm_print.c
> > +++ b/drivers/gpu/drm/drm_print.c
> > @@ -30,6 +30,80 @@
> > #include <drm/drmP.h>
> > #include <drm/drm_print.h>
> >
> > +void __drm_printfn_coredump(struct drm_printer *p, struct va_format *vaf)
> > +{
> > + struct drm_print_iterator *iterator = p->arg;
> > + ssize_t len;
> > +
> > + if (!iterator->remain)
> > + return;
> > +
> > + /* Figure out how big the string will be */
> > + len = snprintf(NULL, 0, "%pV", vaf);
>
> I was thinking there's some duplication here (kmalloc + snprintf) that
> could be reduced to kasprintf here. Is avoiding that allocation
> important or frequent enough to merit open coding?
> It's pity the kernel's printk doesn't support %n, so that leaves with
>
> buf = kasprintf(GFP_... , "%pV", vaf);
> if (!buf)
> return;
>
> len = strlen(buf);
>
> and even the copy + increment looks like it can then be factored to share
> more code.
I did a quick test - using kasprintf() unconditionally increased the total
time in my use case by about 4x. I think this was mainly due to this case:
if (iterator->offset + len <= iterator->start) {
....
return;
}
That said, I was able to organize the code so that we can reuse much of the
same code for both the printf and puts funcs which saves us a bit of churn
later.
Jordan
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