Re: [PATCH v3 3/7] kunit: Handle logging of lines longer than the fragment buffer size

[Richard Fitzgerald]

On 10/8/23 15:38, David Gow wrote:
> On Wed, 9 Aug 2023 at 23:54, Richard Fitzgerald
> <rf@xxxxxxxxxxxxxxxxxxxxx> wrote:
> > Add handling to kunit_log_append() for log messages that are longer than
> > a single buffer fragment.
> >
> > The initial implementation of fragmented buffers did not change the logic
> > of the original kunit_log_append(). A consequence was that it still had
> > the original assumption that a log line will fit into one buffer.
> >
> > This patch checks for log messages that are larger than one fragment
> > buffer. In that case, kvasprintf() is used to format it into a temporary
> > buffer and that content is then split across as many fragments as
> > necessary.
> >
> > Signed-off-by: Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx>
> > ---
>
> I think this looks good (and is a long-overdue addition to the logging
> functionality).
>
> One thought I have (and I'm kicking myself for not thinking of it
> earlier) is that this is starting to get very similar to the "string
> stream" functionality in lib/kunit/string-stream.{h,c}. Now, I
> actually think this implementation is much more efficient (using
> larger fragments, whereas the string stream uses variable-sized ones).
> Particularly since there are a lot of cases where string streams are
> created, converted to a string, and then logged, there's almost
> certainly a bunch of redundant work being done here.
>
> My gut feeling is that we should stick with this as-is, and maybe try
> to either work out some better integration between string streams and
> logging (to avoid that extra string allocation) or find some way of
> combining them.

I completely failed to notice string_stream. I could re-implement this
to use string_stream. I wonder whether appending newlines gets
a bit inefficient with the current string_stream implementation.
Could add newline support to string_stream and alloc one extra byte for
each fragment just in case we need to add a newline.

The string_stream implementation would waste a lot a memory if you log
many short lines. My current code wastes memory if you log lots of lines
that don't fit in available space in the current fragment - though it's
simple to shuffle the formatted string backwards to fill up the previous
fragment (I just haven't done that yet).