On Fri, Jan 10, 2025 at 07:42:05PM +0100, Miquel Raynal wrote:
> When dumping long buffers (especially for debug purposes) it may be very
> convenient to sometimes avoid spitting all the lines of the buffer if
> the lines are identical. Typically on embedded devices, the console
> would be wired to a UART running at 115200 bauds, which makes the dumps
> very (very) slow. In this case, having a flag to avoid printing
> duplicated lines is handy.
>
> Example of a made up repetitive output:
> 0f 53 63 47 56 55 78 7a aa b7 8c ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff 01 2a 39 eb
>
> Same but with the flag enabled:
> 0f 53 63 47 56 55 78 7a aa b7 8c ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> *
> ff ff ff ff ff ff ff ff ff ff ff ff 01 2a 39 eb
Still thinking that it's not okay to leave the cases where hex_dump_to_buffer()
is being used for the similar. I would expect that to be modified as well.
As told in v1 thread this can be achieved using a context data, instead of
providing zillion fields, one of which may be a kind of CRC32 checksum that
makes this work without any additional allocation.
But I won't prevent you to go with this if you get a blessing from other
PRINTK/PRINTF maintainers/reviewers.
...
> #include <linux/types.h>
> +#include <linux/string.h>
Can we keep it ordered (to some extent)? I know that types.h is misplaced here.
> #include <linux/ctype.h>
> #include <linux/errno.h>
> #include <linux/kernel.h>
...
> + if (flags & DUMP_FLAG_SKIP_IDENTICAL_LINES) {
> + if (i && !memcmp(ptr + i, ptr + prev_i, linelen)) {
> + prev_i = i;
Can we rather use a hash function or so instead of memcmp()?
> + if (same_line)
> + continue;
> + same_line = true;
> + printk("%s*\n", level);
> + continue;
> + } else {
Redundant 'else'.
> + prev_i = i;
> + same_line = false;
> + }
> + }
Something like
unsigned long hcur, hprev = ~0; // any unrealistic init value
...
if (flags & DUMP_FLAG_SKIP_IDENTICAL_LINES) {
hcur = $HASH($LINE);
if (hcur == hprev) {
...
continue;
}
hprev = hcur;
}
--
With Best Regards,
Andy Shevchenko
