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SubjectRe: [PATCH 2/4] lib/hexdump.c: Optionally suppress lines of filler bytes
On Wed 2019-04-10 13:17:18, Alastair D'Silva wrote:
> From: Alastair D'Silva <alastair@d-silva.org>
>
> Some buffers may only be partially filled with useful data, while the rest
> is padded (typically with 0x00 or 0xff).
>
> This patch introduces flags which allow lines of padding bytes to be
> suppressed, making the output easier to interpret: HEXDUMP_SUPPRESS_0X00,
> HEXDUMP_SUPPRESS_0XFF
>
> The first and last lines are not suppressed by default, so the function
> always outputs something. This behaviour can be further controlled with
> the HEXDUMP_SUPPRESS_FIRST & HEXDUMP_SUPPRESS_LAST flags.
>
> An inline wrapper function is provided for backwards compatibility with
> existing code, which maintains the original behaviour.
>

> diff --git a/lib/hexdump.c b/lib/hexdump.c
> index b8a164814744..2f3bafb55a44 100644
> --- a/lib/hexdump.c
> +++ b/lib/hexdump.c
> +void print_hex_dump_ext(const char *level, const char *prefix_str,
> + int prefix_type, int rowsize, int groupsize,
> + const void *buf, size_t len, u64 flags)
> {
> const u8 *ptr = buf;
> - int i, linelen, remaining = len;
> + int i, remaining = len;
> unsigned char linebuf[64 * 3 + 2 + 64 + 1];
> + bool first_line = true;
>
> if (rowsize != 16 && rowsize != 32 && rowsize != 64)
> rowsize = 16;
>
> for (i = 0; i < len; i += rowsize) {
> - linelen = min(remaining, rowsize);
> + bool skip = false;
> + int linelen = min(remaining, rowsize);
> +
> remaining -= rowsize;
>
> + if (flags & HEXDUMP_SUPPRESS_0X00)
> + skip = buf_is_all(ptr + i, linelen, 0x00);
> +
> + if (!skip && (flags & HEXDUMP_SUPPRESS_0XFF))
> + skip = buf_is_all(ptr + i, linelen, 0xff);
> +
> + if (first_line && !(flags & HEXDUMP_SUPPRESS_FIRST))
> + skip = false;
> +
> + if (remaining <= 0 && !(flags & HEXDUMP_SUPPRESS_LAST))
> + skip = false;
> +
> + if (skip)
> + continue;

IMHO, quietly skipping lines could cause a lot of confusion,
espcially when the address is not printed.

I wonder how it would look like when we print something like:

--- skipped XX lines full of 0x00 ---

Then we might even remove the SUPPRESS_FIRST, SUPPRESS_LAST
and the ambiguous QUIET flags.

> +
> + first_line = false;

This should be above the if (skip).

> +
> hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize,
> - linebuf, sizeof(linebuf), ascii);
> + linebuf, sizeof(linebuf),
> + flags & HEXDUMP_ASCII);
>
> switch (prefix_type) {
> case DUMP_PREFIX_ADDRESS:
> @@ -272,7 +316,7 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
> }
> }
> }
> -EXPORT_SYMBOL(print_hex_dump);
> +EXPORT_SYMBOL(print_hex_dump_ext);

We should still export even the original function that
is still used everywhere.

Best Regards,
Petr

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