[PATCH v3 1/2] hexdump: minimize the output width of the offset

[thunder . leizhen]

From: Zhen Lei <thunder.leizhen@xxxxxxxxxx>

The offset of case DUMP_PREFIX_OFFSET always starts from 0. Currently,
the output width is fixed to 8. But we usually dump only tens or hundreds
of bytes, occasionally thousands of bytes. Therefore, the output offset
value always has a number of leading zeros, which increases the number of
bytes printed and reduces readability. Let's minimize the output width of
the offset based on the number of significant bits of its maximum value.

Before:
dump_size=36:
00000000: c0 ba 8c 80 00 80 ff ff 6c 93 ee 2f ee bf ff ff
00000010: 00 50 1e 98 ff 27 ff ff 01 00 00 00 00 00 00 00
00000020: 80 ca 2f 98

After:
dump_size=8:
0: c0 ba 89 80 00 80 ff ff

dump_size=36:
00: c0 3a 91 80 00 80 ff ff 6c 93 ae 76 30 ce ff ff
10: 00 60 cd 60 7d 4e ff ff 01 00 00 00 00 00 00 00
20: 40 9e 29 40

dump_size=300:
000: c0 ba 8d 80 00 80 ff ff 6c 93 ce d4 78 a7 ff ff
010: 00 00 16 18 0c 40 ff ff 01 00 00 00 00 00 00 00
020: 01 00 00 00 00 00 00 00 e8 bc 8d 80 00 80 ff ff
... ...
110: 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
120: 00 08 12 01 0c 40 ff ff 00 00 01 00

Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
Reviewed-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
---
 lib/hexdump.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/hexdump.c b/lib/hexdump.c
index 06833d404398d74..1064706d57c15ed 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -263,7 +263,7 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
 		    const void *buf, size_t len, bool ascii)
 {
 	const u8 *ptr = buf;
-	int i, linelen, remaining = len;
+	int i, linelen, width = 0, remaining = len;
 	unsigned char linebuf[32 * 3 + 2 + 32 + 1];
 
 	if (rowsize != 16 && rowsize != 32)
@@ -282,7 +282,15 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
 			       level, prefix_str, ptr + i, linebuf);
 			break;
 		case DUMP_PREFIX_OFFSET:
-			printk("%s%s%.8x: %s\n", level, prefix_str, i, linebuf);
+			if (!width) {
+				unsigned long tmp = len - 1; /* offset start from 0, so minus 1 */
+
+				do {
+					width++;
+					tmp >>= 4;
+				} while (tmp);
+			}
+			printk("%s%s%0*x: %s\n", level, prefix_str, width, i, linebuf);
 			break;
 		default:
 			printk("%s%s%s\n", level, prefix_str, linebuf);
-- 
2.34.1