hexdump: remove the trailing space

For example:
        hex_dump_to_buffer("AB", 2, 16, 1, buf, 100, 0);
        pr_info("[%s]\n", buf);

I'd expect the output to be "[41 42]", but actually it's "[41 42 ]"

This patch also makes the required buf to be minimum.  To print the hex
format of "AB", a buf with size 6 should be sufficient, but
hex_dump_to_buffer() required at least 8.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/hexdump.c

@@ -65,7 +65,8 @@ void hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
 
 		for (j = 0; j < ngroups; j++)
 			lx += scnprintf(linebuf + lx, linebuflen - lx,
-				"%16.16llx ", (unsigned long long)*(ptr8 + j));
+				"%s%16.16llx", j ? " " : "",
+				(unsigned long long)*(ptr8 + j));
 		ascii_column = 17 * ngroups + 2;
 		break;
 	}
@@ -76,7 +77,7 @@ void hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
 
 		for (j = 0; j < ngroups; j++)
 			lx += scnprintf(linebuf + lx, linebuflen - lx,
-				"%8.8x ", *(ptr4 + j));
+				"%s%8.8x", j ? " " : "", *(ptr4 + j));
 		ascii_column = 9 * ngroups + 2;
 		break;
 	}
@@ -87,19 +88,21 @@ void hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
 
 		for (j = 0; j < ngroups; j++)
 			lx += scnprintf(linebuf + lx, linebuflen - lx,
-				"%4.4x ", *(ptr2 + j));
+				"%s%4.4x", j ? " " : "", *(ptr2 + j));
 		ascii_column = 5 * ngroups + 2;
 		break;
 	}
 
 	default:
-		for (j = 0; (j < rowsize) && (j < len) && (lx + 4) < linebuflen;
-		     j++) {
+		for (j = 0; (j < len) && (lx + 3) <= linebuflen; j++) {
 			ch = ptr[j];
 			linebuf[lx++] = hex_asc_hi(ch);
 			linebuf[lx++] = hex_asc_lo(ch);
 			linebuf[lx++] = ' ';
 		}
+		if (j)
+			lx--;
+
 		ascii_column = 3 * rowsize + 2;
 		break;
 	}
@@ -108,7 +111,7 @@ void hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
 
 	while (lx < (linebuflen - 1) && lx < (ascii_column - 1))
 		linebuf[lx++] = ' ';
-	for (j = 0; (j < rowsize) && (j < len) && (lx + 2) < linebuflen; j++)
+	for (j = 0; (j < len) && (lx + 2) < linebuflen; j++)
 		linebuf[lx++] = (isascii(ptr[j]) && isprint(ptr[j])) ? ptr[j]
 				: '.';
 nil: