[PATCH v2 1/2] seq_buf: Add printing formatted hex dumps

[Piotr Maziarz <piotrx.maziarz@linux.intel.com>]

Provided function is an analogue of print_hex_dump().

Implementing this function in seq_buf allows using for multiple
purposes (e.g. for tracing) and therefore prevents from code duplication
in every layer that uses seq_buf.

print_hex_dump() is an essential part of logging data to dmesg. Adding
similar capability for other purposes is beneficial to all users.

Example usage:
seq_buf_hex_dump(seq, "", DUMP_PREFIX_OFFSET, 16, 4, buf,
		 ARRAY_SIZE(buf), true);
Example output:
00000000: 00000000 ffffff10 ffffff32 ffff3210  ........2....2..
00000010: ffff3210 83d00437 c0700000 00000000  .2..7.....p.....
00000020: 02010004 0000000f 0000000f 00004002  .............@..
00000030: 00000fff 00000000                    ........

Signed-off-by: Piotr Maziarz <piotrx.maziarz@linux.intel.com>
Signed-off-by: Cezary Rojewski <cezary.rojewski@intel.com>
---
v2
Add kernel doc header
Explain linebuf magic number size

Decided not to change declaration order or remaining -= rowsize to
remaining -= linelen in order to stay aligned with base print_hex_dump
function. However I can change it if requested.

 include/linux/seq_buf.h |  3 +++
 lib/seq_buf.c           | 62 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
index aa5deb0..fb0205d 100644
--- a/include/linux/seq_buf.h
+++ b/include/linux/seq_buf.h
@@ -125,6 +125,9 @@ extern int seq_buf_putmem(struct seq_buf *s, const void *mem, unsigned int len);
 extern int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
 			      unsigned int len);
 extern int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc);
+extern int seq_buf_hex_dump(struct seq_buf *s, const char *prefix_str,
+			    int prefix_type, int rowsize, int groupsize,
+			    const void *buf, size_t len, bool ascii);
 
 #ifdef CONFIG_BINARY_PRINTF
 extern int
diff --git a/lib/seq_buf.c b/lib/seq_buf.c
index bd807f5..4e865d4 100644
--- a/lib/seq_buf.c
+++ b/lib/seq_buf.c
@@ -328,3 +328,65 @@ int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, int cnt)
 	s->readpos += cnt;
 	return cnt;
 }
+
+/**
+ * seq_buf_hex_dump - print formatted hex dump into the sequence buffer
+ * @s: seq_buf descriptor
+ * @prefix_str: string to prefix each line with;
+ *  caller supplies trailing spaces for alignment if desired
+ * @prefix_type: controls whether prefix of an offset, address, or none
+ *  is printed (%DUMP_PREFIX_OFFSET, %DUMP_PREFIX_ADDRESS, %DUMP_PREFIX_NONE)
+ * @rowsize: number of bytes to print per line; must be 16 or 32
+ * @groupsize: number of bytes to print at a time (1, 2, 4, 8; default = 1)
+ * @buf: data blob to dump
+ * @len: number of bytes in the @buf
+ * @ascii: include ASCII after the hex output
+ *
+ * Function is an analogue of print_hex_dump() and thus has similar interface.
+ *
+ * linebuf size is maximal length for one line.
+ * 32 * 3 - maximum bytes per line, each printed into 2 chars + 1 for
+ *	separating space
+ * 2 - spaces separating hex dump and ascii representation
+ * 32 - ascii representation
+ * 1 - terminating '\0'
+ *
+ * Returns zero on success, -1 on overflow
+ */
+int seq_buf_hex_dump(struct seq_buf *s, const char *prefix_str, int prefix_type,
+		     int rowsize, int groupsize,
+		     const void *buf, size_t len, bool ascii)
+{
+	const u8 *ptr = buf;
+	int i, linelen, remaining = len;
+	unsigned char linebuf[32 * 3 + 2 + 32 + 1];
+	int ret;
+
+	if (rowsize != 16 && rowsize != 32)
+		rowsize = 16;
+
+	for (i = 0; i < len; i += rowsize) {
+		linelen = min(remaining, rowsize);
+		remaining -= rowsize;
+
+		hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize,
+				   linebuf, sizeof(linebuf), ascii);
+
+		switch (prefix_type) {
+		case DUMP_PREFIX_ADDRESS:
+			ret = seq_buf_printf(s, "%s%p: %s\n",
+			       prefix_str, ptr + i, linebuf);
+			break;
+		case DUMP_PREFIX_OFFSET:
+			ret = seq_buf_printf(s, "%s%.8x: %s\n",
+					     prefix_str, i, linebuf);
+			break;
+		default:
+			ret = seq_buf_printf(s, "%s%s\n", prefix_str, linebuf);
+			break;
+		}
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
-- 
2.7.4