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Subject[PATCH v4 3/7] lib/hexdump.c: Optionally suppress lines of repeated bytes
Date
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 a flag to allow the supression of lines of repeated
bytes, which are replaced with '** Skipped %u bytes of value 0x%x **'

An inline wrapper function is provided for backwards compatibility with
existing code, which maintains the original behaviour.

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
---
include/linux/printk.h | 26 +++++++++---
lib/hexdump.c | 91 ++++++++++++++++++++++++++++++++++++------
2 files changed, 100 insertions(+), 17 deletions(-)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index cefd374c47b1..c0416d0eb9e2 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -7,6 +7,7 @@
#include <linux/kern_levels.h>
#include <linux/linkage.h>
#include <linux/cache.h>
+#include <linux/bits.h>

extern const char linux_banner[];
extern const char linux_proc_banner[];
@@ -481,13 +482,18 @@ enum {
DUMP_PREFIX_ADDRESS,
DUMP_PREFIX_OFFSET
};
+
extern int hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
int groupsize, char *linebuf, size_t linebuflen,
bool ascii);
+
+#define HEXDUMP_ASCII BIT(0)
+#define HEXDUMP_SUPPRESS_REPEATED BIT(1)
+
#ifdef CONFIG_PRINTK
-extern void print_hex_dump(const char *level, const char *prefix_str,
+extern 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, bool ascii);
+ const void *buf, size_t len, u32 flags);
#if defined(CONFIG_DYNAMIC_DEBUG)
#define print_hex_dump_bytes(prefix_str, prefix_type, buf, len) \
dynamic_hex_dump(prefix_str, prefix_type, 16, 1, buf, len, true)
@@ -496,18 +502,28 @@ extern void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
const void *buf, size_t len);
#endif /* defined(CONFIG_DYNAMIC_DEBUG) */
#else
-static inline void print_hex_dump(const char *level, const char *prefix_str,
+static inline 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, bool ascii)
+ const void *buf, size_t len, u32 flags)
{
}
static inline void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
const void *buf, size_t len)
{
}
-
#endif

+static __always_inline void print_hex_dump(const char *level,
+ const char *prefix_str,
+ int prefix_type, int rowsize,
+ int groupsize, const void *buf,
+ size_t len, bool ascii)
+{
+ print_hex_dump_ext(level, prefix_str, prefix_type, rowsize, groupsize,
+ buf, len, ascii ? HEXDUMP_ASCII : 0);
+}
+
+
#if defined(CONFIG_DYNAMIC_DEBUG)
#define print_hex_dump_debug(prefix_str, prefix_type, rowsize, \
groupsize, buf, len, ascii) \
diff --git a/lib/hexdump.c b/lib/hexdump.c
index 870c8cbff1e1..61dc625c32f5 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -212,8 +212,44 @@ int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
EXPORT_SYMBOL(hex_dump_to_buffer);

#ifdef CONFIG_PRINTK
+
+/**
+ * buf_is_all - Check if a buffer contains only a single byte value
+ * @buf: pointer to the buffer
+ * @len: the size of the buffer in bytes
+ * @val: outputs the value if if the bytes are identical
+ */
+static bool buf_is_all(const u8 *buf, size_t len, u8 *val_out)
+{
+ size_t i;
+ u8 val;
+
+ if (len <= 1)
+ return false;
+
+ val = buf[0];
+
+ for (i = 1; i < len; i++) {
+ if (buf[i] != val)
+ return false;
+ }
+
+ *val_out = val;
+ return true;
+}
+
+static void announce_skipped(const char *level, const char *prefix_str,
+ u8 val, size_t count)
+{
+ if (count == 0)
+ return;
+
+ printk("%s%s ** Skipped %lu bytes of value 0x%x **\n",
+ level, prefix_str, count, val);
+}
+
/**
- * print_hex_dump - print a text hex dump to syslog for a binary blob of data
+ * print_hex_dump_ext - dump a binary blob of data to syslog in hexadecimal
* @level: kernel log level (e.g. KERN_DEBUG)
* @prefix_str: string to prefix each line with;
* caller supplies trailing spaces for alignment if desired
@@ -224,6 +260,10 @@ EXPORT_SYMBOL(hex_dump_to_buffer);
* @buf: data blob to dump
* @len: number of bytes in the @buf
* @ascii: include ASCII after the hex output
+ * @flags: A bitwise OR of the following flags:
+ * HEXDUMP_ASCII: include ASCII after the hex output
+ * HEXDUMP_SUPPRESS_REPEATED: suppress repeated lines of identical
+ * bytes
*
* Given a buffer of u8 data, print_hex_dump() prints a hex + ASCII dump
* to the kernel log at the specified kernel log level, with an optional
@@ -234,22 +274,25 @@ EXPORT_SYMBOL(hex_dump_to_buffer);
* (optionally) ASCII output.
*
* E.g.:
- * print_hex_dump(KERN_DEBUG, "raw data: ", DUMP_PREFIX_ADDRESS,
- * 16, 1, frame->data, frame->len, true);
+ * print_hex_dump_ext(KERN_DEBUG, "raw data: ", DUMP_PREFIX_ADDRESS,
+ * 16, 1, frame->data, frame->len, HEXDUMP_ASCII);
*
* Example output using %DUMP_PREFIX_OFFSET and 1-byte mode:
* 0009ab42: 40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f @ABCDEFGHIJKLMNO
* Example output using %DUMP_PREFIX_ADDRESS and 4-byte mode:
* ffffffff88089af0: 73727170 77767574 7b7a7978 7f7e7d7c pqrstuvwxyz{|}~.
*/
-void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
- int rowsize, int groupsize,
- const void *buf, size_t len, bool ascii)
+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, u32 flags)
{
const u8 *ptr = buf;
- int i, linelen, remaining = len;
+ int i, remaining = len;
unsigned char *linebuf;
unsigned int linebuf_len;
+ u8 skipped_val = 0;
+ size_t skipped = 0;
+

if (rowsize % groupsize)
rowsize -= rowsize % groupsize;
@@ -267,11 +310,35 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
}

for (i = 0; i < len; i += rowsize) {
- linelen = min(remaining, rowsize);
+ int linelen = min(remaining, rowsize);
remaining -= rowsize;

+ if (flags & HEXDUMP_SUPPRESS_REPEATED) {
+ u8 new_val;
+
+ if (buf_is_all(ptr + i, linelen, &new_val)) {
+ if (new_val == skipped_val) {
+ skipped += linelen;
+ continue;
+ } else {
+ announce_skipped(level, prefix_str,
+ skipped_val, skipped);
+ skipped_val = new_val;
+ skipped = linelen;
+ continue;
+ }
+ }
+ }
+
+ if (skipped) {
+ announce_skipped(level, prefix_str, skipped_val,
+ skipped);
+ skipped = 0;
+ }
+
hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize,
- linebuf, linebuf_len, ascii);
+ linebuf, linebuf_len,
+ flags & HEXDUMP_ASCII);

switch (prefix_type) {
case DUMP_PREFIX_ADDRESS:
@@ -289,7 +356,7 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,

kfree(linebuf);
}
-EXPORT_SYMBOL(print_hex_dump);
+EXPORT_SYMBOL(print_hex_dump_ext);

#if !defined(CONFIG_DYNAMIC_DEBUG)
/**
@@ -307,8 +374,8 @@ EXPORT_SYMBOL(print_hex_dump);
void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
const void *buf, size_t len)
{
- print_hex_dump(KERN_DEBUG, prefix_str, prefix_type, 16, 1,
- buf, len, true);
+ print_hex_dump_ext(KERN_DEBUG, prefix_str, prefix_type, 16, 1,
+ buf, len, HEXDUMP_ASCII);
}
EXPORT_SYMBOL(print_hex_dump_bytes);
#endif /* !defined(CONFIG_DYNAMIC_DEBUG) */
--
2.21.0
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