[2/4] lib/hexdump.c: Optionally suppress lines of filler bytes

Commit Message

Alastair D'Silva April 10, 2019, 3:17 a.m. UTC

From: Alastair D'Silva <[e-mail]>

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.

Signed-off-by: Alastair D'Silva <[e-mail]>
---
 include/linux/printk.h | 38 ++++++++++++++++++----
 lib/hexdump.c          | 72 ++++++++++++++++++++++++++++++++++--------
 2 files changed, 89 insertions(+), 21 deletions(-)

Comments

Alastair D'Silva April 10, 2019, 3:32 a.m. UTC | #1

On Wed, 2019-04-10 at 13:17 +1000, Alastair D'Silva wrote:
> From: Alastair D'Silva <[e-mail]>
> 
> 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.
> 
> Signed-off-by: Alastair D'Silva <[e-mail]>
> ---
> 
<snip>

> diff --git a/lib/hexdump.c b/lib/hexdump.c
> index b8a164814744..2f3bafb55a44 100644
> --- a/lib/hexdump.c
> +++ b/lib/hexdump.c
> @@ -209,8 +209,21 @@ int hex_dump_to_buffer(const void *buf, size_t
> len, int rowsize, int groupsize,
>  EXPORT_SYMBOL(hex_dump_to_buffer);
>  
>  #ifdef CONFIG_PRINTK
> +
> +static bool buf_is_all(const u8 *buf, size_t len, u8 val)
> +{
> +	size_t i;
> +
> +	for (i = 0; i < len; i++) {
> +		if (buf[i] != val)
> +			return false;
> +	}
> +
> +	return true;
> +}
> +
>  /**
> - * 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
> @@ -221,42 +234,73 @@ 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
This line should have been removed. I'll address it in V2.

> + * @flags: A bitwise OR of the following flags:
> + *	HEXDUMP_ASCII:		include ASCII after the hex output
> + *	HEXDUMP_SUPPRESS_0X00:	suppress lines that are all 0x00
> + *				(other than first or last)
> + *	HEXDUMP_SUPPRESS_0XFF:	suppress lines that are all 0xff
> + *				(other than first or last)
> + *	HEXDUMP_SUPPRESS_FIRST:	allows the first line to be
> suppressed
> + *	HEXDUMP_SUPPRESS_LAST:	allows the last line to be suppressed
> + *				If the first and last line may be
> suppressed,
> + *				an empty buffer will not produce any
> output
>   *
>   * 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
>   * leading prefix.
>   *
> - * print_hex_dump() works on one "line" of output at a time, i.e.,
> + * print_hex_dump_ext() works on one "line" of output at a time,
> i.e.,
>   * 16, 32 or 64 bytes of input data converted to hex + ASCII output.
> - * print_hex_dump() iterates over the entire input @buf, breaking it
> into
> + * print_hex_dump_ext() iterates over the entire input @buf,
> breaking it into
>   * "line size" chunks to format and print.
>   *
>   * 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{|}~.
>   */

Petr Mladek April 12, 2019, 2:03 p.m. UTC | #2

On Wed 2019-04-10 13:17:18, Alastair D'Silva wrote:
> From: Alastair D'Silva <[e-mail]>
> 
> 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

Alastair D'Silva April 12, 2019, 11:28 p.m. UTC | #3

> -----Original Message-----
> From: Petr Mladek <[e-mail]>
> Sent: Saturday, 13 April 2019 12:04 AM
> To: Alastair D'Silva <[e-mail]>
> Cc: [e-mail]; Jani Nikula <[e-mail]>;
Joonas
> Lahtinen <[e-mail]>; Rodrigo Vivi
> <[e-mail]>; David Airlie <[e-mail]>; Daniel Vetter
> <[e-mail]>; Karsten Keil <[e-mail]>; Jassi Brar
> <[e-mail]>; Tom Lendacky <[e-mail]>;
> David S. Miller <[e-mail]>; Jose Abreu
> <[e-mail]>; Kalle Valo <[e-mail]>;
> Stanislaw Gruszka <[e-mail]>; Benson Leung
> <[e-mail]>; Enric Balletbo i Serra
> <[e-mail]>; James E.J. Bottomley
> <[e-mail]>; Martin K. Petersen <[e-mail]>;
> Greg Kroah-Hartman <[e-mail]>; Alexander Viro
> <[e-mail]>; Sergey Senozhatsky
> <[e-mail]>; Steven Rostedt <[e-mail]>;
> Andrew Morton <[e-mail]>; intel-
> [e-mail]; [e-mail]; linux-
> [e-mail]; [e-mail];
> [e-mail]; [e-mail]; linux-
> [e-mail]; [e-mail];
> [e-mail]; [e-mail]
> Subject: Re: [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 <[e-mail]>
> >
> > 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.
>
It's up to the caller to decide how they want it displayed.

> I wonder how it would look like when we print something like:
> 
>     --- skipped XX lines full of 0x00 ---

This could be added as a later enhancement, with a new flag (eg.
HEXDUMP_SUPPRESS_VERBOSE).

> 
> 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.

It's replaced with an inline wrapper function, there's no need to export it.

Petr Mladek April 15, 2019, 9:18 a.m. UTC | #4

On Sat 2019-04-13 09:28:03, Alastair D'Silva wrote:
> > -----Original Message-----
> > From: Petr Mladek <[e-mail]>
> > Sent: Saturday, 13 April 2019 12:04 AM
> > To: Alastair D'Silva <[e-mail]>
> > Cc: [e-mail]; Jani Nikula <[e-mail]>;
> Joonas
> > Lahtinen <[e-mail]>; Rodrigo Vivi
> > <[e-mail]>; David Airlie <[e-mail]>; Daniel Vetter
> > <[e-mail]>; Karsten Keil <[e-mail]>; Jassi Brar
> > <[e-mail]>; Tom Lendacky <[e-mail]>;
> > David S. Miller <[e-mail]>; Jose Abreu
> > <[e-mail]>; Kalle Valo <[e-mail]>;
> > Stanislaw Gruszka <[e-mail]>; Benson Leung
> > <[e-mail]>; Enric Balletbo i Serra
> > <[e-mail]>; James E.J. Bottomley
> > <[e-mail]>; Martin K. Petersen <[e-mail]>;
> > Greg Kroah-Hartman <[e-mail]>; Alexander Viro
> > <[e-mail]>; Sergey Senozhatsky
> > <[e-mail]>; Steven Rostedt <[e-mail]>;
> > Andrew Morton <[e-mail]>; intel-
> > [e-mail]; [e-mail]; linux-
> > [e-mail]; [e-mail];
> > [e-mail]; [e-mail]; linux-
> > [e-mail]; [e-mail];
> > [e-mail]; [e-mail]
> > Subject: Re: [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 <[e-mail]>
> > >
> > > 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.
> >
> It's up to the caller to decide how they want it displayed.

I wonder who would want to quietly skip some data values.
Are you using it yourself? Could you please provide an
example?

I do not see why we would need to complicate the API and code
by this.

The behavior proposed by Tvrtko Ursulin makes much more
sense. I mean
https://lkml.kernel.org/r/[e-mail]


> > I wonder how it would look like when we print something like:
> > 
> >     --- skipped XX lines full of 0x00 ---
> 
> This could be added as a later enhancement, with a new flag (eg.
> HEXDUMP_SUPPRESS_VERBOSE).

Who will add this later? Frankly, this looks like a half baked
feature that it good enough for you. If you want it upstream,
it must behave reasonably and it must be worth it.

Best Regards,
Petr

Alastair D'Silva April 15, 2019, 10:33 a.m. UTC | #5

> > > On Wed 2019-04-10 13:17:18, Alastair D'Silva wrote:
> > > > From: Alastair D'Silva <[e-mail]>
> > > >
> > > > 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.
> > >
> > It's up to the caller to decide how they want it displayed.
> 
> I wonder who would want to quietly skip some data values.
> Are you using it yourself? Could you please provide an example?

Yes, but I don't have the content with me at the moment, so I can't share
it. I'm dumping persistent memory labels, which are 64kB long, but only the
first few hundred bytes are populated.
 
> I do not see why we would need to complicate the API and code by this.
> 
> The behavior proposed by Tvrtko Ursulin makes much more sense. I mean
> https://lkml.kernel.org/r/929244ed-cc7f-b0f3-b5ac-
> [e-mail]

I agree that is better, I'll add that to V2.

Patch

diff --git a/include/linux/printk.h b/include/linux/printk.h
index d7c77ed1a4cb..c014e5573665 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -479,13 +479,26 @@  enum {
 	DUMP_PREFIX_ADDRESS,
 	DUMP_PREFIX_OFFSET
 };
+
+#define HEXDUMP_ASCII		(1 << 0)
+#define HEXDUMP_SUPPRESS_0X00	(1 << 1)
+#define HEXDUMP_SUPPRESS_0XFF	(1 << 2)
+#define HEXDUMP_SUPPRESS_FIRST	(1 << 3)
+#define HEXDUMP_SUPPRESS_LAST	(1 << 4)
+
+#define HEXDUMP_QUIET		(HEXDUMP_SUPPRESS_0X00 | \
+				HEXDUMP_SUPPRESS_0XFF | \
+				HEXDUMP_SUPPRESS_FIRST | \
+				HEXDUMP_SUPPRESS_LAST)
+
 extern int hex_dump_to_buffer(const void *buf, size_t len, int rowsize,
 			      int groupsize, char *linebuf, size_t linebuflen,
 			      bool ascii);
+
 #ifdef CONFIG_PRINTK
-extern 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);
+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, u64 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)
@@ -494,18 +507,29 @@  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,
-				  int prefix_type, int rowsize, int groupsize,
-				  const void *buf, size_t len, bool ascii)
+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, u64 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 b8a164814744..2f3bafb55a44 100644
--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -209,8 +209,21 @@  int hex_dump_to_buffer(const void *buf, size_t len, int rowsize, int groupsize,
 EXPORT_SYMBOL(hex_dump_to_buffer);
 
 #ifdef CONFIG_PRINTK
+
+static bool buf_is_all(const u8 *buf, size_t len, u8 val)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++) {
+		if (buf[i] != val)
+			return false;
+	}
+
+	return true;
+}
+
 /**
- * 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
@@ -221,42 +234,73 @@  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_0X00:	suppress lines that are all 0x00
+ *				(other than first or last)
+ *	HEXDUMP_SUPPRESS_0XFF:	suppress lines that are all 0xff
+ *				(other than first or last)
+ *	HEXDUMP_SUPPRESS_FIRST:	allows the first line to be suppressed
+ *	HEXDUMP_SUPPRESS_LAST:	allows the last line to be suppressed
+ *				If the first and last line may be suppressed,
+ *				an empty buffer will not produce any output
  *
  * 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
  * leading prefix.
  *
- * print_hex_dump() works on one "line" of output at a time, i.e.,
+ * print_hex_dump_ext() works on one "line" of output at a time, i.e.,
  * 16, 32 or 64 bytes of input data converted to hex + ASCII output.
- * print_hex_dump() iterates over the entire input @buf, breaking it into
+ * print_hex_dump_ext() iterates over the entire input @buf, breaking it into
  * "line size" chunks to format and print.
  *
  * 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, 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;
+
+		first_line = false;
+
 		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);
 
 #if !defined(CONFIG_DYNAMIC_DEBUG)
 /**
@@ -290,8 +334,8 @@  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) */