Commit 1938479b authored by Hector Martin's avatar Hector Martin Committed by Alyssa Rosenzweig
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lib/vsprintf: Add support for generic FourCCs by extending %p4cc 



%p4cc is designed for DRM/V4L2 FourCCs with their specific quirks, but
it's useful to be able to print generic 4-character codes formatted as
an integer. Extend it to add format specifiers for printing generic
32-bit FourCCs with various endian semantics:

%p4ch	Host byte order
%p4cn	Network byte order
%p4cl	Little-endian
%p4cb	Big-endian

The endianness determines how bytes are interpreted as a u32, and the
FourCC is then always printed MSByte-first (this is the opposite of
V4L/DRM FourCCs). This covers most practical cases, e.g. %p4cn would
allow printing LSByte-first FourCCs stored in host endian order
(other than the hex form being in character order, not the integer
value).

Acked-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Tested-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarHector Martin <marcan@marcan.st>
Signed-off-by: default avatarAditya Garg <gargaditya08@live.com>
Reviewed-by: default avatarKees Cook <kees@kernel.org>
Link: https://lore.kernel.org/r/PN3PR01MB9597B01823415CB7FCD3BC27B8B52@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM


Signed-off-by: default avatarAlyssa Rosenzweig <alyssa@rosenzweig.io>
parent 729f8eef

Documentation/core-api/printk-formats.rst

+32 −0
Original line number Diff line number Diff line
@@ -648,6 +648,38 @@ Examples:: 
	%p4cc	Y10  little-endian (0x20303159)

	%p4cc	NV12 big-endian (0xb231564e)



Generic FourCC code

-------------------



::

	%p4c[hnlb]	gP00 (0x67503030)



Print a generic FourCC code, as both ASCII characters and its numerical

value as hexadecimal.



The generic FourCC code is always printed in the big-endian format,

the most significant byte first. This is the opposite of V4L/DRM FourCCs.



The additional ``h``, ``n``, ``l``, and ``b`` specifiers define what

endianness is used to load the stored bytes. The data might be interpreted

using the host byte order, network byte order, little-endian, or big-endian.



Passed by reference.



Examples for a little-endian machine, given &(u32)0x67503030::



	%p4ch	gP00 (0x67503030)

	%p4cn	00Pg (0x30305067)

	%p4cl	gP00 (0x67503030)

	%p4cb	00Pg (0x30305067)



Examples for a big-endian machine, given &(u32)0x67503030::



	%p4ch	gP00 (0x67503030)

	%p4cn	00Pg (0x30305067)

	%p4cl	00Pg (0x30305067)

	%p4cb	gP00 (0x67503030)



Rust

----

lib/vsprintf.c

+29 −6
Original line number Diff line number Diff line
@@ -1793,27 +1793,50 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc, 
	char output[sizeof("0123 little-endian (0x01234567)")];

	char *p = output;

	unsigned int i;

	bool pixel_fmt = false;

	u32 orig, val;



	if (fmt[1] != 'c' || fmt[2] != 'c')

	if (fmt[1] != 'c')

		return error_string(buf, end, "(%p4?)", spec);



	if (check_pointer(&buf, end, fourcc, spec))

		return buf;



	orig = get_unaligned(fourcc);

	val = orig & ~BIT(31);

	switch (fmt[2]) {

	case 'h':

		break;

	case 'n':

		orig = swab32(orig);

		break;

	case 'l':

		orig = (__force u32)cpu_to_le32(orig);

		break;

	case 'b':

		orig = (__force u32)cpu_to_be32(orig);

		break;

	case 'c':

		/* Pixel formats are printed LSB-first */

		pixel_fmt = true;

		break;

	default:

		return error_string(buf, end, "(%p4?)", spec);

	}



	val = pixel_fmt ? swab32(orig & ~BIT(31)) : orig;



	for (i = 0; i < sizeof(u32); i++) {

		unsigned char c = val >> (i * 8);

		unsigned char c = val >> ((3 - i) * 8);



		/* Print non-control ASCII characters as-is, dot otherwise */

		*p++ = isascii(c) && isprint(c) ? c : '.';

	}



	if (pixel_fmt) {

		*p++ = ' ';

		strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");

		p += strlen(p);

	}



	*p++ = ' ';

	*p++ = '(';

scripts/checkpatch.pl

+1 −1
Original line number Diff line number Diff line
@@ -6891,7 +6891,7 @@ sub process { 
					    ($extension eq "f" &&

					     defined $qualifier && $qualifier !~ /^w/) ||

					    ($extension eq "4" &&

					     defined $qualifier && $qualifier !~ /^cc/)) {

					     defined $qualifier && $qualifier !~ /^c[hnlbc]/)) {

						$bad_specifier = $specifier;

						last;

					}