Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
pixel formats denoted by fourccs. The fourcc encoding is the same for both
so the same implementation can be used.
Suggested-by: Mauro Carvalho Chehab <[email protected]>
Signed-off-by: Sakari Ailus <[email protected]>
---
since v2:
- Add comments to explain why things are being done
- Print characters under 32 (space) as hexadecimals in parenthesis.
- Do not print spaces in the fourcc codes.
- Make use of a loop over the fourcc characters instead of
put_unaligned_le32(). This is necessary to omit spaces in the output.
- Use DRM style format instead of V4L2. This provides the precise code as
a numerical value as well as explicit endianness information.
- Added WARN_ON_ONCE() sanity checks. Comments on these are welcome; I'd
expect them mostly be covered by the tests.
- Added tests for %p4cc in lib/test_printf.c
Documentation/core-api/printk-formats.rst | 12 ++++
lib/test_printf.c | 17 +++++
lib/vsprintf.c | 86 +++++++++++++++++++++++
3 files changed, 115 insertions(+)
diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 8ebe46b1af39..7aa0451e06fb 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -545,6 +545,18 @@ For printing netdev_features_t.
Passed by reference.
+V4L2 and DRM FourCC code (pixel format)
+---------------------------------------
+
+::
+
+ %p4cc
+
+Print a FourCC code used by V4L2 or DRM, including format endianness and
+its numerical value as hexadecimal.
+
+Passed by reference.
+
Thanks
======
diff --git a/lib/test_printf.c b/lib/test_printf.c
index 2d9f520d2f27..a14754086707 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -624,6 +624,22 @@ static void __init fwnode_pointer(void)
software_node_unregister_nodes(softnodes);
}
+static void __init fourcc_pointer(void)
+{
+ struct {
+ u32 code;
+ char *str;
+ } const try[] = {
+ { 0x20104646, "FF(10) little-endian (0x20104646)", },
+ { 0xa0104646, "FF(10) big-endian (0xa0104646)", },
+ { 0x10111213, "(13)(12)(11)(10) little-endian (0x10111213)", },
+ };
+ unsigned int i;
+
+ for (i = 0; i < ARRAY_SIZE(try); i++)
+ test(try[i].str, "%p4cc", &try[i].code);
+}
+
static void __init
errptr(void)
{
@@ -668,6 +684,7 @@ test_pointer(void)
flags();
errptr();
fwnode_pointer();
+ fourcc_pointer();
}
static void __init selftest(void)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 7c488a1ce318..02e7906619c0 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1721,6 +1721,89 @@ char *netdev_bits(char *buf, char *end, const void *addr,
return special_hex_number(buf, end, num, size);
}
+static noinline_for_stack
+char *fourcc_string(char *buf, char *end, const u32 *__fourcc,
+ struct printf_spec spec, const char *fmt)
+{
+#define FOURCC_HEX_CHAR_STR "(xx)"
+#define FOURCC_BIG_ENDIAN_STR " big-endian"
+#define FOURCC_LITTLE_ENDIAN_STR " little-endian"
+#define FOURCC_HEX_NUMBER " (0x01234567)"
+#define FOURCC_STRING_MAX \
+ FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR \
+ FOURCC_HEX_CHAR_STR FOURCC_LITTLE_ENDIAN_STR FOURCC_HEX_NUMBER
+ struct printf_spec my_spec = {
+ .type = FORMAT_TYPE_UINT,
+ .field_width = 2,
+ .flags = SMALL,
+ .base = 16,
+ .precision = -1,
+ };
+ char __s[sizeof(FOURCC_STRING_MAX)];
+ char *s = __s;
+ unsigned int i;
+ /*
+ * The 31st bit defines the endianness of the data, so save its printing
+ * for later.
+ */
+ u32 fourcc = *__fourcc & ~BIT(31);
+ int ret;
+
+ if (check_pointer(&buf, end, __fourcc, spec))
+ return buf;
+
+ if (fmt[1] != 'c' || fmt[2] != 'c')
+ return error_string(buf, end, "(%p4?)", spec);
+
+ for (i = 0; i < sizeof(fourcc); i++, fourcc >>= 8) {
+ unsigned char c = fourcc;
+
+ /* Weed out spaces */
+ if (c == ' ')
+ continue;
+
+ /* Print non-control characters as-is */
+ if (c > ' ') {
+ *s = c;
+ s++;
+ continue;
+ }
+
+ if (WARN_ON_ONCE(sizeof(__s) <
+ (s - __s) + sizeof(FOURCC_HEX_CHAR_STR)))
+ break;
+
+ *s = '(';
+ s++;
+ s = number(s, s + 2, c, my_spec);
+ *s = ')';
+ s++;
+ }
+
+ ret = strscpy(s, *__fourcc & BIT(31) ? FOURCC_BIG_ENDIAN_STR
+ : FOURCC_LITTLE_ENDIAN_STR,
+ sizeof(__s) - (s - __s));
+ if (!WARN_ON_ONCE(ret < 0))
+ s += ret;
+
+ if (!WARN_ON_ONCE(sizeof(__s) <
+ (s - __s) + sizeof(FOURCC_HEX_NUMBER))) {
+ *s = ' ';
+ s++;
+ *s = '(';
+ s++;
+ /* subtract parentheses and the space from the size */
+ special_hex_number(s, s + sizeof(FOURCC_HEX_NUMBER) - 3,
+ *__fourcc, sizeof(u32));
+ s += sizeof(u32) * 2 + 2 /* 0x */;
+ *s = ')';
+ s++;
+ *s = '\0';
+ }
+
+ return string(buf, end, __s, spec);
+}
+
static noinline_for_stack
char *address_val(char *buf, char *end, const void *addr,
struct printf_spec spec, const char *fmt)
@@ -2131,6 +2214,7 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
* correctness of the format string and va_list arguments.
* - 'K' For a kernel pointer that should be hidden from unprivileged users
* - 'NF' For a netdev_features_t
+ * - '4cc' V4L2 or DRM FourCC code, with endianness and raw numerical value.
* - 'h[CDN]' For a variable-length buffer, it prints it as a hex string with
* a certain separator (' ' by default):
* C colon
@@ -2223,6 +2307,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
return restricted_pointer(buf, end, ptr, spec);
case 'N':
return netdev_bits(buf, end, ptr, spec, fmt);
+ case '4':
+ return fourcc_string(buf, end, ptr, spec, fmt);
case 'a':
return address_val(buf, end, ptr, spec, fmt);
case 'd':
--
2.20.1
On Mon, Apr 27, 2020 at 05:53:03PM +0300, Sakari Ailus wrote:
> Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
> pixel formats denoted by fourccs. The fourcc encoding is the same for both
> so the same implementation can be used.
4cc is more generic than pixel format.
...
> +V4L2 and DRM FourCC code (pixel format)
> +---------------------------------------
> +
> +::
> +
> + %p4cc
Missed examples.
> +Print a FourCC code used by V4L2 or DRM, including format endianness and
> +its numerical value as hexadecimal.
...
> +static noinline_for_stack
> +char *fourcc_string(char *buf, char *end, const u32 *__fourcc,
> + struct printf_spec spec, const char *fmt)
> +{
> +#define FOURCC_HEX_CHAR_STR "(xx)"
> +#define FOURCC_BIG_ENDIAN_STR " big-endian"
> +#define FOURCC_LITTLE_ENDIAN_STR " little-endian"
> +#define FOURCC_HEX_NUMBER " (0x01234567)"
Where are #undef:s?
> +#define FOURCC_STRING_MAX \
> + FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR \
> + FOURCC_HEX_CHAR_STR FOURCC_LITTLE_ENDIAN_STR FOURCC_HEX_NUMBER
> + struct printf_spec my_spec = {
> + .type = FORMAT_TYPE_UINT,
> + .field_width = 2,
> + .flags = SMALL,
> + .base = 16,
> + .precision = -1,
> + };
Seems like close enough to bus_spec.
> + char __s[sizeof(FOURCC_STRING_MAX)];
> + char *s = __s;
> + unsigned int i;
> + /*
> + * The 31st bit defines the endianness of the data, so save its printing
> + * for later.
> + */
> + u32 fourcc = *__fourcc & ~BIT(31);
> + int ret;
> +
> + if (check_pointer(&buf, end, __fourcc, spec))
> + return buf;
> +
> + if (fmt[1] != 'c' || fmt[2] != 'c')
> + return error_string(buf, end, "(%p4?)", spec);
> +
> + for (i = 0; i < sizeof(fourcc); i++, fourcc >>= 8) {
> + unsigned char c = fourcc;
> +
> + /* Weed out spaces */
> + if (c == ' ')
> + continue;
> +
> + /* Print non-control characters as-is */
> + if (c > ' ') {
> + *s = c;
> + s++;
> + continue;
> + }
> + if (WARN_ON_ONCE(sizeof(__s) <
> + (s - __s) + sizeof(FOURCC_HEX_CHAR_STR)))
Why WARN?!
> + break;
> +
> + *s = '(';
> + s++;
> + s = number(s, s + 2, c, my_spec);
> + *s = ')';
> + s++;
> + }
> +
> + ret = strscpy(s, *__fourcc & BIT(31) ? FOURCC_BIG_ENDIAN_STR
> + : FOURCC_LITTLE_ENDIAN_STR,
> + sizeof(__s) - (s - __s));
> + if (!WARN_ON_ONCE(ret < 0))
Ditto.
> + s += ret;
> + if (!WARN_ON_ONCE(sizeof(__s) <
> + (s - __s) + sizeof(FOURCC_HEX_NUMBER))) {
Ditto.
> + *s = ' ';
> + s++;
> + *s = '(';
> + s++;
> + /* subtract parentheses and the space from the size */
> + special_hex_number(s, s + sizeof(FOURCC_HEX_NUMBER) - 3,
> + *__fourcc, sizeof(u32));
> + s += sizeof(u32) * 2 + 2 /* 0x */;
> + *s = ')';
> + s++;
> + *s = '\0';
> + }
> +
> + return string(buf, end, __s, spec);
This looks overengineered. Why everyone will need so long strings to be printed?
> +}
--
With Best Regards,
Andy Shevchenko
On 27/04/2020 16.53, Sakari Ailus wrote:
> Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
> pixel formats denoted by fourccs. The fourcc encoding is the same for both
> so the same implementation can be used.
>
> Suggested-by: Mauro Carvalho Chehab <[email protected]>
> Signed-off-by: Sakari Ailus <[email protected]>
> ---
> since v2:
>
> - Add comments to explain why things are being done
>
> - Print characters under 32 (space) as hexadecimals in parenthesis.
>
> - Do not print spaces in the fourcc codes.
>
> - Make use of a loop over the fourcc characters instead of
> put_unaligned_le32(). This is necessary to omit spaces in the output.
>
> - Use DRM style format instead of V4L2. This provides the precise code as
> a numerical value as well as explicit endianness information.
>
> - Added WARN_ON_ONCE() sanity checks. Comments on these are welcome; I'd
> expect them mostly be covered by the tests.
>
> - Added tests for %p4cc in lib/test_printf.c
>
> Documentation/core-api/printk-formats.rst | 12 ++++
> lib/test_printf.c | 17 +++++
> lib/vsprintf.c | 86 +++++++++++++++++++++++
> 3 files changed, 115 insertions(+)
>
> diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> index 8ebe46b1af39..7aa0451e06fb 100644
> --- a/Documentation/core-api/printk-formats.rst
> +++ b/Documentation/core-api/printk-formats.rst
> @@ -545,6 +545,18 @@ For printing netdev_features_t.
>
> Passed by reference.
>
> +V4L2 and DRM FourCC code (pixel format)
> +---------------------------------------
> +
> +::
> +
> + %p4cc
> +
> +Print a FourCC code used by V4L2 or DRM, including format endianness and
> +its numerical value as hexadecimal.
> +
> +Passed by reference.
> +
> Thanks
> ======
>
> diff --git a/lib/test_printf.c b/lib/test_printf.c
> index 2d9f520d2f27..a14754086707 100644
> --- a/lib/test_printf.c
> +++ b/lib/test_printf.c
> @@ -624,6 +624,22 @@ static void __init fwnode_pointer(void)
> software_node_unregister_nodes(softnodes);
> }
>
> +static void __init fourcc_pointer(void)
> +{
> + struct {
> + u32 code;
> + char *str;
> + } const try[] = {
> + { 0x20104646, "FF(10) little-endian (0x20104646)", },
> + { 0xa0104646, "FF(10) big-endian (0xa0104646)", },
> + { 0x10111213, "(13)(12)(11)(10) little-endian (0x10111213)", },
> + };
> + unsigned int i;
> +
> + for (i = 0; i < ARRAY_SIZE(try); i++)
> + test(try[i].str, "%p4cc", &try[i].code);
> +}
> +
> static void __init
> errptr(void)
> {
> @@ -668,6 +684,7 @@ test_pointer(void)
> flags();
> errptr();
> fwnode_pointer();
> + fourcc_pointer();
> }
>
> static void __init selftest(void)
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 7c488a1ce318..02e7906619c0 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1721,6 +1721,89 @@ char *netdev_bits(char *buf, char *end, const void *addr,
> return special_hex_number(buf, end, num, size);
> }
>
> +static noinline_for_stack
> +char *fourcc_string(char *buf, char *end, const u32 *__fourcc,
> + struct printf_spec spec, const char *fmt)
> +{
> +#define FOURCC_HEX_CHAR_STR "(xx)"
> +#define FOURCC_BIG_ENDIAN_STR " big-endian"
> +#define FOURCC_LITTLE_ENDIAN_STR " little-endian"
> +#define FOURCC_HEX_NUMBER " (0x01234567)"
> +#define FOURCC_STRING_MAX \
> + FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR \
> + FOURCC_HEX_CHAR_STR FOURCC_LITTLE_ENDIAN_STR FOURCC_HEX_NUMBER
> + struct printf_spec my_spec = {
> + .type = FORMAT_TYPE_UINT,
> + .field_width = 2,
> + .flags = SMALL,
> + .base = 16,
> + .precision = -1,
> + };
> + char __s[sizeof(FOURCC_STRING_MAX)];
> + char *s = __s;
> + unsigned int i;
> + /*
> + * The 31st bit defines the endianness of the data, so save its printing
> + * for later.
> + */
> + u32 fourcc = *__fourcc & ~BIT(31);
> + int ret;
Dereference __fourcc ...
> + if (check_pointer(&buf, end, __fourcc, spec))
> + return buf;
.. and then sanity check it?
> + if (fmt[1] != 'c' || fmt[2] != 'c')
> + return error_string(buf, end, "(%p4?)", spec);
Doesn't that want to come before everything else, including the
check_pointer()?
> + for (i = 0; i < sizeof(fourcc); i++, fourcc >>= 8) {
> + unsigned char c = fourcc;
> +
> + /* Weed out spaces */
> + if (c == ' ')
> + continue;
> +
> + /* Print non-control characters as-is */
> + if (c > ' ') {
> + *s = c;
> + s++;
> + continue;
> + }
Are you sure you want to pass non-ascii characters through?
> + if (WARN_ON_ONCE(sizeof(__s) <
> + (s - __s) + sizeof(FOURCC_HEX_CHAR_STR)))
> + break;
I really don't see the point of these checks. Why check here but not
before we output a non-control character? That seems rather arbitrary.
Also, assume we do take this break, (to be continued below [*])
> + *s = '(';
> + s++;
> + s = number(s, s + 2, c, my_spec);
You can drop my_spec and just use "s = hex_byte_pack(s, c);".
> + *s = ')';
> + s++;
> + }
> +
> + ret = strscpy(s, *__fourcc & BIT(31) ? FOURCC_BIG_ENDIAN_STR
> + : FOURCC_LITTLE_ENDIAN_STR,
> + sizeof(__s) - (s - __s));
> + if (!WARN_ON_ONCE(ret < 0))
> + s += ret;
> +
> + if (!WARN_ON_ONCE(sizeof(__s) <
> + (s - __s) + sizeof(FOURCC_HEX_NUMBER))) {
[*] then AFAICT this WARN_ON_ONCE is guaranteed to also fire [the
left-hand side is the same as before, the right-hand side consists of a
quantity s-__s that can only be larger or equal than before and a
constant sizeof(FOURCC_HEX_NUMBER) that is definitely larger], hence we
do not enter this if () and [**]
> + *s = ' ';
> + s++;
> + *s = '(';
> + s++;
> + /* subtract parentheses and the space from the size */
> + special_hex_number(s, s + sizeof(FOURCC_HEX_NUMBER) - 3,
> + *__fourcc, sizeof(u32));
Urgh. Don't we have an ARRAY_END() macro that let's you call this with
(s, ARRAY_END(__s)) as buf, end?
> + s += sizeof(u32) * 2 + 2 /* 0x */;
Why, when special_hex_number returns a pointer to one-past-its-output?
> + *s = ')';
> + s++;
> + *s = '\0';
> + }
> +
> + return string(buf, end, __s, spec);
[**] __s does not get nul-terminated, so we call string() with stack
garbage.
I'd say just drop those checks, and de-obfuscate the sizing of the __s
array so it becomes obviously large enough for what the algorithm can
produce. Just
char __s[sizeof("(01)(02)(03)(04) little-endian (0x01020304)")]
or something like that should be sufficient.
Rasmus
On Mon, 2020-04-27 at 17:53 +0300, Sakari Ailus wrote:
> Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
> pixel formats denoted by fourccs. The fourcc encoding is the same for both
> so the same implementation can be used.
[]
> - Added WARN_ON_ONCE() sanity checks. Comments on these are welcome; I'd
> expect them mostly be covered by the tests.
All the WARN_ON_ONCE uses are not necessary.
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
[]
> @@ -1721,6 +1721,89 @@ char *netdev_bits(char *buf, char *end, const void *addr,
> return special_hex_number(buf, end, num, size);
> }
>
> +static noinline_for_stack
> +char *fourcc_string(char *buf, char *end, const u32 *__fourcc,
> + struct printf_spec spec, const char *fmt)
There's no reason to use __ prefixed argument names here.
> +{
> +#define FOURCC_HEX_CHAR_STR "(xx)"
> +#define FOURCC_BIG_ENDIAN_STR " big-endian"
> +#define FOURCC_LITTLE_ENDIAN_STR " little-endian"
I don't believe used-once macro defines are useful.
> +#define FOURCC_HEX_NUMBER " (0x01234567)"
> +#define FOURCC_STRING_MAX \
> + FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR \
> + FOURCC_HEX_CHAR_STR FOURCC_LITTLE_ENDIAN_STR FOURCC_HEX_NUMBER
This is very difficult to read and is size dependent on
the size of little-endian > big_endian
I'd write it out
FOURCC_STRING_MAX sizeof("(xx)(xx)(xx)(xx) little-endian (0x01234567)")
and then not have the define at all but use
the written out string in the declaration.
> + struct printf_spec my_spec = {
> + .type = FORMAT_TYPE_UINT,
> + .field_width = 2,
> + .flags = SMALL,
> + .base = 16,
> + .precision = -1,
> + };
my_spec isn't usefully named, likely not necessary at all,
and if really necessary, it should be static const
> + char __s[sizeof(FOURCC_STRING_MAX)];
I'd declare the buffer
char fourcc[sizeof("(xx)(xx)(xx)(xx) little-endian (0x01234567)"];
like all the other specialty functions do.
> + char *s = __s;
There's no reason to use __ prefixed variable names here either.
All the other specialty function use:
char *p = <output_buffer_name>;
> + unsigned int i;
just int i; is typical
> + /*
> + * The 31st bit defines the endianness of the data, so save its printing
> + * for later.
> + */
> + u32 fourcc = *__fourcc & ~BIT(31);
bool be = fourcc & BIT(31);
> + int ret;
> +
> + if (check_pointer(&buf, end, __fourcc, spec))
> + return buf;
> +
> + if (fmt[1] != 'c' || fmt[2] != 'c')
> + return error_string(buf, end, "(%p4?)", spec);
> +
> + for (i = 0; i < sizeof(fourcc); i++, fourcc >>= 8) {
> + unsigned char c = fourcc >> (i*8);
Please remove the fourcc >>= 8 from the loop and use
unsigned char c = fourcc >> (i*8);
If I understand this correctly, I think this is simpler:
if (isascii(c) && isprint(c)) {
*s++ = c;
} else {
*s++ = '(';
s = hex_byte_pack(s, c);
*s++ = ')';
}
> +
> + /* Weed out spaces */
> + if (c == ' ')
> + continue;
> +
> + /* Print non-control characters as-is */
> + if (c > ' ') {
> + *s = c;
> + s++;
> + continue;
> + }
> +
> + if (WARN_ON_ONCE(sizeof(__s) <
> + (s - __s) + sizeof(FOURCC_HEX_CHAR_STR)))
> + break;
> +
> + *s = '(';
> + s++;
> + s = number(s, s + 2, c, my_spec);
> + *s = ')';
> + s++;
> + }
> +
> + ret = strscpy(s, *__fourcc & BIT(31) ? FOURCC_BIG_ENDIAN_STR
> + : FOURCC_LITTLE_ENDIAN_STR,
> + sizeof(__s) - (s - __s));
If you size the initial buffer correctly, strscpy is unnecessary.
strcpy(s, <bit31> ? "big endian" : "little endian");
s += strlen(s);
> + if (!WARN_ON_ONCE(ret < 0))
> + s += ret;
> +
> + if (!WARN_ON_ONCE(sizeof(__s) <
> + (s - __s) + sizeof(FOURCC_HEX_NUMBER))) {
> + *s = ' ';
> + s++;
> + *s = '(';
> + s++;
*s++ = ' ';
*s++ = '(';
+ /* subtract parentheses and the space from the size */
> + special_hex_number(s, s + sizeof(FOURCC_HEX_NUMBER) - 3,
> + *__fourcc, sizeof(u32));
> + s += sizeof(u32) * 2 + 2 /* 0x */;
> + *s = ')';
> + s++;
*s++ = ')';
> + *s = '\0';
> + }
> +
> + return string(buf, end, __s, spec);
> +}
>
On Mon, 2020-04-27 at 09:02 -0700, Joe Perches wrote:
> On Mon, 2020-04-27 at 17:53 +0300, Sakari Ailus wrote:
> > Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
> > pixel formats denoted by fourccs. The fourcc encoding is the same for both
> > so the same implementation can be used.
> []
> > - Added WARN_ON_ONCE() sanity checks. Comments on these are welcome; I'd
> > expect them mostly be covered by the tests.
perhaps this is simpler?
---
lib/vsprintf.c | 43 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 43 insertions(+)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 7c488a..3e1dbd7 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1721,6 +1721,46 @@ char *netdev_bits(char *buf, char *end, const void *addr,
return special_hex_number(buf, end, num, size);
}
+static noinline_for_stack
+char *fourcc_string(char *buf, char *end, const u32 *fourcc,
+ struct printf_spec spec, const char *fmt)
+{
+ char output[sizeof("(xx)(xx)(xx)(xx) little-endian (0x01234567)")];
+ char *p = output;
+ int i;
+ u32 val;
+
+ if (check_pointer(&buf, end, fourcc, spec))
+ return buf;
+
+ if (fmt[1] != 'c' || fmt[2] != 'c')
+ return error_string(buf, end, "(%p4?)", spec);
+
+ val = *fourcc & ~BIT(31);
+
+ for (i = 0; i < 4; i++) {
+ unsigned char c = val >> (i * 8);
+
+ if (isascii(c) && isprint(c)) {
+ *p++ = c;
+ } else {
+ *p++ = '(';
+ p = hex_byte_pack(p, c);
+ *p++ = ')';
+ }
+ }
+
+ strcpy(p, *fourcc & BIT(31) ? "big endian" : "little endian");
+ p += strlen(p);
+ *p++ = ' ';
+ *p++ = '(';
+ p = special_hex_number(p, p + 10, val, 4);
+ *p++ = ')';
+ *p = 0;
+
+ return string(buf, end, output, spec);
+}
+
static noinline_for_stack
char *address_val(char *buf, char *end, const void *addr,
struct printf_spec spec, const char *fmt)
@@ -2131,6 +2171,7 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
* correctness of the format string and va_list arguments.
* - 'K' For a kernel pointer that should be hidden from unprivileged users
* - 'NF' For a netdev_features_t
+ * - '4cc' V4L2 or DRM FourCC code, with endianness and raw numerical value.
* - 'h[CDN]' For a variable-length buffer, it prints it as a hex string with
* a certain separator (' ' by default):
* C colon
@@ -2223,6 +2264,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
return restricted_pointer(buf, end, ptr, spec);
case 'N':
return netdev_bits(buf, end, ptr, spec, fmt);
+ case '4':
+ return fourcc_string(buf, end, ptr, spec, fmt);
case 'a':
return address_val(buf, end, ptr, spec, fmt);
case 'd':
Hi Rasmus,
Thanks for the review.
On Mon, Apr 27, 2020 at 05:44:00PM +0200, Rasmus Villemoes wrote:
> On 27/04/2020 16.53, Sakari Ailus wrote:
> > Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
> > pixel formats denoted by fourccs. The fourcc encoding is the same for both
> > so the same implementation can be used.
> >
> > Suggested-by: Mauro Carvalho Chehab <[email protected]>
> > Signed-off-by: Sakari Ailus <[email protected]>
> > ---
> > since v2:
> >
> > - Add comments to explain why things are being done
> >
> > - Print characters under 32 (space) as hexadecimals in parenthesis.
> >
> > - Do not print spaces in the fourcc codes.
> >
> > - Make use of a loop over the fourcc characters instead of
> > put_unaligned_le32(). This is necessary to omit spaces in the output.
> >
> > - Use DRM style format instead of V4L2. This provides the precise code as
> > a numerical value as well as explicit endianness information.
> >
> > - Added WARN_ON_ONCE() sanity checks. Comments on these are welcome; I'd
> > expect them mostly be covered by the tests.
> >
> > - Added tests for %p4cc in lib/test_printf.c
> >
> > Documentation/core-api/printk-formats.rst | 12 ++++
> > lib/test_printf.c | 17 +++++
> > lib/vsprintf.c | 86 +++++++++++++++++++++++
> > 3 files changed, 115 insertions(+)
> >
> > diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> > index 8ebe46b1af39..7aa0451e06fb 100644
> > --- a/Documentation/core-api/printk-formats.rst
> > +++ b/Documentation/core-api/printk-formats.rst
> > @@ -545,6 +545,18 @@ For printing netdev_features_t.
> >
> > Passed by reference.
> >
> > +V4L2 and DRM FourCC code (pixel format)
> > +---------------------------------------
> > +
> > +::
> > +
> > + %p4cc
> > +
> > +Print a FourCC code used by V4L2 or DRM, including format endianness and
> > +its numerical value as hexadecimal.
> > +
> > +Passed by reference.
> > +
> > Thanks
> > ======
> >
> > diff --git a/lib/test_printf.c b/lib/test_printf.c
> > index 2d9f520d2f27..a14754086707 100644
> > --- a/lib/test_printf.c
> > +++ b/lib/test_printf.c
> > @@ -624,6 +624,22 @@ static void __init fwnode_pointer(void)
> > software_node_unregister_nodes(softnodes);
> > }
> >
> > +static void __init fourcc_pointer(void)
> > +{
> > + struct {
> > + u32 code;
> > + char *str;
> > + } const try[] = {
> > + { 0x20104646, "FF(10) little-endian (0x20104646)", },
> > + { 0xa0104646, "FF(10) big-endian (0xa0104646)", },
> > + { 0x10111213, "(13)(12)(11)(10) little-endian (0x10111213)", },
> > + };
> > + unsigned int i;
> > +
> > + for (i = 0; i < ARRAY_SIZE(try); i++)
> > + test(try[i].str, "%p4cc", &try[i].code);
> > +}
> > +
> > static void __init
> > errptr(void)
> > {
> > @@ -668,6 +684,7 @@ test_pointer(void)
> > flags();
> > errptr();
> > fwnode_pointer();
> > + fourcc_pointer();
> > }
> >
> > static void __init selftest(void)
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index 7c488a1ce318..02e7906619c0 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -1721,6 +1721,89 @@ char *netdev_bits(char *buf, char *end, const void *addr,
> > return special_hex_number(buf, end, num, size);
> > }
> >
> > +static noinline_for_stack
> > +char *fourcc_string(char *buf, char *end, const u32 *__fourcc,
> > + struct printf_spec spec, const char *fmt)
> > +{
> > +#define FOURCC_HEX_CHAR_STR "(xx)"
> > +#define FOURCC_BIG_ENDIAN_STR " big-endian"
> > +#define FOURCC_LITTLE_ENDIAN_STR " little-endian"
> > +#define FOURCC_HEX_NUMBER " (0x01234567)"
> > +#define FOURCC_STRING_MAX \
> > + FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR FOURCC_HEX_CHAR_STR \
> > + FOURCC_HEX_CHAR_STR FOURCC_LITTLE_ENDIAN_STR FOURCC_HEX_NUMBER
> > + struct printf_spec my_spec = {
> > + .type = FORMAT_TYPE_UINT,
> > + .field_width = 2,
> > + .flags = SMALL,
> > + .base = 16,
> > + .precision = -1,
> > + };
> > + char __s[sizeof(FOURCC_STRING_MAX)];
> > + char *s = __s;
> > + unsigned int i;
> > + /*
> > + * The 31st bit defines the endianness of the data, so save its printing
> > + * for later.
> > + */
> > + u32 fourcc = *__fourcc & ~BIT(31);
> > + int ret;
>
> Dereference __fourcc ...
>
> > + if (check_pointer(&buf, end, __fourcc, spec))
> > + return buf;
>
> .. and then sanity check it?
>
> > + if (fmt[1] != 'c' || fmt[2] != 'c')
> > + return error_string(buf, end, "(%p4?)", spec);
>
> Doesn't that want to come before everything else, including the
> check_pointer()?
Agreed on all three.
>
> > + for (i = 0; i < sizeof(fourcc); i++, fourcc >>= 8) {
> > + unsigned char c = fourcc;
> > +
> > + /* Weed out spaces */
> > + if (c == ' ')
> > + continue;
> > +
> > + /* Print non-control characters as-is */
> > + if (c > ' ') {
> > + *s = c;
> > + s++;
> > + continue;
> > + }
>
> Are you sure you want to pass non-ascii characters through?
I'll print the hexadecimal value in v4.
>
> > + if (WARN_ON_ONCE(sizeof(__s) <
> > + (s - __s) + sizeof(FOURCC_HEX_CHAR_STR)))
> > + break;
>
> I really don't see the point of these checks. Why check here but not
> before we output a non-control character? That seems rather arbitrary.
> Also, assume we do take this break, (to be continued below [*])
Will remove.
>
> > + *s = '(';
> > + s++;
> > + s = number(s, s + 2, c, my_spec);
>
> You can drop my_spec and just use "s = hex_byte_pack(s, c);".
Ack, this cleans it up indeed.
>
> > + *s = ')';
> > + s++;
> > + }
> > +
> > + ret = strscpy(s, *__fourcc & BIT(31) ? FOURCC_BIG_ENDIAN_STR
> > + : FOURCC_LITTLE_ENDIAN_STR,
> > + sizeof(__s) - (s - __s));
> > + if (!WARN_ON_ONCE(ret < 0))
> > + s += ret;
> > +
> > + if (!WARN_ON_ONCE(sizeof(__s) <
> > + (s - __s) + sizeof(FOURCC_HEX_NUMBER))) {
>
> [*] then AFAICT this WARN_ON_ONCE is guaranteed to also fire [the
> left-hand side is the same as before, the right-hand side consists of a
> quantity s-__s that can only be larger or equal than before and a
> constant sizeof(FOURCC_HEX_NUMBER) that is definitely larger], hence we
> do not enter this if () and [**]
>
> > + *s = ' ';
> > + s++;
> > + *s = '(';
> > + s++;
> > + /* subtract parentheses and the space from the size */
> > + special_hex_number(s, s + sizeof(FOURCC_HEX_NUMBER) - 3,
> > + *__fourcc, sizeof(u32));
>
> Urgh. Don't we have an ARRAY_END() macro that let's you call this with
> (s, ARRAY_END(__s)) as buf, end?
We do, yes. In drivers/block/floppy.c. :-)
>
> > + s += sizeof(u32) * 2 + 2 /* 0x */;
>
> Why, when special_hex_number returns a pointer to one-past-its-output?
I'll use that for v4.
>
> > + *s = ')';
> > + s++;
> > + *s = '\0';
> > + }
> > +
> > + return string(buf, end, __s, spec);
>
> [**] __s does not get nul-terminated, so we call string() with stack
> garbage.
>
> I'd say just drop those checks, and de-obfuscate the sizing of the __s
> array so it becomes obviously large enough for what the algorithm can
> produce. Just
>
> char __s[sizeof("(01)(02)(03)(04) little-endian (0x01020304)")]
>
> or something like that should be sufficient.
Done.
--
Kind regards,
Sakari Ailus