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
