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 <mchehab@xxxxxxxxxx>
> > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > ---
> > 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
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