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SubjectRe: [RESEND PATCH v3 1/1] lib/vsprintf: Add support for printing V4L2 and DRM fourccs
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


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