| Message ID | 20201103133400.24805-1-sakari.ailus@linux.intel.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v4,1/1] lib/vsprintf: Add support for printing V4L2 and DRM fourccs | expand |
On Tue, Nov 03, 2020 at 03:34:00PM +0200, 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. ... > +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)")]; I would add a comment that there is another possibility, i.e. big-endian, but it occupies less space. > + char *p = output; > + unsigned int i; > + u32 val; > + > + if (fmt[1] != 'c' || fmt[2] != 'c') > + return error_string(output, end, "(%p4?)", spec); > + > + if (check_pointer(&buf, end, fourcc, spec)) > + return buf; > + > + val = *fourcc & ~BIT(31); > + > + for (i = 0; i < sizeof(*fourcc); i++) { > + unsigned char c = val >> (i * 8); > + > + /* Weed out spaces */ > + if (c == ' ') > + continue; > + > + /* Print non-control ASCII characters as-is */ > + if (isascii(c) && isprint(c)) { > + *p++ = c; > + continue; > + } > + > + *p++ = '('; > + p = hex_byte_pack(p, c); > + *p++ = ')'; > + } I guess above loop can be still optimized, but I have to think about it. > + strcpy(p, *fourcc & BIT(31) ? " big-endian" : " little-endian"); > + p += strlen(p); > + > + *p++ = ' '; > + *p++ = '('; > + /* subtract parenthesis and the space from the size */ This comment misleading. What you are subtracting is a room for closing parenthesis and NUL. > + p = special_hex_number(p, output + sizeof(output) - 2, *fourcc, > + sizeof(u32)); I would go with one line here. The (theoretical) problem is here that the case when buffer size is not enough to print a value will be like '(0xabc)' but should be rather '(0xabcd' like snprintf() does in general. > + *p++ = ')'; > + *p = '\0'; > + > + return string(buf, end, output, spec); > +} -- With Best Regards, Andy Shevchenko
On Tue, Nov 03, 2020 at 04:56:16PM +0200, Sakari Ailus wrote: > On Tue, Nov 03, 2020 at 04:47:47PM +0200, Andy Shevchenko wrote: > > On Tue, Nov 03, 2020 at 03:34:00PM +0200, 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. ... > > > + char output[sizeof("(xx)(xx)(xx)(xx) little-endian (0x01234567)")]; > > > > I would add a comment that there is another possibility, i.e. big-endian, but > > it occupies less space. > > This string is here to represent the longest possible output of the > function. Most of the time it's less. Saying that might make sense but it's > fairly clear already. Either way works for me though. It's not known by reading the above line. I would add a comment. ... > > > + p = special_hex_number(p, output + sizeof(output) - 2, *fourcc, > > > + sizeof(u32)); > > > > I would go with one line here. > > It's wrapped since the result would be over 80 otherwise. It will be not the first one breaking the limit in this module for the sake of readability. ... > > The (theoretical) problem is here that the case when buffer size is not enough > > to print a value will be like '(0xabc)' but should be rather '(0xabcd' like > > snprintf() does in general. Any comments here? Perhaps you need to add a comment to explain that the overflow is impossible. -- With Best Regards, Andy Shevchenko
On Fri, 2020-11-13 at 12:54 +0200, Sakari Ailus wrote: > Hi Joe, > > On Tue, Nov 03, 2020 at 08:49:36AM -0800, Joe Perches wrote: > > On Tue, 2020-11-03 at 16:56 +0200, Sakari Ailus wrote: > > > On Tue, Nov 03, 2020 at 04:47:47PM +0200, Andy Shevchenko wrote: > > > > On Tue, Nov 03, 2020 at 03:34:00PM +0200, 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. > > > > > > > > ... > > > > > > > > > +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)")]; > > > > > > > > I would add a comment that there is another possibility, i.e. big-endian, but > > > > it occupies less space. > > > > I think it's unnecessary as it's obvious and similarly done in other > > <foo>_string type functions. > > > > > > > + p = special_hex_number(p, output + sizeof(output) - 2, *fourcc, > > > > > + sizeof(u32)); > > > > > > > > I would go with one line here. > > > > > > It's wrapped since the result would be over 80 otherwise. > > > > Perhaps simpler as > > > > p = special_hex_number(p, p + 10, *fourcc, sizeof(u32)); > > Yes. But having bugs elsewhere would have a magnified effect. How's that? Where would "elsewhere" be? > I wouldn't be afraid of a newline here. I'd prefer obvious code instead of indirected p vs output and having to lookup whatever output is again. special_hex_number is already known to fit in the buffer.
diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst index 6d26c5c6ac48..080262d2e030 100644 --- a/Documentation/core-api/printk-formats.rst +++ b/Documentation/core-api/printk-formats.rst @@ -565,6 +565,22 @@ 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. + +Examples:: + + %p4cc BG12 little-endian (0x32314742) + Thanks ====== diff --git a/lib/test_printf.c b/lib/test_printf.c index 7ac87f18a10f..7fb042542660 100644 --- a/lib/test_printf.c +++ b/lib/test_printf.c @@ -649,6 +649,22 @@ static void __init fwnode_pointer(void) software_node_unregister(&softnodes[0]); } +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) { @@ -694,6 +710,7 @@ 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 14c9a6af1b23..2be86b302c88 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1733,6 +1733,55 @@ 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; + unsigned int i; + u32 val; + + if (fmt[1] != 'c' || fmt[2] != 'c') + return error_string(output, end, "(%p4?)", spec); + + if (check_pointer(&buf, end, fourcc, spec)) + return buf; + + val = *fourcc & ~BIT(31); + + for (i = 0; i < sizeof(*fourcc); i++) { + unsigned char c = val >> (i * 8); + + /* Weed out spaces */ + if (c == ' ') + continue; + + /* Print non-control ASCII characters as-is */ + if (isascii(c) && isprint(c)) { + *p++ = c; + continue; + } + + *p++ = '('; + p = hex_byte_pack(p, c); + *p++ = ')'; + } + + strcpy(p, *fourcc & BIT(31) ? " big-endian" : " little-endian"); + p += strlen(p); + + *p++ = ' '; + *p++ = '('; + /* subtract parenthesis and the space from the size */ + p = special_hex_number(p, output + sizeof(output) - 2, *fourcc, + sizeof(u32)); + *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) @@ -2162,6 +2211,7 @@ 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 @@ -2259,6 +2309,8 @@ 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':
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@kernel.org> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com> --- Hi folks, I believe I've addressed comments from Rasmus, Joe and Andy --- variables that don't need to be negative have remained unsigned though. Thanks for the suggestions, I believe this is much cleaner than v3. since v3: - Remove use of WARN_ON, assume the code is correct instead. A side effect of this is the code is much easier to understand. - Check the modifier first before validating the buf pointer. - Use isascii() and isprint() functions to weed out non-printable characters. - Use hex_byte_pack() for printing 8-bit hexadecimal numbers. - Remove macros, and instead use plain strings. - Use strcpy() to copy the endianness string, and then strlen() to add its length. - Strip the MSB (endianness bit), then use the value as such. - Assign characters to the buffer and increment active pointer at the same time. - Drop __ from variable names. - Add example to documentation. Documentation/core-api/printk-formats.rst | 16 +++++++ lib/test_printf.c | 17 ++++++++ lib/vsprintf.c | 52 +++++++++++++++++++++++ 3 files changed, 85 insertions(+)