[OpenWrt-Devel] [RFC] libubox/binary.h design proposal

[Javier Domingo Cansino]

After feedback in IRC, I will drop this idea, and try to go the kernel way,
supporting endianess annotated structures with sparse rules checking.

https://lwn.net/Articles/205624/

The motivation is that it's really difficult to keep in sync all the format
strings, and although there may be ways to deal with it, I rather prefer
this other design.

On Mon, Oct 5, 2015 at 10:25 AM Javier Domingo Cansino <javierdo1 at gmail.com>
wrote:

> Hello,
>
> I have been asked for examples and use cases. Github repo has been updated.
>
> I do also have doubts on if it's worth it. If a library like this existed
> I would be definitely using it, make conversions, does take care of
> alignment, can manage unaligned data and endianness. etc.
>
> But I am not really sure if someone apart from me would find it
> interesting (long time ago I haven't seen a protocol unaligned with
> different endianess).
>
> Waiting for your feedback!
>
> /*
>  * Syntax for the function is as follows.
>  *   %[p][n][a][lb][01r]{i,y,w,d,q,s}
>  *
>  *   All the characters that don't follow this will be treated as raw chars
>  *   to be written as they are.
>  *
>  * Data type
>  *   * i - bit
>  *   * y - byte
>  *   * w - 2 byte word
>  *   * d - 4 byte word
>  *   * q - 8 byte word
>  *   * s - string without termination (use strlen()+1 in quantity to null)
>  *
>  * Data value
>  *   * 0 - fill the specified space with zeros
>  *   * 1 - fill the specified space with ones
>  *   * r - fill the specified space with random data
>  *
>  *   String data type is not valid in this case. When quantity is also
>  *   specified, use l/b to separate: %5b0 -> 5 bits of value 0
>  *
>  * Endianess. No conversion by default
>  *   * l - little endian
>  *   * b - big endian
>  *
>  * Alignment. No alignment by default
>  *   * a - align this to it's datatype
>  *         bits are aligned to byte
>  *
>  * Quantity. One by default
>  *   * n - number of same datatype (placed together)
>  *         this denotes length of string, padded with 0
>  *
>  * Pointer. Default everything is passed by value
>  *   * p - specify that passed parameter is a pointer to value(s)
>  *
>  *   Obviously, when quantity is specified, and datatype is not bits, p
>  *   is required.
>  *
>  * Some examples:
>  *   * %4lw - 4 little endian 2 byte word
>  *   * %2i  - 2 bits 'ab' from value b'000000ab'
>  *   * %2bi - 2 bits 'ab' from value b'000000ba'
>  *   * %2li - 2 bits 'ab' from value b'ab000000'
>  *   * %5y
>  *
>  * Calling functions example:
>  * int32_t dw[]=[1,2,3,4]
>  *
>  * v = writebv("%lw%2i%ay%p4d", 2047, 3, 'n', dw);
>  *
>  * in a big endian computer
>  * // *v = 0xff07c06e00000001000000020000000300000004
>  *
>  * struct my_data_t {
>  *   uint16_t a;
>  *   uint8_t b:2;
>  *   uint8_t unused1:6;
>  *   uint8_t c;
>  *   uint32_t d[4];
>  * } *my_data;
>  * char letter;
>  *
>  * // If we want to have all extracted from the blob
>  * my_data = readbv(v, "%lw%2i%ay%p4d");
>  *
>  * // If we just want to extract the char
>  * readb(v, "%0w%2l0i%ay%4l0d", &letter);
>  *
>  * // We have aligned data, but if we removed the 'a' from %ay, we
>  * wouldn't have unaligned data and this would still work.
>  *
>  */
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.infradead.org/pipermail/openwrt-devel/attachments/20151005/d7601d05/attachment.htm>
-------------- next part --------------
_______________________________________________
openwrt-devel mailing list
openwrt-devel at lists.openwrt.org
https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-devel