Exporting array data in sysfs

[Rolf Eike Beer <eike-kernel@sf-tec.de>]

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Hi,

I would like to put the contents of an array in sysfs files. I found no simple 
way to do this, so here are my thoughts in hope someone can hand me a light.

-simple array (array of simple type like int, char* and so on)

needs:
.name, .read, .write, .num, .writenum

When exported a directory "name" is created, containing num()+1 entries. There 
is one entry for each array entry plus the special entry "n". "cat n" gives 
you the result of num, writing to num calls writenum to change the number of 
array members. If writenum is NULL the array has fixed size.

read is read(struct whatever *, int, char *). The second argument gives the 
array number, the last one the buffer to print to (as usual). write looks 
similar, just as in existing sysfs interface (e.g. device_create_file()).

-complex array (array of struct)

This is even more tricky. You can't do this now if you don't know the number 
of entries. If you do you can create a struct device_attribute (or similar) 
for every entry and have different access functions that "know" their index. 
This is horribly inefficient and ugly.

Sort of access struct could be:

.name is fmt-string containing %i (or %lli or something like this)
.members is an array of structs looking similar to what I described above for 
the simple array. Now the index gives the index of the struct.
.num, .writenum as above

Nesting them is probably not worth it at all as it would look horrible. :)

Thoughts?

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