From: Kars Mulder > Sent: 02 July 2020 22:48 > > On Thursday, July 02, 2020 09:55 CEST, David Laight wrote: > > Hmm... sscanf() is also horrid. > > Surprisingly difficult to use correctly. > > > > It is usually best to use strchr() (and maybe str[c]scn()) > > to parse strings. > > For numbers use whatever the kernels current 'favourite' implementation > > of strtoul() is called. > > I thought that using sscanf would clean up the code a bit compared to > several haphazard calls, but I can see your point about sscanf being > difficult to use correctly. > > The kernel functions kstrtou16 seem to expect a null-terminated string > as argument. Since there are no null-bytes after the numbers we want to > parse, it becomes necessary to copy at least part of the strings to a > buffer.
There ought to be one that returns a pointer to the first character that isn't converted - but I'm no expert on the full range of these functions. > If we're copying strings to buffers anyway, I think the simplest > solution would be to just kstrdup the entire parameter and not touch > the rest of the string parsing code. This has the disadvantage of > having an extra memory allocation to keep track of. > > Since the parameter is currently restricted to 128 characters at > most, it may alternatively be possible to copy the parameter to > a 128-byte buffer on the stack. This has the advantage of having > to keep track of one less memory allocation, but the disadvantage > of using 128 bytes more stack space; I'm not sure whether that's > acceptable. The problem with strdup() is you get the extra (unlikely) failure path. 128 bytes of stack won't be a problem if the function is (essentially) a leaf. Deep stack use is actually likely to be in the bowels of printf()) inside an obscure error path. Many years ago (about 1984) I parsed the object code of a program to find the deepest stack use (no recursion and no function pointers) so we could set the stack sizes correctly - there wasn't enough memory to do it properly! David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)