[PATCH libxkbcommon] keymap: add xkb_keymap_new_from_memory()

[Ran Benita]

On Mon, Mar 11, 2013 at 12:53:39PM +0100, David Herrmann wrote:
> The current API doesn't allow the caller to create keymaps from mmap()'ed
> files. The problem is, xkb_keymap_new_from_string() requires a terminating
> 0 byte. However, there is no way to guarantee that when using mmap() so a
> user currently has to copy the whole file just to get the terminating zero
> byte (assuming they cannot use xkb_keymap_new_from_file()).
> 
> This adds a new entry xkb_keymap_new_from_memory() which takes a memory
> location and the size in bytes.
> 
> Internally, we depend on yy_scan_{string,byte}() helpers. According to
> flex documentation these already copy the input string because they are
> wrappers around yy_scan_buffer().
> yy_scan_buffer() on the other hand has some insane requirements. The
> buffer must be writeable and the last two bytes must be ASCII-NUL. But the
> buffer may contain other 0 bytes just fine.
> 
> Because we don't want these constraints in our public API,
> xkb_keymap_new_from_memory() needs to create a copy of the input memory.
> But it then calls yy_scan_buffer() directly. Hence, we have the same
> number of buffer-copies as with *_from_string() but without the
> terminating 0 requirement.
> 
> Maybe some day we no longer depend on flex and can have a zero-copy API. A
> user could mmap() a file and it would get parsed right from this buffer.
> But until then, we shouldn't expose this limitation in the API but instead
> provide an API that some day can work with zero-copy.
> 
> Signed-off-by: David Herrmann <dh.herrmann at gmail.com>

Patch looks good to me. Too bad we need the extra entry point.

As a side note to your last point: replacing flex is pretty easy, in
fact I've done it some months ago. I decided against it though because
flex files are nice and declarative and there wasn't a good reason to
replace it. But I've done a quick rebase now on top of my working branch
and your patch:
https://github.com/bluetech/libxkbcommon/commits/scanner-wip
Maybe it's worth it now.

Thanks,
Ran