libfile: Change write_full to be have const buf ...

write() uses a const pointer so write_full should do the same.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

move unlink_recursive declaration to libfile.h ...

unlink_recursive is a file utility function, so move the prototype to
libfile.h

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

move make_directory declaration to libfile.h ...

As a utility function for file handling make_directory() is well
suited for libfile. Move it there.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

libfile: move open_and_lseek() to libfile ...

libfile is a collection of helpers for handling files. open_and_lseek()
is a perfect match for this, so move it there.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

libfile: Add copy_recursive ...

To recursively copy a directory tree.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

libfile: add compare_file function ...

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

read_file: introduce read_file_2 ...

read_file has some limitations:

- It is not possible to check the error code since read_file returns
  NULL for failure
- It is not possible to limit the buffer size to sensible limits.

This patch introduces read_file_2 which doesn't have these limitations.
read_file becomes a wrapper around read_file_2.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

move file helper functions to separate file ...

We have our file helper functions in several places. Move them
all to lib/libfile.c.
With this we no longer have file helpers in fs/fs.c which contains
the core fs functions and no functions in lib/libbb.c which are
not from busybox.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>