Currently the ALSA proc handler allows read or write even if the proc
file were write-only or read-only.  It's mostly harmless, does thing
but allocating memory and ignores the input/output.  But it doesn't
tell user about the invalid use, and it's confusing and inconsistent
in comparison with other proc files.

This patch adds some sanity checks and let the proc handler returning
an -EIO error when the invalid read/write is performed.

Cc: <stable@vger.kernel.org> # v4.2+
Signed-off-by: Takashi Iwai <tiwai@suse.de>

The ALSA proc handler allows currently the write in the unlimited size
until kmalloc() fails.  But basically the write is supposed to be only
for small inputs, mostly for one line inputs, and we don't have to
handle too large sizes at all.  Since the kmalloc error results in the
kernel warning, it's better to limit the size beforehand.

This patch adds the limit of 16kB, which must be large enough for the
currently existing code.

Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Takashi Iwai <tiwai@suse.de>

It's no longer a part of API but merely a local function.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

Just a minor refactoring, no functional changes.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

The commit [c560a6797e3b: ALSA: core: Remove child proc file elements
recursively] converted snd_card_proc_new() with the normal
snd_info_*() call and removed snd_device chain for such info
entries. However, it misses one point: the creation of the proc entry
was managed by snd_device chain in the former code, and now it's also
gone, which results in no proc files creation at all.  Mea culpa.

This patch makes snd_info_card_register() creating the all pending
child proc entries in a shot.  Also, since snd_card_register() might
be called multiple times, this function is also changed to be callable
multiple times.

Along with the changes above, now the linked list of snd_info_entry is
added at creation time instead of snd_info_register() for keeping eyes
of pending info entries.

Fixes: c560a6797e3b ('ALSA: core: Remove child proc file elements recursively')
Reported-by: "Lu, Han" <han.lu@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

snd_info_free_entry() releases the all children nodes as well, but due
to the wrong timing of releasing the link, the children nodes may be
disconnected but left unreleased.  This patch fixes it by moving the
link free at the right position.  Also it eases list_for_each_entry()
without _safe option in snd_info_disconnect() because it no longer
frees the children nodes there.

Fixes: c560a6797e3b ('ALSA: core: Remove child proc file elements recursively')
Signed-off-by: Takashi Iwai <tiwai@suse.de>

A few minor cleanups:
- Move the call of snd_info_minor_register() into snd_info_init() so
  that we can call all proc-related stuff in a shot
- Add missing __init prefix to snd_info_minor_register()
- Return an error properly from snd_oss_info_register()
- Drop snd_info_minor_unregister() that is superfluous now

Acked-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Minor cleanups of Makefile to build some codes conditionally so that
a few ifdefs can be reduced.

Acked-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

So far we've ignored the errors at creating proc files in many places.
But they should be rather treated seriously.

Also, by assuring the error handling, we can get rid of superfluous
snd_info_free_entry() calls as they will be removed by the parent in
the caller side.

This patch fixes the missing error checks and reduces the superfluous
free calls.

Acked-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Since each proc entry is freed automatically by the parent, we don't
have to take care of its life cycle any longer.  This allows us to
reduce a few more lines of codes.

Acked-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>