Alsa-Devel Archive on lore.kernel.org
 help / color / Atom feed
* [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case
@ 2019-12-23  9:33 Takashi Sakamoto
  2019-12-23  9:42 ` Takashi Sakamoto
                   ` (2 more replies)
  0 siblings, 3 replies; 6+ messages in thread
From: Takashi Sakamoto @ 2019-12-23  9:33 UTC (permalink / raw)
  To: tiwai; +Cc: alsa-devel

A design of ALSA control core allows applications to execute three
operations for TLV feature; read, write and command. Furthermore, it
allows driver developers to process the operations by two ways; allocated
array or callback function. In the former, read operation is just allowed,
thus developers uses the latter when device driver supports variety of
models or the target model is expected to dynamically change information
stored in TLV container.

The core also allows applications to lock any element so that the other
applications can't perform write operation to the element for element
value and TLV information. When the element is locked, write and command
operation for TLV information are prohibited as well as element value.
Any read operation should be allowed in the case.

At present, when an element has callback function for TLV information,
TLV read operation returns EPERM if the element is locked. On the
other hand, the read operation is success when an element has allocated
array for TLV information. In both cases, read operation is success for
element value expectedly.

This commit fixes the bug. This change can be backported to v4.14
kernel or later.
---
 sound/core/control.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/sound/core/control.c b/sound/core/control.c
index 3fa1171dc1c2..49f3428dfacb 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -1398,8 +1398,9 @@ static int call_tlv_handler(struct snd_ctl_file *file, int op_flag,
 	if (kctl->tlv.c == NULL)
 		return -ENXIO;
 
-	/* When locked, this is unavailable. */
-	if (vd->owner != NULL && vd->owner != file)
+	// Write and command operations are not allowed for locked element.
+	if (op_flag != SNDRV_CTL_TLV_OP_READ &&
+	    vd->owner != NULL && vd->owner != file)
 		return -EPERM;
 
 	return kctl->tlv.c(kctl, op_flag, size, buf);
-- 
2.20.1

_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case
  2019-12-23  9:33 [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case Takashi Sakamoto
@ 2019-12-23  9:42 ` Takashi Sakamoto
  2019-12-23 15:03 ` Takashi Iwai
  2019-12-24 12:56 ` Jaroslav Kysela
  2 siblings, 0 replies; 6+ messages in thread
From: Takashi Sakamoto @ 2019-12-23  9:42 UTC (permalink / raw)
  To: tiwai; +Cc: alsa-devel

On Mon, Dec 23, 2019 at 06:33:47PM +0900, Takashi Sakamoto wrote:
> At present, when an element has callback function for TLV information,
> TLV read operation returns EPERM if the element is locked. On the
> other hand, the read operation is success when an element has allocated
> array for TLV information. In both cases, read operation is success for
> element value expectedly.

You can regenerate the issue by executing below Python 3 scripts:
(Installation of alsa-gobject[1], PyGObject[2] and amixer(1) in
alsa-utils is required.)

After element is locked, amixer reports EPERM for any read operation of
TLV information.

```
#########after locked#########
numid=28,iface=PCM,name='Playback Channel Map'
  ; type=INTEGER,access=r---lR--,values=6,min=0,max=36,step=0
  : values=0,0,0,0,0,0
amixer: Control hw:1 element TLV read error: Operation not permitted
```

======== 8< --------
#!/usr/bin/env python3

from sys import argv,exit
import subprocess

import gi
gi.require_version('ALSACtl', '0.0')
from gi.repository import ALSACtl

def lock_elems(card, targets, locked):
    for target in targets:
        card.lock_elem(target, locked)


def run_amixer(label, targets):
    print('{:#^30}'.format(label))
    args = ['amixer', '-c', str(card_id), 'cget', '(placeholder)']
    for target in targets:
        args[4] = "iface=PCM,name='{}'".format(target.get_name())
        subprocess.run(args)


if len(argv) < 2:
    print('One argument is required for the numerical ID of soundcard.')
    exit(1)
card_id = int(argv[1])

card = ALSACtl.Card.new()
card.open(card_id)

targets = list(filter(lambda e: e.get_name().find("Channel Map") >= 0,
                  card.get_elem_id_list()))
run_amixer('before locked', targets)

lock_elems(card, targets, True)
run_amixer('after locked', targets)

lock_elems(card, targets, False)
run_amixer('after released', targets)

# The lock is surely released automatically when control character device is
# released. Thus it's safe to terminate the above codes in its middle.
======== 8< --------

[1] https://github.com/alsa-project/alsa-gobject/
[2] https://pygobject.readthedocs.io/en/latest/
_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case
  2019-12-23  9:33 [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case Takashi Sakamoto
  2019-12-23  9:42 ` Takashi Sakamoto
@ 2019-12-23 15:03 ` Takashi Iwai
  2019-12-24 10:02   ` Takashi Sakamoto
  2019-12-24 12:56 ` Jaroslav Kysela
  2 siblings, 1 reply; 6+ messages in thread
From: Takashi Iwai @ 2019-12-23 15:03 UTC (permalink / raw)
  To: Takashi Sakamoto; +Cc: alsa-devel

On Mon, 23 Dec 2019 10:33:47 +0100,
Takashi Sakamoto wrote:
> 
> A design of ALSA control core allows applications to execute three
> operations for TLV feature; read, write and command. Furthermore, it
> allows driver developers to process the operations by two ways; allocated
> array or callback function. In the former, read operation is just allowed,
> thus developers uses the latter when device driver supports variety of
> models or the target model is expected to dynamically change information
> stored in TLV container.
> 
> The core also allows applications to lock any element so that the other
> applications can't perform write operation to the element for element
> value and TLV information. When the element is locked, write and command
> operation for TLV information are prohibited as well as element value.
> Any read operation should be allowed in the case.
> 
> At present, when an element has callback function for TLV information,
> TLV read operation returns EPERM if the element is locked. On the
> other hand, the read operation is success when an element has allocated
> array for TLV information. In both cases, read operation is success for
> element value expectedly.
> 
> This commit fixes the bug. This change can be backported to v4.14
> kernel or later.

The patch looks good but your sign-off is missing...


thanks,

Takashi
_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case
  2019-12-23 15:03 ` Takashi Iwai
@ 2019-12-24 10:02   ` Takashi Sakamoto
  2019-12-24 14:31     ` Takashi Iwai
  0 siblings, 1 reply; 6+ messages in thread
From: Takashi Sakamoto @ 2019-12-24 10:02 UTC (permalink / raw)
  To: Takashi Iwai; +Cc: alsa-devel

On Mon, Dec 23, 2019 at 04:03:53PM +0100, Takashi Iwai wrote:
> On Mon, 23 Dec 2019 10:33:47 +0100,
> Takashi Sakamoto wrote:
> > 
> > A design of ALSA control core allows applications to execute three
> > operations for TLV feature; read, write and command. Furthermore, it
> > allows driver developers to process the operations by two ways; allocated
> > array or callback function. In the former, read operation is just allowed,
> > thus developers uses the latter when device driver supports variety of
> > models or the target model is expected to dynamically change information
> > stored in TLV container.
> > 
> > The core also allows applications to lock any element so that the other
> > applications can't perform write operation to the element for element
> > value and TLV information. When the element is locked, write and command
> > operation for TLV information are prohibited as well as element value.
> > Any read operation should be allowed in the case.
> > 
> > At present, when an element has callback function for TLV information,
> > TLV read operation returns EPERM if the element is locked. On the
> > other hand, the read operation is success when an element has allocated
> > array for TLV information. In both cases, read operation is success for
> > element value expectedly.
> > 
> > This commit fixes the bug. This change can be backported to v4.14
> > kernel or later.
> 
> The patch looks good but your sign-off is missing...

Oops, I was in the festive mood...

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Besides, let us backport this patch to older kernels? As long as I
investigate, this bug exists since v2.6.19 kernel, in which TLV feature
was firstly introduced and extended[1]. When I worked for refactoring to
control core in v4,14 kernel, the bug remains kept as is[2].

It's possible to apply this patch to the longterm v4.14.160 kernel. But
when fixing this bug for the older kernels. we need to prepare an
alternative patch. In my opinion, the disadvantage of the bug is not so
critical, thus it's reasonable to abandon the older kernels.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/commit/?h=8aa9b586e4209
[2] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/commit/?h=450296f305f13


Regards

Takashi Sakamoto
_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case
  2019-12-23  9:33 [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case Takashi Sakamoto
  2019-12-23  9:42 ` Takashi Sakamoto
  2019-12-23 15:03 ` Takashi Iwai
@ 2019-12-24 12:56 ` Jaroslav Kysela
  2 siblings, 0 replies; 6+ messages in thread
From: Jaroslav Kysela @ 2019-12-24 12:56 UTC (permalink / raw)
  To: alsa-devel; +Cc: Takashi Iwai

Dne 23. 12. 19 v 10:33 Takashi Sakamoto napsal(a):
> A design of ALSA control core allows applications to execute three
> operations for TLV feature; read, write and command. Furthermore, it
> allows driver developers to process the operations by two ways; allocated
> array or callback function. In the former, read operation is just allowed,
> thus developers uses the latter when device driver supports variety of
> models or the target model is expected to dynamically change information
> stored in TLV container.
> 
> The core also allows applications to lock any element so that the other
> applications can't perform write operation to the element for element
> value and TLV information. When the element is locked, write and command
> operation for TLV information are prohibited as well as element value.
> Any read operation should be allowed in the case.
> 
> At present, when an element has callback function for TLV information,
> TLV read operation returns EPERM if the element is locked. On the
> other hand, the read operation is success when an element has allocated
> array for TLV information. In both cases, read operation is success for
> element value expectedly.
> 
> This commit fixes the bug. This change can be backported to v4.14
> kernel or later.
> ---
>   sound/core/control.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/core/control.c b/sound/core/control.c
> index 3fa1171dc1c2..49f3428dfacb 100644
> --- a/sound/core/control.c
> +++ b/sound/core/control.c
> @@ -1398,8 +1398,9 @@ static int call_tlv_handler(struct snd_ctl_file *file, int op_flag,
>   	if (kctl->tlv.c == NULL)
>   		return -ENXIO;
>   
> -	/* When locked, this is unavailable. */
> -	if (vd->owner != NULL && vd->owner != file)
> +	// Write and command operations are not allowed for locked element.
> +	if (op_flag != SNDRV_CTL_TLV_OP_READ &&
> +	    vd->owner != NULL && vd->owner != file)
>   		return -EPERM;
>   
>   	return kctl->tlv.c(kctl, op_flag, size, buf);
> 

Thanks. Good catch. I would change only the comment back to /* */ to be
consistent with the other sound/core code.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>


-- 
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case
  2019-12-24 10:02   ` Takashi Sakamoto
@ 2019-12-24 14:31     ` Takashi Iwai
  0 siblings, 0 replies; 6+ messages in thread
From: Takashi Iwai @ 2019-12-24 14:31 UTC (permalink / raw)
  To: Takashi Sakamoto; +Cc: alsa-devel

On Tue, 24 Dec 2019 11:02:10 +0100,
Takashi Sakamoto wrote:
> 
> On Mon, Dec 23, 2019 at 04:03:53PM +0100, Takashi Iwai wrote:
> > On Mon, 23 Dec 2019 10:33:47 +0100,
> > Takashi Sakamoto wrote:
> > > 
> > > A design of ALSA control core allows applications to execute three
> > > operations for TLV feature; read, write and command. Furthermore, it
> > > allows driver developers to process the operations by two ways; allocated
> > > array or callback function. In the former, read operation is just allowed,
> > > thus developers uses the latter when device driver supports variety of
> > > models or the target model is expected to dynamically change information
> > > stored in TLV container.
> > > 
> > > The core also allows applications to lock any element so that the other
> > > applications can't perform write operation to the element for element
> > > value and TLV information. When the element is locked, write and command
> > > operation for TLV information are prohibited as well as element value.
> > > Any read operation should be allowed in the case.
> > > 
> > > At present, when an element has callback function for TLV information,
> > > TLV read operation returns EPERM if the element is locked. On the
> > > other hand, the read operation is success when an element has allocated
> > > array for TLV information. In both cases, read operation is success for
> > > element value expectedly.
> > > 
> > > This commit fixes the bug. This change can be backported to v4.14
> > > kernel or later.
> > 
> > The patch looks good but your sign-off is missing...
> 
> Oops, I was in the festive mood...
> 
> Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
> 
> Besides, let us backport this patch to older kernels? As long as I
> investigate, this bug exists since v2.6.19 kernel, in which TLV feature
> was firstly introduced and extended[1]. When I worked for refactoring to
> control core in v4,14 kernel, the bug remains kept as is[2].
> 
> It's possible to apply this patch to the longterm v4.14.160 kernel. But
> when fixing this bug for the older kernels. we need to prepare an
> alternative patch. In my opinion, the disadvantage of the bug is not so
> critical, thus it's reasonable to abandon the older kernels.

I don't think we need a stable backport.  It's no regression, as you
pointed, and nothing leading to a serious problem like a crash.

So I merged now to for-next branch for 5.6 branch without
Cc-to-stable.  Also corrected the comment in C style as Jaroslav
suggested, too.


thanks,

Takashi

> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/commit/?h=8aa9b586e4209
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/commit/?h=450296f305f13
> 
> 
> Regards
> 
> Takashi Sakamoto
> 
_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, back to index

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-12-23  9:33 [alsa-devel] [PATCH] ALSA: ctl: allow TLV read operation for callback type of element in locked case Takashi Sakamoto
2019-12-23  9:42 ` Takashi Sakamoto
2019-12-23 15:03 ` Takashi Iwai
2019-12-24 10:02   ` Takashi Sakamoto
2019-12-24 14:31     ` Takashi Iwai
2019-12-24 12:56 ` Jaroslav Kysela

Alsa-Devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/alsa-devel/0 alsa-devel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 alsa-devel alsa-devel/ https://lore.kernel.org/alsa-devel \
		alsa-devel@alsa-project.org
	public-inbox-index alsa-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.alsa-project.alsa-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git