Re: [alsa-devel] [PATCH] Emit an error message when dlopen fails.

22 Nov 2017

Hi,
On Nov 22 2017 07:12, Cedric Roux wrote:
...
Signed-off-by: Cedric Roux sed@free.fr
src/dlmisc.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git src/dlmisc.c src/dlmisc.c
index f154ebd0..9e8e401e 100644
--- src/dlmisc.c
+++ src/dlmisc.c
@@ -81,10 +81,14 @@ void *snd_dlopen(const char *name, int mode)
   	strcat(filename, "/");
   	strcat(filename, name);
   	handle = dlopen(filename, mode);

if (!handle)


	SNDERR("snd_dlopen: %s: %s", filename, dlerror());

free(filename);
}
if (!handle)
handle = dlopen(name, mode);
if (!handle)
SNDERR("snd_dlopen: %s: %s", name, dlerror());

return handle;
#else
return NULL;

In my opinion, this patch is preferable, however it can always generate 
superfluous error messages when handling hook configuration on 
'alsa.conf'. For example:
$ LD_PRELOAD=./src/.libs/libasound.so.2.0.0 amixer
ALSA lib dlmisc.c:85:(snd_dlopen) snd_dlopen: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
cannot open shared object file: No such file or directory
ALSA lib dlmisc.c:85:(snd_dlopen) snd_dlopen: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
cannot open shared object file: No such file or directory
ALSA lib dlmisc.c:85:(snd_dlopen) snd_dlopen: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
cannot open shared object file: No such file or directory
ALSA lib dlmisc.c:85:(snd_dlopen) snd_dlopen: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
cannot open shared object file: No such file or directory
ALSA lib dlmisc.c:85:(snd_dlopen) snd_dlopen: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
cannot open shared object file: No such file or directory
ALSA lib dlmisc.c:85:(snd_dlopen) snd_dlopen: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
/usr/lib/x86_64-linux-gnu/alsa-lib//./src/.libs/libasound.so.2.0.0: 
cannot open shared object file: No such file or directory
Simple mixer control 'IEC958',0
   Capabilities: pswitch pswitch-joined
   Playback channels: Mono
   Mono: Playback [on]
...
When any hook configuration includes no lines with 'lib', 'snd_dlopen()' 
gets NULL as its first argument, then 'dlopen()' gets an inexistent path 
as its first argument, like:
(parsing alsa.conf)
snd_config_hooks_call()
   ->snd_dlopen(name = NULL)
     if (name == NULL)
       name = self
     filename = ALSA_PLUGIN_DIR + '/' + name
     dlopen(filename)
     (generate the error messages)
I don't know why alsa-lib is programmed as what it is, so have no idea 
to suggest better solution...
Additionally, your patch includes some issues of patch format:
* Not only your signature but also patch comment is required. The first
   line is interpreted as patch title, and the rest is as comment.
* Patches should be compliant to git-patch format. I encountered failure
   of 'git am' for this patch. Please use 'git format-patch' command to
   generate patches for posting.
When posting patches, please take care of the above.
Regards
Takashi Sakamoto

    