Add facilities to report and enrich error messages.

The idea is that a given error should be reported only once to the user.
At the moment, for example, we can get:
- "no suitable access module" (printed by module_Need)
 - "unable to create access" (printed by input/access)
 - "unable to open stream" (printed by input/input)
 - ...

The facilities provided here are:
* msg_StackSet( code, message ) : "throw" a new error
* msg_StackAdd( message ) : Append a message allowing to trace the message
* msg_StackMsg() : Retrieve the message

So, in the previous example, module_Need would msg_StackSet( code, "no
suitable access module"), then input/input would add "unable to create
access" and finally, input/input can print the "unable to open stream:
unable to create access: no suitable module" message.

The three functions are context-free, you don't need a vlc_object, so
that we can add verbose error reporting everywhere.

include/vlc_common.h

@@ -1177,6 +1177,14 @@ VLC_EXPORT( const char *, VLC_Changeset, ( void ) );
 #include "main.h"
 #include "vlc_configuration.h"
 
+/** The global thread var for msg stack context
+ *  We store this as a static global variable so we don't need a vlc_object_t
+ *  everywhere.
+ *  This key is created in vlc_threads_init and is therefore ready to use at
+ *  the very beginning of the universe */
+extern vlc_threadvar_t msg_context_global_key;
+
+
 #if defined( __BORLANDC__ )
 #   undef PACKAGE
 #   define PACKAGE

include/vlc_messages.h

@@ -44,9 +44,19 @@ int vlc_mutex_unlock(  vlc_mutex_t * ) ;
  * @{
  */
 
+/** Internal message stack context */
+typedef struct
+{
+    int i_code;
+    char * psz_message;
+} msg_context_t;
+
+VLC_EXPORT( void,  msg_StackSet, ( int, const char*, ... ) );
+VLC_EXPORT( void,  msg_StackAdd, ( const char*, ... ) );
+VLC_EXPORT( const char*, msg_StackMsg, ( void ) );
 
 /**
- * Store a single message.
+ * Store a single message sent to user.
  */
 typedef struct
 {

include/vlc_threads.h

@@ -29,6 +29,9 @@
   #error You are not libvlc or one of its plugins. You cannot include this file
 #endif
 
+#ifndef _VLC_THREADS_H_
+#define _VLC_THREADS_H_
+
 #include <stdio.h>
 
 #if defined(DEBUG) && defined(HAVE_SYS_TIME_H)
@@ -274,3 +277,4 @@ typedef struct
 
 #endif
 
+#endif

include/vlc_threads_funcs.h

@@ -29,6 +29,9 @@
   #error You are not libvlc or one of its plugins. You cannot include this file
 #endif
 
+#ifndef _VLC_THREADFUNCS_H_
+#define _VLC_THREADFUNCS_H_
+
 /*****************************************************************************
  * Function definitions
  *****************************************************************************/
@@ -557,11 +560,7 @@ static inline int __vlc_cond_wait( const char * psz_file, int i_line,
 /*****************************************************************************
  * vlc_threadvar_set: create: set the value of a thread-local variable
  *****************************************************************************/
-#define vlc_threadvar_set( P_TLS , P_VAL )                                   \
-   __vlc_threadvar_set( __FILE__, __LINE__, P_TLS, P_VAL )
-
-static inline int __vlc_threadvar_set( char* psz_file, int line,
-                                        vlc_threadvar_t * p_tls, void *p_value )
+static inline int vlc_threadvar_set( vlc_threadvar_t * p_tls, void *p_value )
 {
     int i_ret;
 
@@ -588,11 +587,7 @@ static inline int __vlc_threadvar_set( char* psz_file, int line,
 /*****************************************************************************
  * vlc_threadvar_get: create: get the value of a thread-local variable
  *****************************************************************************/
-#define vlc_threadvar_get( P_TLS )                                         \
-   __vlc_threadvar_get( __FILE__, __LINE__, P_TLS )
-
-static inline void* __vlc_threadvar_get( char* psz_file, int line,
-                                         vlc_threadvar_t * p_tls )
+static inline void* vlc_threadvar_get( vlc_threadvar_t * p_tls )
 {
     void* p_ret;
 
@@ -641,3 +636,5 @@ static inline void* __vlc_threadvar_get( char* psz_file, int line,
  *****************************************************************************/
 #define vlc_thread_join( P_THIS )                                           \
     __vlc_thread_join( VLC_OBJECT(P_THIS), __FILE__, __LINE__ )
+
+#endif

src/input/access.c

@@ -101,6 +101,7 @@ static access_t *access2_InternalNew( vlc_object_t *p_obj, const char *psz_acces
 
     if( p_access->p_module == NULL )
     {
+        msg_StackAdd( "could not create access" );
         vlc_object_detach( p_access );
         free( p_access->psz_access );
         free( p_access->psz_path );

src/input/input.c

@@ -2073,7 +2073,8 @@ static int InputSourceInit( input_thread_t *p_input,
 
         if( in->p_access == NULL )
         {
-            msg_Err( p_input, "no suitable access module for `%s'", psz_mrl );
+            msg_Err( p_input, "open of `%s' failed: %s", psz_mrl,
+                                                         msg_StackMsg() );
             intf_UserFatal( VLC_OBJECT( p_input), VLC_FALSE,
                             _("Your input can't be opened"),
                             _("VLC is unable to open the MRL '%s'."

src/misc/messages.c

@@ -583,3 +583,64 @@ static void PrintMsg ( vlc_object_t * p_this, msg_item_t * p_item )
 #   endif
 #endif
 }
+
+static msg_context_t* GetContext(void)
+{
+    msg_context_t *p_ctx = vlc_threadvar_get( &msg_context_global_key );
+    if( p_ctx == NULL )
+    {
+        MALLOC_NULL( p_ctx, msg_context_t );
+        p_ctx->psz_message = NULL;
+        vlc_threadvar_set( &msg_context_global_key, p_ctx );
+    }
+    return p_ctx;
+}
+
+void msg_StackSet( int i_code, const char *psz_message, ... )
+{
+    va_list ap;
+    msg_context_t *p_ctx = GetContext();
+    assert( p_ctx );
+    va_start( ap, psz_message );
+    if( p_ctx->psz_message != NULL )
+    {
+        free( p_ctx->psz_message );
+    }
+
+    vasprintf( &p_ctx->psz_message, psz_message, ap );
+    va_end( ap );
+    p_ctx->i_code = i_code;
+}
+
+void msg_StackAdd( const char *psz_message, ... )
+{
+    char *psz_tmp;
+    va_list ap;
+    msg_context_t *p_ctx = GetContext();
+    assert( p_ctx );
+
+    va_start( ap, psz_message );
+    vasprintf( &psz_tmp, psz_message, ap );
+    va_end( ap );
+
+    if( !p_ctx->psz_message )
+        p_ctx->psz_message = psz_tmp;
+    else
+    {
+        char *psz_old = malloc( strlen( p_ctx->psz_message ) + 1 );
+        memcpy( psz_old, p_ctx->psz_message, strlen( p_ctx->psz_message ) + 1 );
+        p_ctx->psz_message = realloc( p_ctx->psz_message,
+                                      strlen( p_ctx->psz_message ) +
+                                      /* ':', ' ', '0' */
+                                      strlen( psz_tmp ) + 3 );
+        sprintf( p_ctx->psz_message, "%s: %s", psz_tmp, psz_old );
+        free( psz_tmp ); free( psz_old );
+    }
+}
+
+const char* msg_StackMsg( void )
+{
+    msg_context_t *p_ctx = GetContext();
+    assert( p_ctx );
+    return p_ctx->psz_message;
+}

src/misc/modules.c

@@ -699,6 +699,9 @@ module_t * __module_Need( vlc_object_t *p_this, const char *psz_capability,
         {
             msg_Err( p_this, "no %s module matched \"%s\"",
                  psz_capability, (psz_name && *psz_name) ? psz_name : "any" );
+
+            msg_StackSet( VLC_EGENERIC, "no %s module matched \"%s\"",
+                 psz_capability, (psz_name && *psz_name) ? psz_name : "any" );
         }
     }
     else if( psz_name != NULL && *psz_name )
@@ -706,6 +709,8 @@ module_t * __module_Need( vlc_object_t *p_this, const char *psz_capability,
         msg_Warn( p_this, "no %s module matching \"%s\" could be loaded",
                   psz_capability, (psz_name && *psz_name) ? psz_name : "any" );
     }
+    else
+        msg_StackSet( VLC_EGENERIC, "no suitable %s module", psz_capability );
 
     if( psz_shortcuts )
     {

src/misc/threads.c

@@ -49,6 +49,8 @@ static vlc_object_t *p_root;
 #elif defined( HAVE_CTHREADS_H )
 #endif
 
+vlc_threadvar_t msg_context_global_key;
+
 /*****************************************************************************
  * vlc_threads_init: initialize threads system
  *****************************************************************************
@@ -130,6 +132,8 @@ int __vlc_threads_init( vlc_object_t *p_this )
             i_initializations++;
             i_status = VLC_THREADS_READY;
         }
+
+        vlc_threadvar_create( p_root, &msg_context_global_key );
     }
     else
     {
@@ -505,30 +509,25 @@ int __vlc_cond_destroy( const char * psz_file, int i_line, vlc_cond_t *p_condvar
  *****************************************************************************/
 int __vlc_threadvar_create( vlc_object_t *p_this, vlc_threadvar_t *p_tls )
 {
+    int i_ret;
 #if defined( PTH_INIT_IN_PTH_H )
-    return pth_key_create( &p_tls->handle, NULL );
+    i_ret = pth_key_create( &p_tls->handle, NULL );
 #elif defined( HAVE_KERNEL_SCHEDULER_H )
     msg_Err( p_this, "TLS not implemented" );
-    return VLC_EGENERIC;
+    i_ret VLC_EGENERIC;
 #elif defined( ST_INIT_IN_ST_H )
-    return st_key_create( &p_tls->handle, NULL );
+    i_ret = st_key_create( &p_tls->handle, NULL );
 #elif defined( UNDER_CE ) || defined( WIN32 )
 #elif defined( WIN32 )
     p_tls->handle = TlsAlloc();
-    if( p_tls->handle == 0xFFFFFFFF )
-    {
-        return VLC_EGENERIC;
-    }
-
-    msg_Err( p_this, "TLS not implemented" );
-    return VLC_EGENERIC;
+    i_ret = !( p_tls->handle == 0xFFFFFFFF );
 
 #elif defined( PTHREAD_COND_T_IN_PTHREAD_H )
-    return pthread_key_create( &p_tls->handle, NULL );
-
+    i_ret =  pthread_key_create( &p_tls->handle, NULL );
 #elif defined( HAVE_CTHREADS_H )
-    return cthread_keycreate( &p_tls-handle );
+    i_ret = cthread_keycreate( &p_tls-handle );
 #endif
+    return i_ret;
 }
 
 /*****************************************************************************