[vlc-devel] [PATCH v3 14/14] record: avoid pointless file creation for probing

[Lyndon Brown]

From: Lyndon Brown <jnqnfe at gmail.com>
Date: Wed, 14 Oct 2020 02:51:14 +0100
Subject: record: avoid pointless file creation for probing

when probing muxers we don't really need the temporary file to exist in the
filesystem, we can use vlc_memfd() and pass along the file descriptor for
duplication in the file access module.

OutputNew() takes a new 'fd' param, and when probing we use that to pass
in the FD returned by vlc_memfd(), with a NULL for the path. Otherwise we
provide a path and -1 for 'fd'. If 'fd' is -1 it uses 'file' as the access
module and the specified path. If 'fd' is not -1, it uses the FD converted
to a string as the path and 'fd' as the access module. (same module,
different shortcut, which just triggers FD mode via the different access
name).

diff --git a/modules/stream_out/record.c b/modules/stream_out/record.c
index 53cc812069..6c8a758ea5 100644
--- a/modules/stream_out/record.c
+++ b/modules/stream_out/record.c
@@ -314,31 +314,45 @@ static const muxer_properties_t p_muxers[] = {
 };
 #undef M
 
-static int OutputNew( sout_stream_t *p_stream,
-                      const char *psz_muxer, const char *psz_prefix, const char *psz_extension  )
+static int OutputNew( sout_stream_t *p_stream, const char *psz_muxer, int fd,
+                      const char *psz_prefix, const char *psz_extension  )
 {
     sout_stream_sys_t *p_sys = p_stream->p_sys;
     char *psz_file = NULL, *psz_tmp = NULL;
     char *psz_output = NULL;
+    const char *access = NULL;
     int i_count;
 
-    if( asprintf( &psz_tmp, "%s%s%s",
-                  psz_prefix, psz_extension ? "." : "", psz_extension ? psz_extension : "" ) < 0 )
+    if (fd != -1)
     {
-        goto error;
+        access = "fd";
+        if( asprintf(&psz_file, "%d", fd) < 0 )
+        {
+            goto error;
+        }
     }
-
-    psz_file = config_StringEscape( psz_tmp );
-    if( !psz_file )
+    else
     {
+        access = "file";
+
+        if( asprintf( &psz_tmp, "%s%s%s",
+                      psz_prefix, psz_extension ? "." : "", psz_extension ? psz_extension : "" ) < 0 )
+        {
+            goto error;
+        }
+
+        psz_file = config_StringEscape( psz_tmp );
+        if( !psz_file )
+        {
+            free( psz_tmp );
+            goto error;
+        }
         free( psz_tmp );
-        goto error;
     }
-    free( psz_tmp );
 
     if( asprintf( &psz_output,
-                  "std{access=file{no-append,no-format,no-overwrite},"
-                  "mux=%s,dst='%s'}", psz_muxer, psz_file ) < 0 )
+                  "std{access=%s{no-append,no-format,no-overwrite},"
+                  "mux=%s,dst='%s'}", access, psz_muxer, psz_file ) < 0 )
     {
         psz_output = NULL;
         goto error;
@@ -464,10 +478,9 @@ static void OutputStart( sout_stream_t *p_stream )
         msg_Warn( p_stream, "failed to find an adequate muxer, probing muxers" );
         for( unsigned i = 0; i < sizeof(ppsz_muxers) / sizeof(*ppsz_muxers); i++ )
         {
-            char *psz_file;
             int i_es;
 
-            int fd = vlc_MakeTmpFile(&psz_file, PACKAGE_NAME"-rec.");
+            int fd = vlc_memfd();
             if( fd == -1 )
             {
                 msg_Warn( p_stream, "failed to create temporary file" );
@@ -475,15 +488,11 @@ static void OutputStart( sout_stream_t *p_stream )
             }
 
             msg_Dbg( p_stream, "probing muxer %s", ppsz_muxers[i][0] );
-            i_es = OutputNew( p_stream, ppsz_muxers[i][0], psz_file, NULL );
+            i_es = OutputNew( p_stream, ppsz_muxers[i][0], fd, NULL, NULL );
+            vlc_close( fd );
 
             if( i_es < 0 )
-            {
-                vlc_unlink( psz_file );
-                free( psz_file );
-                vlc_close( fd );
                 continue;
-            }
 
             /* */
             for( int j = 0; j < p_sys->i_id; j++ )
@@ -506,9 +515,6 @@ static void OutputStart( sout_stream_t *p_stream )
                 if( i_best_es >= p_sys->i_id )
                     break;
             }
-            vlc_unlink( psz_file );
-            free( psz_file );
-            vlc_close( fd );
         }
 
         /* */
@@ -519,7 +525,7 @@ static void OutputStart( sout_stream_t *p_stream )
     }
 
     /* Create the output */
-    if( OutputNew( p_stream, psz_muxer, p_sys->psz_prefix, psz_extension ) < 0 )
+    if( OutputNew( p_stream, psz_muxer, -1, p_sys->psz_prefix, psz_extension ) < 0 )
     {
         msg_Err( p_stream, "failed to open output");
         return;