[libdvdcss-devel] [PATCH] Read 50 sectors in advance during CSS key computation

[Diego Biurrun]

From: David Dielsky <david122192 at gmail.com>

This reduces the number of read accesses.

Signed-off-by: Diego Biurrun <diego at biurrun.de>
---

This is still a horrible hack.  I fail to see the purpose of reading
data from the DVD into a dummy buffer, only to then reset the offset
pointer and read the data that actually gets processed from the DVD
again ...

 src/css.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/src/css.c b/src/css.c
index b70759a..ee94548 100644
--- a/src/css.c
+++ b/src/css.c
@@ -1493,6 +1493,15 @@ static int CrackTitleKey( dvdcss_t dvdcss, int i_pos, int i_len,
     int b_read_error = 0;
     int i_ret;
 
+    /* Read 50 sectors in advance into a dummy buffer, in order to keep the
+     * data in the OS buffers and reduce the number of read accesses. */
+    const int nb_sectors = 50;
+    void *null_buffer = malloc( nb_sectors * DVDCSS_BLOCK_SIZE );
+    if( !null_buffer )
+    {
+        return -1;
+    }
+
     print_debug( dvdcss, "cracking title key at block %i", i_pos );
 
     i_tries = 0;
@@ -1507,6 +1516,13 @@ static int CrackTitleKey( dvdcss_t dvdcss, int i_pos, int i_len,
             print_error( dvdcss, "seek failed" );
         }
 
+        // every 50 sectors, read 50 sectors
+        if ( i_reads % nb_sectors == 0 )
+        {
+            dvdcss_read(dvdcss, null_buffer, nb_sectors, DVDCSS_NOFLAGS);
+            dvdcss->pf_seek( dvdcss, i_pos );
+        }
+
         i_ret = dvdcss_read( dvdcss, p_buf, 1, DVDCSS_NOFLAGS );
 
         /* Either we are at the end of the physical device or the auth
@@ -1585,6 +1601,8 @@ static int CrackTitleKey( dvdcss_t dvdcss, int i_pos, int i_len,
         print_debug( dvdcss, "end of title reached" );
     }
 
+    free( null_buffer );
+
     /* Print some statistics. */
     print_debug( dvdcss, "successful attempts %d/%d, scrambled blocks %d/%d",
                          i_success, i_tries, i_encrypted, i_reads );
-- 
1.9.1