libblock: Add read-ahead task

Read-ahead requests were previously executed in the context of the
reading task.  This blocks the reading task until the complete read
with read-ahead transfer is finished.  A read-ahead task is introduced
to off-load the read-ahead transfer.  This allows the reading task to
work with the requested block more quickly.  The read-ahead is triggered
after two misses of ascending consecutive blocks or a read hit of a
block read by the most-recent read-ahead transfer.  The read-ahead
feature is configurable and can be disabled.

1 files changed, 2 insertions, 0 deletions

diff --git a/cpukit/libblock/src/diskdevs-init.c b/cpukit/libblock/src/diskdevs-init.c
index ccf954a49a..5ec96b250c 100644
--- a/cpukit/libblock/src/diskdevs-init.c
+++ b/cpukit/libblock/src/diskdevs-init.c
@@ -36,6 +36,7 @@ rtems_status_code rtems_disk_init_phys(
   dd->media_block_size = block_size;
   dd->ioctl = handler;
   dd->driver_data = driver_data;
+  dd->read_ahead.trigger = RTEMS_DISK_READ_AHEAD_NO_TRIGGER;
 
   if (block_count > 0) {
     if ((*handler)(dd, RTEMS_BLKIO_CAPABILITIES, &dd->capabilities) != 0) {
@@ -67,6 +68,7 @@ rtems_status_code rtems_disk_init_log(
   dd->media_block_size = phys_dd->media_block_size;
   dd->ioctl = phys_dd->ioctl;
   dd->driver_data = phys_dd->driver_data;
+  dd->read_ahead.trigger = RTEMS_DISK_READ_AHEAD_NO_TRIGGER;
 
   if (phys_dd->phys_dev == phys_dd) {
     rtems_blkdev_bnum phys_block_count = phys_dd->size;