Changeset 1d8cdb1 in mainline for uspace/lib

Timestamp:

2008-11-18T20:28:17Z (17 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

18c485a

Parents:

26fa0f9f

Message:

Avoid unnecessary block reads in block_get().

Location:

uspace/lib/libblock

Files:

• libblock.c (modified) (2 diffs)
• libblock.h (modified) (2 diffs)

uspace/lib/libblock/libblock.c

@@ -297 +297 @@
  * @param dev_handle            Device handle of the block device.
  * @param boff                  Block offset.
+ * @param flags                 If BLOCK_FLAGS_NOREAD is specified, block_get()
+ *                              will not read the contents of the block from the
+ *                              device.
  *
  * @return                      Block structure.
  */
-block_t *block_get(dev_handle_t dev_handle, bn_t boff)
+block_t *block_get(dev_handle_t dev_handle, bn_t boff, int flags)
 {
         devcon_t *devcon;
@@ -386 +389 @@
                         abort();        /* TODO: block_write() */
                 }
-                /*
-                 * The block contains old or no data. We need to read the new
-                 * contents from the device.
-                 */
-                rc = block_read(dev_handle, &bufpos, &buflen, &pos, b->data,
-                    cache->block_size, cache->block_size);
-                assert(rc == EOK);
+                if (!(flags & BLOCK_FLAGS_NOREAD)) {
+                        /*
+                         * The block contains old or no data. We need to read
+                         * the new contents from the device.
+                         */
+                        rc = block_read(dev_handle, &bufpos, &buflen, &pos,
+                            b->data, cache->block_size, cache->block_size);
+                        assert(rc == EOK);
+                }
 
                 futex_up(&b->lock);

uspace/lib/libblock/libblock.h

@@ -45 +45 @@
 #include <libadt/list.h>
 
+/*
+ * Flags that can be used with block_get().
+ */
+
+/** 
+ * This macro is a symbolic value for situations where no special flags are
+ * needed.
+ */
+#define BLOCK_FLAGS_NONE        0
+
+/**
+ * When the client of block_get() intends to overwrite the current contents of
+ * the block, this flag is used to avoid the unnecessary read.
+ */
+#define BLOCK_FLAGS_NOREAD      1
+
 typedef unsigned bn_t;  /**< Block number type. */
 
@@ -78 +94 @@
 extern int block_cache_init(dev_handle_t, size_t, unsigned);
 
-extern block_t *block_get(dev_handle_t, bn_t);
+extern block_t *block_get(dev_handle_t, bn_t, int flags);
 extern void block_put(block_t *);