Changeset 746f623 in mainline for uspace/srv/fs/fat/fat_fat.c

Timestamp:

2010-07-25T22:00:10Z (14 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

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

Children:

ed6cf34b

Parents:

377cce8

Message:

Turn fat_block_get() into a real function and make it aware of the cached last
cluster number in fat_node_t. This reduces the running time of mkfile —size 5m
by ~58% under Qemu.

File:

• uspace/srv/fs/fat/fat_fat.c (modified) (1 diff)

uspace/srv/fs/fat/fat_fat.c

@@ -119 +119 @@
 
         return EOK;
+}
+
+/** Read block from file located on a FAT file system.
+ *
+ * @param block         Pointer to a block pointer for storing result.
+ * @param bs            Buffer holding the boot sector of the file system.
+ * @param nodep         FAT node.
+ * @param bn            Block number.
+ * @param flags         Flags passed to libblock.
+ *
+ * @return              EOK on success or a negative error code.
+ */
+int
+fat_block_get(block_t **block, struct fat_bs *bs, fat_node_t *nodep,
+    aoff64_t bn, int flags)
+{
+        if (!nodep->size)
+                return ELIMIT;
+
+        if (((((nodep->size - 1) / bs->bps) / bs->spc) == bn / bs->spc) &&
+            (nodep->lastc_cached_valid) && (nodep->firstc != FAT_CLST_ROOT)) {
+                /*
+                 * This is a request to read a block within the last cluster
+                 * when fortunately we have the last cluster number cached.
+                 */
+                fat_cluster_t lastc = nodep->lastc_cached_value;
+                unsigned bps;
+                unsigned rscnt;         /* block address of the first FAT */
+                unsigned rde;
+                unsigned rds;           /* root directory size */
+                unsigned sf;
+                unsigned ssa;           /* size of the system area */
+
+                bps = uint16_t_le2host(bs->bps);
+                rscnt = uint16_t_le2host(bs->rscnt);
+                rde = uint16_t_le2host(bs->root_ent_max);
+                sf = uint16_t_le2host(bs->sec_per_fat);
+
+                rds = (sizeof(fat_dentry_t) * rde) / bps;
+                rds += ((sizeof(fat_dentry_t) * rde) % bps != 0);
+                ssa = rscnt + bs->fatcnt * sf + rds;
+        
+                return block_get(block, nodep->idx->dev_handle,
+                    ssa + (lastc - FAT_CLST_FIRST) * bs->spc + bn % bs->spc,
+                    flags);
+        } else {
+                return _fat_block_get(block, bs, nodep->idx->dev_handle,
+                    nodep->firstc, bn, flags);
+        }
 }