Add cursor to File

[vinc]

No description provided.

[vinc]

Before with a cold cache:

> time pkg i spell
Retrieving "/var/pkg/spell"
Retrieving "/lib/spell/english.dict.z"
Extracting "/lib/spell/english.dict"
Executed "pkg i spell" in 12.253962s

Before with a warm cache

> time pkg i spell
Retrieving "/var/pkg/spell"
Retrieving "/lib/spell/english.dict.z"
Extracting "/lib/spell/english.dict"
Executed "pkg i spell" in 7.564066s

After with a cold cache:

> time pkg i spell
Retrieving "/var/pkg/spell"
Retrieving "/lib/spell/english.dict.z"
Extracting "/lib/spell/english.dict"
Executed "pkg i spell" in 9.260961s

After with a warm cache:

> time pkg i spell
Retrieving "/var/pkg/spell"
Retrieving "/lib/spell/english.dict.z"
Extracting "/lib/spell/english.dict"
Executed "pkg i spell" in 7.591063s

So this optimization is useful with a cold cache but not by much.

[vinc]

I tried another optimization that didn't provide any measurable gains due to the cache:

diff --git a/src/sys/fs/file.rs b/src/sys/fs/file.rs
index 1238d4f..64d4e57 100644
--- a/src/sys/fs/file.rs
+++ b/src/sys/fs/file.rs
@@ -150,13 +150,13 @@ impl FileIO for File {
                 }
                 pos += 1;
             }
-            match block.next() {
-                Some(next_block) => {
-                    addr = next_block.addr();
-                    self.cursor_addr = addr;
+            match block.next_addr() {
+                0 => return Ok(bytes),
+                next_addr => {
+                    addr = next_addr;
+                    self.cursor_addr = next_addr;
                     self.cursor_pos = pos;
                 }
-                None => return Ok(bytes),
             }
         }
     }