From 429864a69f7fe1c9cc61e7859673dd6949fbc130 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rafa=C5=82=20Harabie=C5=84?= <rafalh1992@o2.pl>
Date: Wed, 9 May 2018 15:34:41 +0200
Subject: [PATCH] Clarify that seeked filesystem is not handled by library

---
 src/fs.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/fs.rs b/src/fs.rs
index e0a965d..cac93c7 100644
--- a/src/fs.rs
+++ b/src/fs.rs
@@ -224,9 +224,16 @@ pub struct FileSystem<'a> {
 impl <'a> FileSystem<'a> {
     /// Creates new filesystem object instance.
     ///
+    /// Supplied disk parameter cannot be seeked. If there is a need to read a fragment of disk image (e.g. partition)
+    /// library user should provide a custom implementation of ReadWriteSeek trait.
+    ///
     /// Note: creating multiple filesystem objects with one underlying device/disk image can
     /// cause filesystem corruption.
     pub fn new<T: ReadWriteSeek>(disk: &'a mut T, options: FsOptions) -> io::Result<FileSystem<'a>> {
+        // Make sure given image is not seeked
+        debug_assert!(disk.seek(SeekFrom::Current(0))? == 0);
+
+        // Read boot sector
         let bpb = {
             let boot = BootRecord::deserialize(disk)?;
             if boot.boot_sig != [0x55, 0xAA] {