Add the get_sd_card_usage function to the Storage struct

This patch adds support for the NK_get_SD_usage_data function.  It
returns a range of the SD card that has not been accessed during this
power cycle.

1 files changed, 41 insertions, 1 deletions

diff --git a/src/device/storage.rs b/src/device/storage.rs
index 08ec4e9..a2c598b 100644
--- a/src/device/storage.rs
+++ b/src/device/storage.rs
@@ -1,7 +1,8 @@
-// Copyright (C) 2019-2019 Robin Krahl <robin.krahl@ireas.org>
+// Copyright (C) 2019-2020 Robin Krahl <robin.krahl@ireas.org>
 // SPDX-License-Identifier: MIT
 
 use std::fmt;
+use std::ops;
 
 use nitrokey_sys;
 
@@ -635,6 +636,45 @@ impl<'a> Storage<'a> {
         })
     }
 
+    /// Returns a range of the SD card that has not been used to during this power cycle.
+    ///
+    /// The Nitrokey Storage tracks read and write access to the SD card during a power cycle.
+    /// This method returns a range of the SD card that has not been accessed during this power
+    /// cycle.  The range is relative to the total size of the SD card, so both values are less
+    /// than or equal to 100.  This can be used as a guideline when creating a hidden volume.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// let mut manager = nitrokey::take()?;
+    /// let storage = manager.connect_storage()?;
+    /// let usage = storage.get_sd_card_usage()?;
+    /// println!("SD card usage: {}..{}", usage.start, usage.end);
+    /// # Ok::<(), nitrokey::Error>(())
+    /// ```
+    pub fn get_sd_card_usage(&self) -> Result<ops::Range<u8>, Error> {
+        let mut usage_data = nitrokey_sys::NK_SD_usage_data {
+            write_level_min: 0,
+            write_level_max: 0,
+        };
+        let result = unsafe { nitrokey_sys::NK_get_SD_usage_data(&mut usage_data) };
+        match get_command_result(result) {
+            Ok(_) => {
+                if usage_data.write_level_min > usage_data.write_level_max
+                    || usage_data.write_level_max > 100
+                {
+                    Err(Error::UnexpectedError)
+                } else {
+                    Ok(ops::Range {
+                        start: usage_data.write_level_min,
+                        end: usage_data.write_level_max,
+                    })
+                }
+            }
+            Err(err) => Err(err),
+        }
+    }
+
     /// Blinks the red and green LED alternatively and infinitely until the device is reconnected.
     pub fn wink(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_wink() })