Manage the possibility of incomplete data read

When trying to read a StaticHeader it may be that the buffer doesn't
get filled with data from the file or device being read.

Signed-off-by: mulhern <[email protected]>

src/engine/strat_engine/metadata.rs

@@ -199,24 +199,22 @@ impl StaticHeader {
     fn setup<F>(f: &mut F) -> EngineResult<Option<StaticHeader>>
         where F: Read + Seek
     {
-        let (buf, _) = try!(StaticHeader::read_into_buf(f));
-        StaticHeader::setup_from_buf(&buf)
+        let (buf, bytes) = try!(StaticHeader::read_into_buf(f));
+        StaticHeader::setup_from_buf(&buf, bytes)
     }
 
     /// Try to find a valid StaticHeader in a buffer.
     /// If there is an error in reading the first, try the next. If there is
     /// no error in reading the first, assume it is correct, i.e., do not
     /// verify that it matches the next.
     /// Return None if the static header's magic number is wrong.
-    fn setup_from_buf(buf: &[u8; _BDA_STATIC_HDR_SIZE]) -> EngineResult<Option<StaticHeader>> {
-        let sigblock_spots = [&buf[SIGBLOCK_REGION_ONE.0..SIGBLOCK_REGION_ONE.1],
-                              &buf[SIGBLOCK_REGION_TWO.0..SIGBLOCK_REGION_TWO.1]];
-
+    fn setup_from_buf(buf: &[u8; _BDA_STATIC_HDR_SIZE],
+                      bytes: usize)
+                      -> EngineResult<Option<StaticHeader>> {
         // TODO: repair static header if one incorrect?
-        for buf in &sigblock_spots {
-            match StaticHeader::sigblock_from_buf(buf, buf.len()) {
-                Ok(val) => return Ok(val),
-                _ => continue,
+        for &(start, end) in &[SIGBLOCK_REGION_ONE, SIGBLOCK_REGION_TWO] {
+            if let Ok(val) = StaticHeader::sigblock_from_buf(&buf[start..end], bytes - start) {
+                return Ok(val);
             }
         }
 
@@ -228,13 +226,13 @@ impl StaticHeader {
     pub fn determine_ownership<F>(f: &mut F) -> EngineResult<DevOwnership>
         where F: Read + Seek
     {
-        let (buf, _) = try!(StaticHeader::read_into_buf(f));
+        let (buf, bytes) = try!(StaticHeader::read_into_buf(f));
 
         // Using setup() as a test of ownership sets a high bar. It is
         // not sufficient to have STRAT_MAGIC to be considered "Ours",
         // it must also have correct CRC, no weird stuff in fields,
         // etc!
-        match StaticHeader::setup_from_buf(&buf) {
+        match StaticHeader::setup_from_buf(&buf, bytes) {
             Ok(Some(sh)) => Ok(DevOwnership::Ours(sh.pool_uuid)),
             Ok(None) => {
                 if buf.iter().any(|x| *x != 0) {