Improve mmap storage error messages

Trying to map unusual Info's gave unhelpful messages.

diff --git a/storage/mmap.go b/storage/mmap.go
index 9120c6f3388efb7f4a5486bbd7004d97094b8d93..94603a8c436110ca6b56ff0700f481019b18d6d8 100644 (file)
--- a/storage/mmap.go
+++ b/storage/mmap.go
@@ -99,49 +99,56 @@ func mMapTorrent(md *metainfo.Info, location string) (mms mmap_span.MMapSpan, er
        }()
        for _, miFile := range md.UpvertedFiles() {
                fileName := filepath.Join(append([]string{location, md.Name}, miFile.Path...)...)
-               err = os.MkdirAll(filepath.Dir(fileName), 0777)
+               var mm mmap.MMap
+               mm, err = mmapFile(fileName, miFile.Length)
                if err != nil {
-                       err = fmt.Errorf("error creating data directory %q: %s", filepath.Dir(fileName), err)
+                       err = fmt.Errorf("file %q: %s", miFile.DisplayPath(md), err)
                        return
                }
-               var file *os.File
-               file, err = os.OpenFile(fileName, os.O_CREATE|os.O_RDWR, 0666)
-               if err != nil {
-                       return
-               }
-               func() {
-                       defer file.Close()
-                       var fi os.FileInfo
-                       fi, err = file.Stat()
-                       if err != nil {
-                               return
-                       }
-                       if fi.Size() < miFile.Length {
-                               err = file.Truncate(miFile.Length)
-                               if err != nil {
-                                       return
-                               }
-                       }
-                       if miFile.Length == 0 {
-                               // Can't mmap() regions with length 0.
-                               return
-                       }
-                       var mMap mmap.MMap
-                       mMap, err = mmap.MapRegion(file,
-                               int(miFile.Length), // Probably not great on <64 bit systems.
-                               mmap.RDWR, 0, 0)
-                       if err != nil {
-                               err = fmt.Errorf("error mapping file %q, length %d: %s", file.Name(), miFile.Length, err)
-                               return
-                       }
-                       if int64(len(mMap)) != miFile.Length {
-                               panic("mmap has wrong length")
-                       }
-                       mms.Append(mMap)
-               }()
+               mms.Append(mm)
+       }
+       return
+}
+
+func mmapFile(name string, size int64) (ret mmap.MMap, err error) {
+       dir := filepath.Dir(name)
+       err = os.MkdirAll(dir, 0777)
+       if err != nil {
+               err = fmt.Errorf("making directory %q: %s", dir, err)
+               return
+       }
+       var file *os.File
+       file, err = os.OpenFile(name, os.O_CREATE|os.O_RDWR, 0666)
+       if err != nil {
+               return
+       }
+       defer file.Close()
+       var fi os.FileInfo
+       fi, err = file.Stat()
+       if err != nil {
+               return
+       }
+       if fi.Size() < size {
+               // I think this is necessary on HFS+. Maybe Linux will SIGBUS too if
+               // you overmap a file but I'm not sure.
+               err = file.Truncate(size)
                if err != nil {
                        return
                }
        }
+       if size == 0 {
+               // Can't mmap() regions with length 0.
+               return
+       }
+       ret, err = mmap.MapRegion(file,
+               int(size), // Probably not great on <64 bit systems.
+               mmap.RDWR, 0, 0)
+       if err != nil {
+               err = fmt.Errorf("mapping file %q, length %d: %s", file.Name(), size, err)
+               return
+       }
+       if int64(len(ret)) != size {
+               panic("mmap has wrong length")
+       }
        return
 }