When unmounting FAT volumes, close all open file handles and flush
buffers to disk

Return accurate counts of closed/released file handles and directories
in close_files, release_files, and release_dirs
---
 firmware/common/dir_uncached.c |    7 +++++--
 firmware/common/disk.c         |   22 ++++++++++++++--------
 firmware/common/file.c         |   31 +++++++++++++++++++++++++++++--
 firmware/include/file.h        |    1 +
 4 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/firmware/common/dir_uncached.c b/firmware/common/dir_uncached.c
index 00123c1..fd5df41 100644
--- a/firmware/common/dir_uncached.c
+++ b/firmware/common/dir_uncached.c
@@ -50,8 +50,11 @@ int release_dirs(int volume)
         (void)volume;
 #endif
         {
-            pdir->busy = false; /* mark as available, no further action */
-            closed++;
+            if (pdir->busy)
+            {
+                pdir->busy = false; /* mark as available, no further action */
+                closed++;
+            }
         }
     }
     return closed; /* return how many we did */
diff --git a/firmware/common/disk.c b/firmware/common/disk.c
index a23d51d..397b21b 100644
--- a/firmware/common/disk.c
+++ b/firmware/common/disk.c
@@ -263,19 +263,25 @@ int disk_unmount(int drive)
 
 int disk_unmount_all(void)
 {
-#ifndef HAVE_MULTIDRIVE
-    return disk_unmount(0);
-#else  /* HAVE_MULTIDRIVE */
     int unmounted = 0;
     int i;
-    for (i = 0; i < NUM_DRIVES; i++)
-    {
 #ifdef HAVE_HOTSWAP
-        if (storage_present(i))
+    mutex_lock(&disk_mutex);
 #endif
-            unmounted += disk_unmount(i);
+    for (i=0; i<NUM_VOLUMES; i++)
+    {
+        if(vol_drive[i] >= 0)
+        {
+            vol_drive[i] = -1; /* mark unused */
+            unmounted++;
+            close_files(i);
+            release_dirs(i);
+            fat_unmount(i, true);
+        }
     }
+#ifdef HAVE_HOTSWAP
+    mutex_unlock(&disk_mutex);
+#endif
 
     return unmounted;
-#endif  /* HAVE_MULTIDRIVE */
 }
diff --git a/firmware/common/file.c b/firmware/common/file.c
index 3477c10..9096587 100644
--- a/firmware/common/file.c
+++ b/firmware/common/file.c
@@ -807,8 +807,35 @@ int release_files(int volume)
         (void)volume;
 #endif
         {
-            pfile->busy = false; /* mark as available, no further action */
-            closed++;
+            if (pfile->busy)
+            {
+                pfile->busy = false; /* mark as available, no further action */
+                closed++;
+            }
+        }
+    }
+    return closed; /* return how many we did */
+}
+
+/* close all file handles on volume, flush dirty data */
+int close_files(int volume)
+{
+    struct filedesc* pfile = openfiles;
+    int fd;
+    int closed = 0;
+    for ( fd=0; fd<MAX_OPEN_FILES; fd++, pfile++)
+    {
+#ifdef HAVE_MULTIVOLUME
+        if (pfile->fatfile.volume == volume)
+#else
+        (void)volume;
+#endif
+        {
+            if (pfile->busy)
+            {
+                close(fd);
+                closed++;
+            }
         }
     }
     return closed; /* return how many we did */
diff --git a/firmware/include/file.h b/firmware/include/file.h
index ee52c3f..fc9aa32 100644
--- a/firmware/include/file.h
+++ b/firmware/include/file.h
@@ -101,6 +101,7 @@ extern int rename(const char* path, const char* newname);
 extern int ftruncate(int fd, off_t length);
 extern off_t filesize(int fd);
 extern int release_files(int volume);
+extern int close_files(int volume);
 int fdprintf (int fd, const char *fmt, ...) ATTRIBUTE_PRINTF(2, 3);
 #endif /* !CODEC && !PLUGIN */
 #endif
-- 
1.7.1