diff --git a/libraries/AP_Filesystem/AP_Filesystem.cpp b/libraries/AP_Filesystem/AP_Filesystem.cpp
index b7a1cf79af..262cc152c0 100644
--- a/libraries/AP_Filesystem/AP_Filesystem.cpp
+++ b/libraries/AP_Filesystem/AP_Filesystem.cpp
@@ -306,6 +306,24 @@ AP_Filesystem_Backend::FormatStatus AP_Filesystem::get_format_status(void) const
 #endif
 }
 
+
+// block filesystem access
+void AP_Filesystem::block_access(void)
+{
+    for (uint8_t i=0; i<ARRAY_SIZE(backends); i++) {
+        backends[i].fs.block_access();
+    }
+}
+
+// free filesystem access
+void AP_Filesystem::free_access(void)
+{
+    for (uint8_t i=0; i<ARRAY_SIZE(backends); i++) {
+        backends[i].fs.free_access();
+    }
+}
+
+
 namespace AP
 {
 AP_Filesystem &FS()
diff --git a/libraries/AP_Filesystem/AP_Filesystem.h b/libraries/AP_Filesystem/AP_Filesystem.h
index ac785bf30a..b2f0f14366 100644
--- a/libraries/AP_Filesystem/AP_Filesystem.h
+++ b/libraries/AP_Filesystem/AP_Filesystem.h
@@ -127,7 +127,14 @@ public:
       load a full file. Use delete to free the data
      */
     FileData *load_file(const char *filename);
-    
+
+
+    // block filesystem access
+    void block_access(void);
+
+    // free filesystem access
+    void free_access(void);
+
 private:
     struct Backend {
         const char *prefix;
diff --git a/libraries/AP_Filesystem/AP_Filesystem_FATFS.cpp b/libraries/AP_Filesystem/AP_Filesystem_FATFS.cpp
index 58b387b553..f5d242fada 100644
--- a/libraries/AP_Filesystem/AP_Filesystem_FATFS.cpp
+++ b/libraries/AP_Filesystem/AP_Filesystem_FATFS.cpp
@@ -36,7 +36,7 @@ static bool remount_needed;
 // use a semaphore to ensure that only one filesystem operation is
 // happening at a time. A recursive semaphore is used to cope with the
 // mkdir() inside sdcard_retry()
-static HAL_Semaphore sem;
+HAL_Semaphore AP_Filesystem_FATFS::sem;
 
 typedef struct {
     FIL *fh;
diff --git a/libraries/AP_Filesystem/AP_Filesystem_FATFS.h b/libraries/AP_Filesystem/AP_Filesystem_FATFS.h
index 7b6d51be8e..0e1956b7e7 100644
--- a/libraries/AP_Filesystem/AP_Filesystem_FATFS.h
+++ b/libraries/AP_Filesystem/AP_Filesystem_FATFS.h
@@ -55,9 +55,16 @@ public:
     bool format(void) override;
     AP_Filesystem_Backend::FormatStatus get_format_status() const override;
 
+    // block filesystem access
+    void block_access(void) override { sem.take_blocking(); }
+
+    // free filesystem access
+    void free_access(void) override { sem.give(); }
+
 private:
     void format_handler(void);
     FormatStatus format_status;
+    static HAL_Semaphore sem;
 };
 
 #endif  // #if AP_FILESYSTEM_FATFS_ENABLED
diff --git a/libraries/AP_Filesystem/AP_Filesystem_backend.h b/libraries/AP_Filesystem/AP_Filesystem_backend.h
index 187f9c48c3..f4c1ae58ff 100644
--- a/libraries/AP_Filesystem/AP_Filesystem_backend.h
+++ b/libraries/AP_Filesystem/AP_Filesystem_backend.h
@@ -94,6 +94,13 @@ public:
     // unload data from load_file()
     virtual void unload_file(FileData *fd);
 
+
+    // block filesystem access
+    virtual void block_access(void) {}
+
+    // free filesystem access
+    virtual void free_access(void) {}
+
 protected:
     // return true if file operations are allowed
     bool file_op_allowed(void) const;