Add FileHandle::truncate and ftruncate

Add support for file truncation (or extension) to the abstract API.

No hooks to actual implementations in this commit.

Author: kjbracey

platform/FileHandle.h

@@ -138,6 +138,21 @@ class FileHandle : private NonCopyable<FileHandle> {
      */
     virtual off_t size();
 
+    /** Truncate or extend a file.
+     *
+     * The file's length is set to the specified value. The seek pointer is
+     * not changed. If the file is extended, the extended area appears as if
+     * it were zero-filled.
+     *
+     *  @param length   The requested new length for the file
+     *
+     *  @return         Zero on success, negative error code on failure
+     */
+    virtual int truncate(off_t length)
+    {
+        return -EINVAL;
+    }
+
     /** Move the file position to a given offset from a given location.
      *
      *  @param offset The offset from whence to move to

platform/mbed_retarget.cpp

@@ -842,6 +842,23 @@ extern "C" off_t lseek(int fildes, off_t offset, int whence)
     return off;
 }
 
+extern "C" int ftruncate(int fildes, off_t length)
+{
+    FileHandle *fhc = get_fhc(fildes);
+    if (fhc == NULL) {
+        errno = EBADF;
+        return -1;
+    }
+
+    int err = fhc->truncate(length);
+    if (err < 0) {
+        errno = -err;
+        return -1;
+    } else {
+        return 0;
+    }
+}
+
 #ifdef __ARMCC_VERSION
 extern "C" int PREFIX(_ensure)(FILEHANDLE fh)
 {

platform/mbed_retarget.h

@@ -524,6 +524,7 @@ extern "C" {
     ssize_t write(int fildes, const void *buf, size_t nbyte);
     ssize_t read(int fildes, void *buf, size_t nbyte);
     off_t lseek(int fildes, off_t offset, int whence);
+    int ftruncate(int fildes, off_t length);
     int isatty(int fildes);
     int fsync(int fildes);
     int fstat(int fildes, struct stat *st);