Add mbed_file_handle lookup function

Add a necessary helper to allow FileHandle objects to be obtained
from POSIX file descriptors.

Primary envisaged use case is to act on STDIN_FILENO etc, eg to
set it non-blocking or use sigio, or to use the enable API.

platform/mbed_retarget.cpp

@@ -290,7 +290,7 @@ static FileHandle *get_console(int fd)
 }
 
 /* Deal with the fact C library may not _open descriptors 0, 1, 2 - auto bind */
-static FileHandle *get_fhc(int fd)
+FileHandle *mbed::mbed_file_handle(int fd)
 {
     if (fd >= OPEN_MAX) {
         return NULL;
@@ -490,13 +490,13 @@ extern "C" FILEHANDLE PREFIX(_open)(const char *name, int openflags)
     /* Use the posix convention that stdin,out,err are filehandles 0,1,2.
      */
     if (std::strcmp(name, __stdin_name) == 0) {
-        get_fhc(STDIN_FILENO);
+        mbed_file_handle(STDIN_FILENO);
         return STDIN_FILENO;
     } else if (std::strcmp(name, __stdout_name) == 0) {
-        get_fhc(STDOUT_FILENO);
+        mbed_file_handle(STDOUT_FILENO);
         return STDOUT_FILENO;
     } else if (std::strcmp(name, __stderr_name) == 0) {
-        get_fhc(STDERR_FILENO);
+        mbed_file_handle(STDERR_FILENO);
         return STDERR_FILENO;
     }
 #endif
@@ -555,7 +555,7 @@ extern "C" int PREFIX(_close)(FILEHANDLE fh)
 
 extern "C" int close(int fildes)
 {
-    FileHandle *fhc = get_fhc(fildes);
+    FileHandle *fhc = mbed_file_handle(fildes);
     filehandles[fildes] = NULL;
     if (fhc == NULL) {
         errno = EBADF;
@@ -667,7 +667,7 @@ finish:
 extern "C" ssize_t write(int fildes, const void *buf, size_t length)
 {
 
-    FileHandle *fhc = get_fhc(fildes);
+    FileHandle *fhc = mbed_file_handle(fildes);
     if (fhc == NULL) {
         errno = EBADF;
         return -1;
@@ -761,8 +761,7 @@ extern "C" int PREFIX(_read)(FILEHANDLE fh, unsigned char *buffer, unsigned int
 
 extern "C" ssize_t read(int fildes, void *buf, size_t length)
 {
-
+    FileHandle *fhc = mbed_file_handle(fildes);
-    FileHandle *fhc = get_fhc(fildes);
     if (fhc == NULL) {
         errno = EBADF;
         return -1;
@@ -789,7 +788,7 @@ extern "C" int _isatty(FILEHANDLE fh)
 
 extern "C" int isatty(int fildes)
 {
-    FileHandle *fhc = get_fhc(fildes);
+    FileHandle *fhc = mbed_file_handle(fildes);
     if (fhc == NULL) {
         errno = EBADF;
         return 0;
@@ -828,7 +827,7 @@ int _lseek(FILEHANDLE fh, int offset, int whence)
 
 extern "C" off_t lseek(int fildes, off_t offset, int whence)
 {
-    FileHandle *fhc = get_fhc(fildes);
+    FileHandle *fhc = mbed_file_handle(fildes);
     if (fhc == NULL) {
         errno = EBADF;
         return -1;
@@ -844,7 +843,7 @@ extern "C" off_t lseek(int fildes, off_t offset, int whence)
 
 extern "C" int ftruncate(int fildes, off_t length)
 {
-    FileHandle *fhc = get_fhc(fildes);
+    FileHandle *fhc = mbed_file_handle(fildes);
     if (fhc == NULL) {
         errno = EBADF;
         return -1;
@@ -868,7 +867,7 @@ extern "C" int PREFIX(_ensure)(FILEHANDLE fh)
 
 extern "C" int fsync(int fildes)
 {
-    FileHandle *fhc = get_fhc(fildes);
+    FileHandle *fhc = mbed_file_handle(fildes);
     if (fhc == NULL) {
         errno = EBADF;
         return -1;
@@ -886,7 +885,7 @@ extern "C" int fsync(int fildes)
 #ifdef __ARMCC_VERSION
 extern "C" long PREFIX(_flen)(FILEHANDLE fh)
 {
-    FileHandle *fhc = get_fhc(fh);
+    FileHandle *fhc = mbed_file_handle(fh);
     if (fhc == NULL) {
         errno = EBADF;
         return -1;
@@ -936,7 +935,7 @@ extern "C" int _fstat(int fh, struct stat *st)
 
 extern "C" int fstat(int fildes, struct stat *st)
 {
-    FileHandle *fhc = get_fhc(fildes);
+    FileHandle *fhc = mbed_file_handle(fildes);
     if (fhc == NULL) {
         errno = EBADF;
         return -1;
@@ -949,7 +948,7 @@ extern "C" int fstat(int fildes, struct stat *st)
 
 extern "C" int fcntl(int fildes, int cmd, ...)
 {
-    FileHandle *fhc = get_fhc(fildes);
+    FileHandle *fhc = mbed_file_handle(fildes);
     if (fhc == NULL) {
         errno = EBADF;
         return -1;
@@ -994,7 +993,7 @@ extern "C" int poll(struct pollfd fds[], nfds_t nfds, int timeout)
     for (nfds_t n = 0; n < nfds; n++) {
         // Underlying FileHandle poll returns POLLNVAL if given NULL, so
         // we don't need to take special action.
-        fhs[n].fh = get_fhc(fds[n].fd);
+        fhs[n].fh = mbed_file_handle(fds[n].fd);
         fhs[n].events = fds[n].events;
     }
     int ret = poll(fhs, nfds, timeout);

platform/mbed_retarget.h

@@ -133,6 +133,27 @@ FileHandle *mbed_target_override_console(int fd);
  */
 FileHandle *mbed_override_console(int fd);
 
+/** Look up the Mbed file handle corresponding to a file descriptor
+ *
+ * This conversion function permits an application to find the underlying
+ * FileHandle object corresponding to a POSIX file descriptor.
+ *
+ * This allows access to specialized behavior only available via the
+ * FileHandle API.
+ *
+ * Example of saving power by disabling console input - for buffered serial,
+ * this would release the RX interrupt handler, which would release the
+ * deep sleep lock.
+ * @code
+ * mbed_file_handle(STDIN_FILENO)->enable_input(false);
+ * @endcode
+ *
+ * @param fd file descriptor
+ * @return   FileHandle pointer
+ *           NULL if descriptor does not correspond to a FileHandle (only
+ *           possible if it's not open with current implementation).
+ */
+FileHandle *mbed_file_handle(int fd);
 }
 
 typedef mbed::DirHandle DIR;