wut/libraries/wutdevoptab/devoptab_fs_read.c

#include "devoptab_fs.h"

ssize_t
__wut_fs_read(struct _reent *r,
              void *fd,
              char *ptr,
              size_t len)
{
   FSStatus status;
   FSCmdBlock cmd;
   uint8_t *alignedReadBuffer;
   uint32_t bytes, bytesRead;
   __wut_fs_file_t *file;

   if (!fd || !ptr) {
      r->_errno = EINVAL;
      return -1;
   }

   FSInitCmdBlock(&cmd);
   file = (__wut_fs_file_t *)fd;
   bytesRead = 0;

   // Check that the file was opened with read access
   if ((file->flags & O_ACCMODE) == O_WRONLY) {
      r->_errno = EBADF;
      return -1;
   }

   // Copy to internal buffer due to alignment requirement and read in chunks.
   alignedReadBuffer = memalign(0x40, 8192);
   while (len > 0) {
      size_t toRead = len > 8192 ? 8192 : len;

      // Write the data
      status = FSReadFile(__wut_devoptab_fs_client, &cmd, alignedReadBuffer, 1,
                          toRead, file->fd, 0, -1);
      if (status <= 0) {
         break;
      }

      // Copy to internal buffer
      bytes = (uint32_t)status;
      memcpy(ptr, alignedReadBuffer, bytes);

      file->offset += bytes;
      bytesRead    += bytes;
      ptr          += bytes;
      len          -= bytes;

      if (bytes < toRead) {
         // If we did not read the full requested toRead bytes then we reached
         // the end of the file.
         break;
      }
   }
   free(alignedReadBuffer);

   // Return partial read
   if (bytesRead > 0) {
      return bytesRead;
   }

   if (status < 0) {
      r->_errno = __wut_fs_translate_error(status);
      return -1;
   }

   return 0;
}