fs/shmfs: implement read and write interface

To pass LTP posix case mmap/1-2.c

Signed-off-by: fangxinyong <fangxinyong@xiaomi.com>

fs/shm/shmfs.c

@@ -89,7 +89,45 @@ const struct file_operations g_shmfs_operations =
 static ssize_t shmfs_read(FAR struct file *filep, FAR char *buffer,
                           size_t buflen)
 {
-  return -ENOSYS;
+  FAR struct shmfs_object_s *sho;
+  ssize_t nread;
+  off_t startpos;
+  off_t endpos;
+
+  DEBUGASSERT(filep->f_inode != NULL && filep->f_inode->i_private != NULL);
+
+  sho = filep->f_inode->i_private;
+
+  if (filep->f_pos > sho->length)
+    {
+      return 0;
+    }
+
+  /* Handle attempts to read beyond the end of the file. */
+
+  startpos = filep->f_pos;
+  nread    = buflen;
+  endpos   = startpos + buflen;
+
+  if (endpos > sho->length)
+    {
+      endpos = sho->length;
+      nread  = endpos - startpos;
+    }
+
+  /* Copy data from the memory object to the user buffer */
+
+  if (sho->paddr != NULL)
+    {
+      memcpy(buffer, sho->paddr + startpos, nread);
+      filep->f_pos += nread;
+    }
+  else
+    {
+      DEBUGASSERT(sho->length == 0 && nread == 0);
+    }
+
+  return nread;
 }
 
 /****************************************************************************
@@ -99,7 +137,41 @@ static ssize_t shmfs_read(FAR struct file *filep, FAR char *buffer,
 static ssize_t shmfs_write(FAR struct file *filep, FAR const char *buffer,
                            size_t buflen)
 {
-  return -ENOSYS;
+  FAR struct shmfs_object_s *sho;
+  ssize_t nwritten;
+  off_t startpos;
+  off_t endpos;
+
+  DEBUGASSERT(filep->f_inode != NULL && filep->f_inode->i_private != NULL);
+
+  sho = filep->f_inode->i_private;
+
+  /* Handle attempts to write beyond the end of the file */
+
+  startpos = filep->f_pos;
+  nwritten = buflen;
+  endpos   = startpos + buflen;
+
+  /* Desn't support shm auto expand, truncate first */
+
+  if (endpos > sho->length)
+    {
+      return -EFBIG;
+    }
+
+  /* Copy data from the user buffer to the memory object */
+
+  if (sho->paddr != NULL)
+    {
+      memcpy(sho->paddr + startpos, buffer, nwritten);
+      filep->f_pos += nwritten;
+    }
+  else
+    {
+      DEBUGASSERT(sho->length == 0 && nwritten == 0);
+    }
+
+  return nwritten;
 }
 
 /****************************************************************************