Added simplest device mount implementation (includes NullDevice and RandomDevice)

libraries/nacl-mounts/dev/DevMount.cc

Index: libraries/nacl-mounts/dev/DevMount.cc
===================================================================
--- libraries/nacl-mounts/dev/DevMount.cc	(revision 0)
+++ libraries/nacl-mounts/dev/DevMount.cc	(revision 0)
@@ -0,0 +1,92 @@
+/*
+ * Copyright (c) 2012 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "../dev/DevMount.h"
+#include <irt.h>
+#include <cstring>
+#include "../dev/NullDevice.h"
+#include "../dev/RandomDevice.h"
+
+DevMount::DevMount() {
+  max_inode = 0;
+  NullDevice* dev_null = new NullDevice();
+  Attach("/null", dev_null);
+  nacl_irt_random random;
+  if (nacl_interface_query(NACL_IRT_RANDOM_v0_1, &random, sizeof(random))) {
+    RandomDevice* dev_random = new RandomDevice(random.get_random_bytes);
+    Attach("/random", dev_random);
+  }
+}
+
+void DevMount::Attach(std::string path, Device* device) {
+  if (path_to_inode.find(path) == path_to_inode.end()) {
+    int inode = ++this->max_inode;
+    inode_to_path[inode] = path;
+    inode_to_dev[inode]  = device;
+    inode_to_ref[inode]  = 1;
+    path_to_inode[path]  = inode;
+  }
+}
+void DevMount::Ref(ino_t node) {
+  if (inode_to_path.find(node) != inode_to_path.end()) {
+    inode_to_ref[node]++;
+  }
+}
+void DevMount::Unref(ino_t node) {
+  if (inode_to_path.find(node) != inode_to_path.end()) {
+    inode_to_ref[node]--;

[Evgeniy Stepanov, 2012/05/11 10:47:34]

I suggest dropping all reference counting in DevMount (inode_to_ref, Ref,
Unref). It does not do anything in the current implementation, and it is not
needed for a static file system.

[vissi, 2012/05/11 11:49:19]

Done.

+  }
+}
+
+int DevMount::Creat(const std::string& path, mode_t mode, struct stat *buf) {

[Evgeniy Stepanov, 2012/05/11 10:47:34]

Missing return on one of the code paths.
This function is not needed anyway - you should not be able to create new files
in /dev.
Rename it to GetNode and handle the missing path case.

[vissi, 2012/05/11 11:49:19]

Done.

+  if (path_to_inode.find(path) != path_to_inode.end()) {
+    return Stat(path_to_inode[path], buf);
+  }
+}
+
+int DevMount::Stat(ino_t node, struct stat *buf) {
+  if (inode_to_path.find(node) == inode_to_path.end()) {
+    errno = EIO;

[Evgeniy Stepanov, 2012/05/11 10:47:34]

ENOENT

[vissi, 2012/05/11 11:49:19]

Done.

+    return -1;
+  }
+  memset(buf, 0, sizeof(struct stat));
+  buf->st_ino = node;
+  buf->st_mode = S_IFREG | 0777;
+  return 0;
+}
+
+int DevMount::Getdents(ino_t slot, off_t offset,

[Evgeniy Stepanov, 2012/05/11 10:47:34]

You don't have inodes for any directories, so this can not work, either. Just
drop it.

[vissi, 2012/05/11 11:49:19]

Should we be able to list existing devices? That's the only purpose for now.

[Evgeniy Stepanov, 2012/05/11 12:02:54]

Does it work this way? I suspect not. We need a test to figure it out.

Do we really need this functionality? It will complicate stuff a bit, we'll need
to allocate inodes for directories then (at least for "/").

+                       struct dirent *dir, unsigned int count) {
+  for (std::map<std::string, int>::const_iterator it = path_to_inode.begin();
+    it != path_to_inode.end(); ++it) {
+    memset(dir, 0, sizeof(struct dirent));
+    // We want d_ino to be non-zero because readdir()
+    // will return null if d_ino is zero.
+    dir->d_ino = 0x60061E;
+    dir->d_reclen = sizeof(struct dirent);
+    strncpy(dir->d_name, it->first.c_str(), sizeof(dir->d_name));
+  }
+  return 0;
+}
+
+ssize_t DevMount::Read(ino_t slot, off_t offset, void *buf, size_t count) {
+  if (inode_to_path.find(slot) != inode_to_path.end()) {
+    return inode_to_dev[slot]->Read(offset, buf, count);
+  } else {
+    errno = EIO;
+    return -1;
+  }
+}
+
+ssize_t DevMount::Write(ino_t slot, off_t offset, const void *buf,
+                        size_t count) {
+  if (inode_to_path.find(slot) != inode_to_path.end()) {
+    return inode_to_dev[slot]->Write(offset, buf, count);
+  } else {
+    errno = EIO;
+    return -1;
+  }
+}
+