FileSystem: Get rid of VFS::absolute_path() and teach Mount about custodies.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/874bffc729a

Kernel/FileSystem/FileDescriptor.cpp

@@ -261,7 +261,7 @@ int FileDescriptor::close()
     return 0;
 }
 
-KResultOr<String> FileDescriptor::absolute_path()
+String FileDescriptor::absolute_path()
 {
     if (m_custody)
         return m_custody->absolute_path();

Kernel/FileSystem/FileDescriptor.h

@@ -43,7 +43,7 @@ public:
 
     ByteBuffer read_entire_file();
 
-    KResultOr<String> absolute_path();
+    String absolute_path();
 
     bool is_directory() const;
 

Kernel/FileSystem/InodeFile.cpp

@@ -41,12 +41,11 @@ KResultOr<Region*> InodeFile::mmap(Process& process, LinearAddress preferred_lad
     return region;
 }
 
-String InodeFile::absolute_path(FileDescriptor&) const
+String InodeFile::absolute_path(FileDescriptor& descriptor) const
 {
-    auto path_or_error = VFS::the().absolute_path(const_cast<Inode&>(inode()));
-    if (path_or_error.is_error())
-        return { };
-    return path_or_error.value();
+    ASSERT_NOT_REACHED();
+    ASSERT(descriptor.custody());
+    return descriptor.absolute_path();
 }
 
 KResult InodeFile::truncate(off_t size)

Kernel/FileSystem/ProcFS.cpp

@@ -192,10 +192,7 @@ ByteBuffer procfs$pid_fds(InodeIdentifier identifier)
         auto* descriptor = process.file_descriptor(i);
         if (!descriptor)
             continue;
-        auto result = descriptor->absolute_path();
-        if (result.is_error())
-            continue;
-        builder.appendf("% 3u %s\n", i, result.value().characters());
+        builder.appendf("% 3u %s\n", i, descriptor->absolute_path().characters());
     }
     return builder.to_byte_buffer();
 }
@@ -210,10 +207,7 @@ ByteBuffer procfs$pid_fd_entry(InodeIdentifier identifier)
     auto* descriptor = process.file_descriptor(fd);
     if (!descriptor)
         return { };
-    auto result = descriptor->absolute_path();
-    if (result.is_error())
-        return { };
-    return result.value().to_byte_buffer();
+    return descriptor->absolute_path().to_byte_buffer();
 }
 
 ByteBuffer procfs$pid_vm(InodeIdentifier identifier)
@@ -420,11 +414,7 @@ ByteBuffer procfs$mounts(InodeIdentifier)
         else {
             builder.appendf("%u:%u", mount.host().fsid(), mount.host().index());
             builder.append(' ');
-            auto result = VFS::the().absolute_path(mount.host());
-            if (result.is_error())
-                builder.append("[error]");
-            else
-                builder.append(result.value());
+            builder.append(mount.absolute_path());
         }
         builder.append('\n');
     });
@@ -442,15 +432,7 @@ ByteBuffer procfs$df(InodeIdentifier)
         builder.appendf("%u,", fs.free_block_count());
         builder.appendf("%u,", fs.total_inode_count());
         builder.appendf("%u,", fs.free_inode_count());
-        if (!mount.host().is_valid())
-            builder.append("/");
-        else {
-            auto result = VFS::the().absolute_path(mount.host());
-            if (result.is_error())
-                builder.append("[Error]");
-            else
-                builder.append(result.value());
-        }
+        builder.append(mount.absolute_path());
         builder.append('\n');
     });
     return builder.to_byte_buffer();
@@ -613,11 +595,7 @@ ByteBuffer procfs$inodes(InodeIdentifier)
     StringBuilder builder;
     for (auto it : all_inodes()) {
         RetainPtr<Inode> inode = *it;
-        auto result = VFS::the().absolute_path(*inode);
-        if (result.is_error())
-            continue;
-        auto path = result.value();
-        builder.appendf("Inode{K%x} %02u:%08u (%u) %s\n", inode.ptr(), inode->fsid(), inode->index(), inode->retain_count(), path.characters());
+        builder.appendf("Inode{K%x} %02u:%08u (%u)\n", inode.ptr(), inode->fsid(), inode->index(), inode->retain_count());
     }
     return builder.to_byte_buffer();
 }

Kernel/FileSystem/VirtualFileSystem.cpp

@@ -36,9 +36,8 @@ InodeIdentifier VFS::root_inode_id() const
     return m_root_inode->identifier();
 }
 
-bool VFS::mount(RetainPtr<FS>&& file_system, StringView path)
+bool VFS::mount(Retained<FS>&& file_system, StringView path)
 {
-    ASSERT(file_system);
     auto result = resolve_path_to_custody(path, root_custody());
     if (result.is_error()) {
         kprintf("VFS: mount can't resolve mount point '%s'\n", path.characters());
@@ -47,19 +46,19 @@ bool VFS::mount(RetainPtr<FS>&& file_system, StringView path)
     auto& inode = result.value()->inode();
     kprintf("VFS: mounting %s{%p} at %s (inode: %u)\n", file_system->class_name(), file_system.ptr(), path.characters(), inode.index());
     // FIXME: check that this is not already a mount point
-    auto mount = make<Mount>(inode.identifier(), move(file_system));
+    auto mount = make<Mount>(*result.value(), move(file_system));
     m_mounts.append(move(mount));
     return true;
 }
 
-bool VFS::mount_root(RetainPtr<FS>&& file_system)
+bool VFS::mount_root(Retained<FS>&& file_system)
 {
     if (m_root_inode) {
         kprintf("VFS: mount_root can't mount another root\n");
         return false;
     }
 
-    auto mount = make<Mount>(InodeIdentifier(), move(file_system));
+    auto mount = make<Mount>(nullptr, move(file_system));
 
     auto root_inode_id = mount->guest().fs()->root_inode();
     auto root_inode = mount->guest().fs()->get_inode(root_inode_id);
@@ -565,53 +564,6 @@ RetainPtr<Inode> VFS::get_inode(InodeIdentifier inode_id)
     return inode_id.fs()->get_inode(inode_id);
 }
 
-KResultOr<String> VFS::absolute_path(InodeIdentifier inode_id)
-{
-    auto inode = get_inode(inode_id);
-    if (!inode)
-        return KResult(-EIO);
-    return absolute_path(*inode);
-}
-
-KResultOr<String> VFS::absolute_path(Inode& core_inode)
-{
-    Vector<InodeIdentifier> lineage;
-    RetainPtr<Inode> inode = &core_inode;
-    while (inode->identifier() != root_inode_id()) {
-        if (auto* mount = find_mount_for_guest(inode->identifier()))
-            lineage.append(mount->host());
-        else
-            lineage.append(inode->identifier());
-
-        InodeIdentifier parent_id;
-        if (inode->is_directory()) {
-            auto result = resolve_path("..", inode->identifier());
-            if (result.is_error())
-                return result.error();
-            parent_id = result.value();
-        } else {
-            parent_id = inode->parent()->identifier();
-        }
-        if (!parent_id.is_valid())
-            return KResult(-EIO);
-        inode = get_inode(parent_id);
-    }
-    if (lineage.is_empty())
-        return "/";
-    lineage.append(root_inode_id());
-    StringBuilder builder;
-    for (size_t i = lineage.size() - 1; i >= 1; --i) {
-        auto& child = lineage[i - 1];
-        auto parent = lineage[i];
-        if (auto* mount = find_mount_for_host(parent))
-            parent = mount->guest();
-        builder.append('/');
-        auto parent_inode = get_inode(parent);
-        builder.append(parent_inode->reverse_lookup(child));
-    }
-    return builder.to_string();
-}
-
 KResultOr<InodeIdentifier> VFS::resolve_path(StringView path, InodeIdentifier base, int options, InodeIdentifier* parent_id)
 {
     if (path.is_empty())
@@ -701,13 +653,27 @@ KResultOr<InodeIdentifier> VFS::resolve_path(StringView path, InodeIdentifier ba
     return crumb_id;
 }
 
-VFS::Mount::Mount(InodeIdentifier host, RetainPtr<FS>&& guest_fs)
-    : m_host(host)
-    , m_guest(guest_fs->root_inode())
+VFS::Mount::Mount(RetainPtr<Custody>&& host_custody, Retained<FS>&& guest_fs)
+    : m_guest(guest_fs->root_inode())
     , m_guest_fs(move(guest_fs))
+    , m_host_custody(move(host_custody))
 {
 }
 
+String VFS::Mount::absolute_path() const
+{
+    if (!m_host_custody)
+        return "/";
+    return m_host_custody->absolute_path();
+}
+
+InodeIdentifier VFS::Mount::host() const
+{
+    if (!m_host_custody)
+        return { };
+    return m_host_custody->inode().identifier();
+}
+
 void VFS::register_device(Device& device)
 {
     m_devices.set(encoded_device(device.major(), device.minor()), &device);

Kernel/FileSystem/VirtualFileSystem.h

@@ -41,17 +41,20 @@ class VFS {
 public:
     class Mount {
     public:
-        Mount(InodeIdentifier host, RetainPtr<FS>&&);
+        Mount(RetainPtr<Custody>&&, Retained<FS>&&);
 
-        InodeIdentifier host() const { return m_host; }
+        InodeIdentifier host() const;
         InodeIdentifier guest() const { return m_guest; }
 
         const FS& guest_fs() const { return *m_guest_fs; }
 
+        String absolute_path() const;
+
     private:
         InodeIdentifier m_host;
         InodeIdentifier m_guest;
-        RetainPtr<FS> m_guest_fs;
+        Retained<FS> m_guest_fs;
+        RetainPtr<Custody> m_host_custody;
     };
 
     [[gnu::pure]] static VFS& the();
@@ -59,8 +62,8 @@ public:
     VFS();
     ~VFS();
 
-    bool mount_root(RetainPtr<FS>&&);
-    bool mount(RetainPtr<FS>&&, StringView path);
+    bool mount_root(Retained<FS>&&);
+    bool mount(Retained<FS>&&, StringView path);
 
     KResultOr<Retained<FileDescriptor>> open(RetainPtr<Device>&&, int options);
     KResultOr<Retained<FileDescriptor>> open(StringView path, int options, mode_t mode, Custody& base);
@@ -86,9 +89,6 @@ public:
     size_t mount_count() const { return m_mounts.size(); }
     void for_each_mount(Function<void(const Mount&)>) const;
 
-    KResultOr<String> absolute_path(Inode&);
-    KResultOr<String> absolute_path(InodeIdentifier);
-
     InodeIdentifier root_inode_id() const;
     Inode* root_inode() { return m_root_inode.ptr(); }
     const Inode* root_inode() const { return m_root_inode.ptr(); }