Kernel+LibC: Add support for mount flags

At the moment, the actual flags are ignored, but we correctly propagate them all
the way from the original mount() syscall to each custody that resides on the
mounted FS.

Kernel/FileSystem/Custody.cpp

@@ -26,7 +26,7 @@ Custody* Custody::get_if_cached(Custody* parent, const StringView& name)
     return nullptr;
 }
 
-NonnullRefPtr<Custody> Custody::get_or_create(Custody* parent, const StringView& name, Inode& inode)
+NonnullRefPtr<Custody> Custody::get_or_create(Custody* parent, const StringView& name, Inode& inode, int mount_flags)
 {
     if (RefPtr<Custody> cached_custody = get_if_cached(parent, name)) {
         if (&cached_custody->inode() != &inode) {
@@ -35,13 +35,14 @@ NonnullRefPtr<Custody> Custody::get_or_create(Custody* parent, const StringView&
         ASSERT(&cached_custody->inode() == &inode);
         return *cached_custody;
     }
-    return create(parent, name, inode);
+    return create(parent, name, inode, mount_flags);
 }
 
-Custody::Custody(Custody* parent, const StringView& name, Inode& inode)
+Custody::Custody(Custody* parent, const StringView& name, Inode& inode, int mount_flags)
     : m_parent(parent)
     , m_name(name)
     , m_inode(inode)
+    , m_mount_flags(mount_flags)
 {
     LOCKER(all_custodies().lock());
     all_custodies().resource().append(this);

Kernel/FileSystem/Custody.h

@@ -1,10 +1,10 @@
 #pragma once
 
-#include <AK/String.h>
 #include <AK/Badge.h>
 #include <AK/InlineLinkedList.h>
 #include <AK/RefCounted.h>
 #include <AK/RefPtr.h>
+#include <AK/String.h>
 
 class Inode;
 class VFS;
@@ -15,10 +15,10 @@ class Custody : public RefCounted<Custody>
     , public InlineLinkedListNode<Custody> {
 public:
     static Custody* get_if_cached(Custody* parent, const StringView& name);
-    static NonnullRefPtr<Custody> get_or_create(Custody* parent, const StringView& name, Inode&);
+    static NonnullRefPtr<Custody> get_or_create(Custody* parent, const StringView& name, Inode&, int mount_flags);
-    static NonnullRefPtr<Custody> create(Custody* parent, const StringView& name, Inode& inode)
+    static NonnullRefPtr<Custody> create(Custody* parent, const StringView& name, Inode& inode, int mount_flags)
     {
-        return adopt(*new Custody(parent, name, inode));
+        return adopt(*new Custody(parent, name, inode, mount_flags));
     }
 
     ~Custody();
@@ -33,6 +33,8 @@ public:
     bool is_deleted() const { return m_deleted; }
     bool is_mounted_on() const { return m_mounted_on; }
 
+    int mount_flags() const { return m_mount_flags; }
+
     void did_delete(Badge<VFS>);
     void did_mount_on(Badge<VFS>);
     void did_rename(Badge<VFS>, const String& name);
@@ -42,11 +44,12 @@ public:
     Custody* m_prev { nullptr };
 
 private:
-    Custody(Custody* parent, const StringView& name, Inode&);
+    Custody(Custody* parent, const StringView& name, Inode&, int mount_flags);
 
     RefPtr<Custody> m_parent;
     String m_name;
     NonnullRefPtr<Inode> m_inode;
     bool m_deleted { false };
     bool m_mounted_on { false };
+    int m_mount_flags { 0 };
 };

Kernel/FileSystem/ProcFS.cpp

@@ -78,10 +78,10 @@ enum ProcFileType {
     FI_PID_stack,
     FI_PID_regs,
     FI_PID_fds,
-    FI_PID_exe, // symlink
+    FI_PID_exe,  // symlink
-    FI_PID_cwd, // symlink
+    FI_PID_cwd,  // symlink
     FI_PID_root, // symlink
-    FI_PID_fd,  // directory
+    FI_PID_fd,   // directory
     __FI_PID_End,
 
     FI_MaxStaticFileIndex,
@@ -651,6 +651,7 @@ Optional<KBuffer> procfs$df(InodeIdentifier)
         fs_object.add("mount_point", mount.absolute_path());
         fs_object.add("block_size", fs.block_size());
         fs_object.add("readonly", fs.is_readonly());
+        fs_object.add("mount_flags", mount.flags());
 
         if (fs.is_disk_backed())
             fs_object.add("device", static_cast<const DiskBackedFS&>(fs).device().absolute_path());

Kernel/FileSystem/VirtualFileSystem.cpp

@@ -38,12 +38,12 @@ InodeIdentifier VFS::root_inode_id() const
     return m_root_inode->identifier();
 }
 
-KResult VFS::mount(FS& file_system, Custody& mount_point)
+KResult VFS::mount(FS& file_system, Custody& mount_point, int flags)
 {
     auto& inode = mount_point.inode();
-    dbg() << "VFS: Mounting " << file_system.class_name() << " at " << mount_point.absolute_path() << " (inode: " << inode.identifier() << ")";
+    dbg() << "VFS: Mounting " << file_system.class_name() << " at " << mount_point.absolute_path() << " (inode: " << inode.identifier() << ") with flags " << flags;
     // FIXME: check that this is not already a mount point
-    Mount mount { file_system, &mount_point };
+    Mount mount { file_system, &mount_point, flags };
     m_mounts.append(move(mount));
     mount_point.did_mount_on({});
     return KSuccess;
@@ -79,7 +79,7 @@ bool VFS::mount_root(FS& file_system)
         return false;
     }
 
-    Mount mount { file_system, nullptr };
+    Mount mount { file_system, nullptr, 0 };
 
     auto root_inode_id = mount.guest().fs()->root_inode();
     auto root_inode = mount.guest().fs()->get_inode(root_inode_id);
@@ -283,7 +283,7 @@ KResultOr<NonnullRefPtr<FileDescription>> VFS::create(StringView path, int optio
     if (!new_file)
         return KResult(error);
 
-    auto new_custody = Custody::create(&parent_custody, p.basename(), *new_file);
+    auto new_custody = Custody::create(&parent_custody, p.basename(), *new_file, parent_custody.mount_flags());
     return FileDescription::create(*new_custody);
 }
 
@@ -603,10 +603,11 @@ RefPtr<Inode> VFS::get_inode(InodeIdentifier inode_id)
     return inode_id.fs()->get_inode(inode_id);
 }
 
-VFS::Mount::Mount(FS& guest_fs, Custody* host_custody)
+VFS::Mount::Mount(FS& guest_fs, Custody* host_custody, int flags)
     : m_guest(guest_fs.root_inode())
     , m_guest_fs(guest_fs)
     , m_host_custody(host_custody)
+    , m_flags(flags)
 {
 }
 
@@ -639,7 +640,7 @@ void VFS::sync()
 Custody& VFS::root_custody()
 {
     if (!m_root_custody)
-        m_root_custody = Custody::create(nullptr, "", *m_root_inode);
+        m_root_custody = Custody::create(nullptr, "", *m_root_inode, 0);
     return *m_root_custody;
 }
 
@@ -674,6 +675,8 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
     if (parent_custody)
         *parent_custody = custody_chain.last();
 
+    int mount_flags = custody_chain.last().mount_flags();
+
     for (int i = 0; i < parts.size(); ++i) {
         bool inode_was_root_at_head_of_loop = current_root.inode().identifier() == crumb_id;
         auto crumb_inode = get_inode(crumb_id);
@@ -704,8 +707,10 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
             }
             return KResult(-ENOENT);
         }
-        if (auto mount = find_mount_for_host(crumb_id))
+        if (auto mount = find_mount_for_host(crumb_id)) {
             crumb_id = mount->guest();
+            mount_flags = mount->flags();
+        }
         if (inode_was_root_at_head_of_loop && crumb_id.is_root_inode() && crumb_id != current_root.inode().identifier() && part == "..") {
             auto mount = find_mount_for_guest(crumb_id);
             auto dir_inode = get_inode(mount->host());
@@ -715,7 +720,7 @@ KResultOr<NonnullRefPtr<Custody>> VFS::resolve_path(StringView path, Custody& ba
         crumb_inode = get_inode(crumb_id);
         ASSERT(crumb_inode);
 
-        custody_chain.append(Custody::create(&custody_chain.last(), part, *crumb_inode));
+        custody_chain.append(Custody::create(&custody_chain.last(), part, *crumb_inode, mount_flags));
 
         metadata = crumb_inode->metadata();
         if (metadata.is_directory()) {

Kernel/FileSystem/VirtualFileSystem.h

@@ -1,12 +1,12 @@
 #pragma once
 
-#include <AK/String.h>
 #include <AK/Badge.h>
 #include <AK/Function.h>
 #include <AK/HashMap.h>
 #include <AK/NonnullOwnPtrVector.h>
 #include <AK/OwnPtr.h>
 #include <AK/RefPtr.h>
+#include <AK/String.h>
 #include <Kernel/FileSystem/FileSystem.h>
 #include <Kernel/FileSystem/InodeIdentifier.h>
 #include <Kernel/FileSystem/InodeMetadata.h>
@@ -41,7 +41,7 @@ class VFS {
 public:
     class Mount {
     public:
-        Mount(FS&, Custody* host_custody);
+        Mount(FS&, Custody* host_custody, int flags);
 
         InodeIdentifier host() const;
         InodeIdentifier guest() const { return m_guest; }
@@ -50,11 +50,14 @@ public:
 
         String absolute_path() const;
 
+        int flags() const { return m_flags; }
+
     private:
         InodeIdentifier m_host;
         InodeIdentifier m_guest;
         NonnullRefPtr<FS> m_guest_fs;
         RefPtr<Custody> m_host_custody;
+        int m_flags;
     };
 
     static VFS& the();
@@ -63,7 +66,7 @@ public:
     ~VFS();
 
     bool mount_root(FS&);
-    KResult mount(FS&, Custody& mount_point);
+    KResult mount(FS&, Custody& mount_point, int flags);
     KResult unmount(InodeIdentifier guest_inode_id);
 
     KResultOr<NonnullRefPtr<FileDescription>> open(StringView path, int options, mode_t mode, Custody& base, Optional<UidAndGid> = {});

Kernel/Process.cpp

@@ -3642,7 +3642,7 @@ int Process::sys$mount(const Syscall::SC_mount_params* user_params)
         return -ENODEV;
     }
 
-    auto result = VFS::the().mount(fs.release_nonnull(), target_custody);
+    auto result = VFS::the().mount(fs.release_nonnull(), target_custody, params.flags);
     dbg() << "mount: successfully mounted " << source << " on " << target;
     return result;
 }
@@ -4170,8 +4170,9 @@ int Process::sys$chroot(const char* user_path, size_t path_length)
     auto directory_or_error = VFS::the().open_directory(path.value(), current_directory());
     if (directory_or_error.is_error())
         return directory_or_error.error();
-    m_root_directory_for_procfs = directory_or_error.value();
+    auto directory = directory_or_error.value();
-    set_root_directory(Custody::create(nullptr, "", directory_or_error.value()->inode()));
+    m_root_directory_for_procfs = directory;
+    set_root_directory(Custody::create(nullptr, "", directory->inode(), directory->mount_flags()));
     return 0;
 }
 

Kernel/Syscall.h

@@ -332,9 +332,9 @@ struct SC_link_params {
 };
 
 struct SC_chown_params {
-     StringArgument path;
+    StringArgument path;
-     u32 uid;
+    u32 uid;
-     u32 gid;
+    u32 gid;
 };
 
 struct SC_mknod_params {
@@ -357,6 +357,7 @@ struct SC_mount_params {
     StringArgument source;
     StringArgument target;
     StringArgument fs_type;
+    int flags;
 };
 
 void initialize();

Libraries/LibC/unistd.cpp

@@ -610,13 +610,18 @@ int reboot()
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
-int mount(const char* source, const char* target, const char* fs_type)
+int mount(const char* source, const char* target, const char* fs_type, int flags)
 {
     if (!source || !target || !fs_type) {
         errno = EFAULT;
         return -1;
     }
-    Syscall::SC_mount_params params { { source, strlen(source) }, { target, strlen(target) }, { fs_type, strlen(fs_type) } };
+    Syscall::SC_mount_params params {
+        { source, strlen(source) },
+        { target, strlen(target) },
+        { fs_type, strlen(fs_type) },
+        flags
+    };
     int rc = syscall(SC_mount, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }

Libraries/LibC/unistd.h

@@ -111,7 +111,7 @@ int fchown(int fd, uid_t, gid_t);
 int ftruncate(int fd, off_t length);
 int halt();
 int reboot();
-int mount(const char* source, const char* target, const char* fs_type);
+int mount(const char* source, const char* target, const char* fs_type, int flags);
 int umount(const char* mountpoint);
 
 enum {

Userland/mount.cpp

@@ -45,7 +45,7 @@ bool mount_all()
 
         dbg() << "Mounting " << devname << "(" << fstype << ")"
               << " on " << mountpoint;
-        int rc = mount(devname, mountpoint, fstype);
+        int rc = mount(devname, mountpoint, fstype, 0);
         if (rc != 0) {
             fprintf(stderr, "Failed to mount %s (%s) on %s: %s\n", devname, fstype, mountpoint, strerror(errno));
             all_ok = false;
@@ -101,7 +101,7 @@ int main(int argc, char** argv)
         String mountpoint = args.get_single_values()[1];
         String fstype = args.is_present("t") ? args.get("t") : "ext2";
 
-        if (mount(devname.characters(), mountpoint.characters(), fstype.characters()) < 0) {
+        if (mount(devname.characters(), mountpoint.characters(), fstype.characters(), 0) < 0) {
             perror("mount");
             return 1;
         }