Kernel+LibCore+LibC: Split the mount syscall into multiple syscalls

This is a preparation before we can create a usable mechanism to use
filesystem-specific mount flags.
To keep some compatibility with userland code, LibC and LibCore mount
functions are kept being usable, but now instead of doing an "atomic"
syscall, they do multiple syscalls to perform the complete procedure of
mounting a filesystem.

The FileBackedFileSystem IntrusiveList in the VFS code is now changed to
be protected by a Mutex, because when we mount a new filesystem, we need
to check if a filesystem is already created for a given source_fd so we
do a scan for that OpenFileDescription in that list. If we fail to find
an already-created filesystem we create a new one and register it in the
list if we successfully mounted it. We use a Mutex because we might need
to initiate disk access during the filesystem creation, which will take
other mutexes in other parts of the kernel, therefore making it not
possible to take a spinlock while doing this.

Userland/DevTools/UserspaceEmulator/Emulator.h

@@ -147,6 +147,7 @@ private:
     int virt$anon_create(size_t, int);
     int virt$beep();
     int virt$bind(int sockfd, FlatPtr address, socklen_t address_length);
+    u32 virt$bindmount(u32 params_addr);
     int virt$chdir(FlatPtr, size_t);
     int virt$chmod(FlatPtr);
     int virt$chown(FlatPtr);
@@ -167,6 +168,8 @@ private:
     int virt$fchown(int, uid_t, gid_t);
     u32 virt$fcntl(int fd, int, u32);
     int virt$fork();
+    u32 virt$fsopen(u32);
+    u32 virt$fsmount(u32);
     int virt$fstat(int, FlatPtr);
     int virt$ftruncate(int fd, FlatPtr length_addr);
     int virt$futex(FlatPtr);
@@ -199,7 +202,6 @@ private:
     u32 virt$madvise(FlatPtr, size_t, int);
     int virt$mkdir(FlatPtr path, size_t path_length, mode_t mode);
     u32 virt$mmap(u32);
-    u32 virt$mount(u32);
     u32 virt$mprotect(FlatPtr, size_t, int);
     FlatPtr virt$mremap(FlatPtr);
     int virt$annotate_mapping(FlatPtr);
@@ -219,6 +221,7 @@ private:
     int virt$recvfd(int, int);
     int virt$recvmsg(int sockfd, FlatPtr msg_addr, int flags);
     int virt$rename(FlatPtr address);
+    u32 virt$remount(u32);
     int virt$rmdir(FlatPtr path, size_t path_length);
     int virt$scheduler_get_parameters(FlatPtr);
     int virt$scheduler_set_parameters(FlatPtr);

Userland/DevTools/UserspaceEmulator/Emulator_syscalls.cpp

@@ -51,6 +51,8 @@ u32 Emulator::virt_syscall(u32 function, u32 arg1, u32 arg2, u32 arg3)
         return virt$beep();
     case SC_bind:
         return virt$bind(arg1, arg2, arg3);
+    case SC_bindmount:
+        return virt$bindmount(arg1);
     case SC_chdir:
         return virt$chdir(arg1, arg2);
     case SC_chmod:
@@ -94,6 +96,10 @@ u32 Emulator::virt_syscall(u32 function, u32 arg1, u32 arg2, u32 arg3)
         return virt$fork();
     case SC_fstat:
         return virt$fstat(arg1, arg2);
+    case SC_fsmount:
+        return virt$fsopen(arg1);
+    case SC_fsopen:
+        return virt$fsopen(arg1);
     case SC_ftruncate:
         return virt$ftruncate(arg1, arg2);
     case SC_futex:
@@ -158,8 +164,6 @@ u32 Emulator::virt_syscall(u32 function, u32 arg1, u32 arg2, u32 arg3)
         return virt$mkdir(arg1, arg2, arg3);
     case SC_mmap:
         return virt$mmap(arg1);
-    case SC_mount:
-        return virt$mount(arg1);
     case SC_mprotect:
         return virt$mprotect(arg1, arg2, arg3);
     case SC_mremap:
@@ -196,6 +200,8 @@ u32 Emulator::virt_syscall(u32 function, u32 arg1, u32 arg2, u32 arg3)
         return virt$recvmsg(arg1, arg2, arg3);
     case SC_rename:
         return virt$rename(arg1);
+    case SC_remount:
+        return virt$remount(arg1);
     case SC_rmdir:
         return virt$rmdir(arg1, arg2);
     case SC_scheduler_get_parameters:
@@ -906,18 +912,48 @@ FlatPtr Emulator::virt$mremap(FlatPtr params_addr)
     return -EINVAL;
 }
 
-u32 Emulator::virt$mount(u32 params_addr)
+u32 Emulator::virt$bindmount(u32 params_addr)
 {
-    Syscall::SC_mount_params params;
+    Syscall::SC_bindmount_params params;
     mmu().copy_from_vm(&params, params_addr, sizeof(params));
     auto target = mmu().copy_buffer_from_vm((FlatPtr)params.target.characters, params.target.length);
-    auto fs_path = mmu().copy_buffer_from_vm((FlatPtr)params.fs_type.characters, params.fs_type.length);
-    params.fs_type.characters = (char*)fs_path.data();
-    params.fs_type.length = fs_path.size();
     params.target.characters = (char*)target.data();
     params.target.length = target.size();
 
-    return syscall(SC_mount, &params);
+    return syscall(SC_bindmount, &params);
+}
+
+u32 Emulator::virt$remount(u32 params_addr)
+{
+    Syscall::SC_remount_params params;
+    mmu().copy_from_vm(&params, params_addr, sizeof(params));
+    auto target = mmu().copy_buffer_from_vm((FlatPtr)params.target.characters, params.target.length);
+    params.target.characters = (char*)target.data();
+    params.target.length = target.size();
+
+    return syscall(SC_remount, &params);
+}
+
+u32 Emulator::virt$fsopen(u32 params_addr)
+{
+    Syscall::SC_fsopen_params params;
+    mmu().copy_from_vm(&params, params_addr, sizeof(params));
+    auto fs_type = mmu().copy_buffer_from_vm((FlatPtr)params.fs_type.characters, params.fs_type.length);
+    params.fs_type.characters = (char*)fs_type.data();
+    params.fs_type.length = fs_type.size();
+
+    return syscall(SC_fsopen, &params);
+}
+
+u32 Emulator::virt$fsmount(u32 params_addr)
+{
+    Syscall::SC_fsmount_params params;
+    mmu().copy_from_vm(&params, params_addr, sizeof(params));
+    auto target = mmu().copy_buffer_from_vm((FlatPtr)params.target.characters, params.target.length);
+    params.target.characters = (char*)target.data();
+    params.target.length = target.size();
+
+    return syscall(SC_fsmount, &params);
 }
 
 u32 Emulator::virt$gettid()