Kernel: Add a new fcntl() system call

kernel/include/sys/Syscall.h

@@ -16,6 +16,7 @@
 #define SYS_close 11
 #define SYS_seek 12
 #define SYS_exec 13
+#define SYS_fcntl 14
 
 namespace Syscall
 {
@@ -38,3 +39,4 @@ void sys_read(Context* context, int fd, size_t size, char* buffer);
 void sys_close(Context* context, int fd);
 void sys_seek(Context* context, int fd, long offset, int whence);
 void sys_exec(Context* context, const char* pathname);
+void sys_fcntl(Context* context, int fd, int command, uintptr_t arg);

kernel/include/thread/Task.h

@@ -46,6 +46,8 @@ struct Task
     Descriptor files[TASK_MAX_FDS];
 
     AddressSpace address_space;
+
+    int alloc_fd();
 };
 
 void set_context_from_task(Task& task, Context* ctx);

kernel/src/sys/Syscall.cpp

@@ -25,12 +25,13 @@ void Syscall::entry(Context* context)
     case SYS_close: sys_close(context, (int)context->rdi); break;
     case SYS_seek: sys_seek(context, (int)context->rdi, (long)context->rsi, (int)context->rdx); break;
     case SYS_exec: sys_exec(context, (const char*)context->rdi); break;
+    case SYS_fcntl: sys_fcntl(context, (int)context->rdi, (int)context->rsi, context->rdx); break;
     default: context->rax = -ENOSYS; break;
     }
     VMM::exit_syscall_context();
 }
 
-char* Syscall::strdup_from_user(const char* user_string)
+char* Syscall::strdup_from_user(const char* user_string) // FIXME: This function is a little hacky.
 {
     uint64_t phys = VMM::get_physical((uint64_t)user_string);
     if (phys == (uint64_t)-1) { return nullptr; }

kernel/src/sys/stdio.cpp

@@ -18,6 +18,42 @@
 #define SEEK_CUR 1
 #define SEEK_END 2
 
+#define FNCTL_DUPFD 0
+
+void sys_fcntl(Context* context, int fd, int command, uintptr_t arg)
+{
+    if (fd >= TASK_MAX_FDS || fd < 0)
+    {
+        context->rax = -EBADF;
+        return;
+    }
+    Task* current_task = Scheduler::current_task();
+    if (!current_task->files[fd].is_open())
+    {
+        context->rax = -EBADF;
+        return;
+    }
+    Descriptor& file = current_task->files[fd];
+    if (command == FNCTL_DUPFD)
+    {
+        int dupfd = current_task->alloc_fd();
+        if (dupfd < 0)
+        {
+            context->rax = -EMFILE;
+            return;
+        }
+        current_task->files[dupfd] = file;
+        context->rax = dupfd;
+        kdbgln("fcntl(F_DUPFD): duplicated fd %d, result is %d", fd, dupfd);
+        return;
+    }
+    else
+    {
+        context->rax = -EINVAL;
+        return;
+    }
+}
+
 void sys_seek(Context* context, int fd, long offset, int whence)
 {
     if (whence < SEEK_SET || whence > SEEK_END)
@@ -36,12 +72,13 @@ void sys_seek(Context* context, int fd, long offset, int whence)
         context->rax = -EBADF;
         return;
     }
+    Descriptor& file = current_task->files[fd];
     long new_offset;
     if (whence == SEEK_SET) new_offset = offset;
     else if (whence == SEEK_CUR)
-        new_offset = offset + current_task->files[fd].offset();
+        new_offset = offset + file.offset();
     else if (whence == SEEK_END)
-        new_offset = current_task->files[fd].length() + offset;
+        new_offset = file.length() + offset;
     else
         __builtin_unreachable();
     if (new_offset < 0)
@@ -49,7 +86,12 @@ void sys_seek(Context* context, int fd, long offset, int whence)
         context->rax = -EINVAL; // FIXME: Is this the right error?
         return;
     }
-    int result = current_task->files[fd].seek(new_offset);
+    if (new_offset == file.offset())
+    {
+        context->rax = new_offset;
+        return;
+    }
+    int result = file.seek(new_offset);
     if (result < 0)
     {
         context->rax = result;
@@ -77,12 +119,13 @@ void sys_write(Context* context, int fd, size_t size, const char* addr)
         context->rax = -EBADF;
         return;
     }
-    if (!current_task->files[fd].can_write())
+    Descriptor& file = current_task->files[fd];
+    if (!file.can_write())
     {
         context->rax = -EBADF;
         return;
     }
-    ssize_t result = current_task->files[fd].write(size, (const char*)VMM::get_physical((uint64_t)addr));
+    ssize_t result = file.write(size, (const char*)VMM::get_physical((uint64_t)addr));
     context->rax = (size_t)result;
     return;
 }
@@ -90,13 +133,8 @@ void sys_write(Context* context, int fd, size_t size, const char* addr)
 void sys_open(Context* context, const char* filename, int flags)
 {
     Task* current_task = Scheduler::current_task();
-    int fd;
+    int fd = current_task->alloc_fd();
-    for (fd = 0; fd < TASK_MAX_FDS; fd++)
+    if (fd < 0)
-    {
-        if (!current_task->files[fd].is_open()) break;
-    }
-
-    if (fd == TASK_MAX_FDS)
     {
         context->rax = -EMFILE;
         return;

kernel/src/thread/Task.cpp

@@ -27,3 +27,16 @@ bool Task::is_user_task()
 {
     return user_task;
 }
+
+int Task::alloc_fd()
+{
+    int fd;
+    for (fd = 0; fd < TASK_MAX_FDS; fd++)
+    {
+        if (!files[fd].is_open()) break;
+    }
+
+    if (fd == TASK_MAX_FDS) { return -1; }
+
+    return fd;
+}