Kernel, libc: Add dup2()

apps/src/init.c

@@ -63,6 +63,6 @@ int main()
         {
             msleep(100);
         }
-        if (result == child) { return 0; }
+        if (result == child) return 0;
     }
 }

apps/src/sh.c

@@ -186,7 +186,7 @@ int main()
                 perror("getchar");
                 return 1;
             }
-            if (feof(stdin)) { return 0; }
+            if (feof(stdin)) return 0;
             assert(false); // we should never get here
         }
         command_concat_char(&shell_command, (char)c);

kernel/include/sys/Syscall.h

@@ -26,6 +26,7 @@
 #define SYS_pstat 21
 #define SYS_getdents 22
 #define SYS_stat 23
+#define SYS_dup2 24
 
 struct stat;
 struct pstat;
@@ -59,4 +60,5 @@ void sys_access(Context* context, const char* path, int amode);
 void sys_fstat(Context* context, int fd, struct stat* buf);
 void sys_pstat(Context* context, long pid, struct pstat* buf);
 void sys_getdents(Context* context, int fd, struct luna_dirent* buf, size_t count);
-void sys_stat(Context* context, const char* path, struct stat* buf);
+void sys_stat(Context* context, const char* path, struct stat* buf);
+void sys_dup2(Context* context, int fd, int fd2);

kernel/src/sys/Syscall.cpp

@@ -36,6 +36,7 @@ void Syscall::entry(Context* context)
     case SYS_getdents:
         sys_getdents(context, (int)context->rdi, (struct luna_dirent*)context->rsi, (size_t)context->rdx);
         break;
+    case SYS_dup2: sys_dup2(context, (int)context->rdi, (int)context->rsi); break;
     default: context->rax = -ENOSYS; break;
     }
     VMM::exit_syscall_context();

kernel/src/sys/stdio.cpp

@@ -201,7 +201,7 @@ void sys_read(Context* context, int fd, size_t size, char* buffer)
     }
     int err;
     Descriptor* file = Scheduler::current_task()->descriptor_from_fd(fd, err);
-    if (!err)
+    if (!file)
     {
         context->rax = -err;
         return;
@@ -270,4 +270,30 @@ void sys_access(Context* context, const char* path, int) // FIXME: Use the amode
     else
         context->rax = 0;
     kfree(kpath);
+}
+
+void sys_dup2(Context* context, int fd, int fd2)
+{
+    int err;
+    Descriptor* file1 = Scheduler::current_task()->descriptor_from_fd(fd, err);
+    if (!file1)
+    {
+        context->rax = -err;
+        return;
+    }
+    if (!file1->is_open())
+    {
+        context->rax = -EBADF;
+        return;
+    }
+    Descriptor* file2 = Scheduler::current_task()->descriptor_from_fd(fd2, err);
+    if (!file2)
+    {
+        context->rax = -err;
+        return;
+    }
+    if (file2->is_open()) file2->close();
+    *file2 = *file1;
+    kinfoln("dup2(): overwrote fd %d with fd %d", fd2, fd);
+    context->rax = fd2;
 }

libs/libc/include/sys/syscall.h

@@ -25,5 +25,6 @@
 #define SYS_pstat 21
 #define SYS_getdents 22
 #define SYS_stat 23
+#define SYS_dup2 24
 
 #endif

libs/libc/include/unistd.h

@@ -63,6 +63,9 @@ extern "C"
     /* Returns a copy of the file descriptor fd. */
     int dup(int fd);
 
+    /* Causes the file descriptor fd2 to refer to the file descriptor fd. */
+    int dup2(int fd, int fd2);
+
     /* Checks if the current program can access the file or directory at path. */
     int access(const char* path, int amode);
 

libs/libc/src/syscall.cpp

@@ -25,6 +25,7 @@ extern "C" long syscall(long number, ...)
     case SYS_access:
     case SYS_fstat:
     case SYS_stat:
+    case SYS_dup2:
     case SYS_pstat:
     case SYS_open: {
         arg arg0 = va_arg(ap, arg);

libs/libc/src/unistd.cpp

@@ -73,6 +73,11 @@ extern "C"
         return fcntl(fd, F_DUPFD, 0);
     }
 
+    int dup2(int fd, int fd2)
+    {
+        return (int)syscall(SYS_dup2, fd, fd2);
+    }
+
     int access(const char* path, int amode)
     {
         return (int)syscall(SYS_access, path, amode);