Implement /dev/null

fs/dev.c

@@ -8,14 +8,37 @@ struct dev_ops *block_devs[] = {
 };
 struct dev_ops *char_devs[] = {
     [0 ... 255] = NULL,
+    [1] = &null_dev,
     [4] = &tty_dev,
 };
 
 int dev_open(int major, int minor, int type, struct fd *fd) {
     struct dev_ops *dev = (type == DEV_BLOCK ? block_devs : char_devs)[major];
     if (dev == NULL)
-        return _ENODEV;
+        return _ENXIO;
     fd->ops = &dev->fd;
+    if (!dev->open)
+        return 0;
     return dev->open(major, minor, type, fd);
 }
 
+// this device seemed so simple it was hardly worth making a new file for it
+
+static int null_open(int major, int minor, int type, struct fd *fd) {
+    if (minor != 3)
+        return _ENXIO;
+    return 0;
+}
+static ssize_t null_read(struct fd *fd, void *buf, size_t bufsize) {
+    return 0;
+}
+static ssize_t null_write(struct fd *fd, const void *buf, size_t bufsize) {
+    return bufsize;
+}
+struct dev_ops null_dev = {
+    .open = null_open,
+    .fd = {
+        .read = null_read,
+        .write = null_write,
+    },
+};

fs/dev.h

@@ -43,4 +43,6 @@ extern struct dev_ops *char_devs[];
 
 int dev_open(int major, int minor, int type, struct fd *fd);
 
+extern struct dev_ops null_dev;
+
 #endif

fs/generic.c

@@ -54,7 +54,7 @@ struct fd *generic_openat(struct fd *at, const char *path_raw, int flags, int mo
         assert(!S_ISLNK(stat.mode));
         if (S_ISBLK(stat.mode) || S_ISCHR(stat.mode)) {
             int type;
-            if (stat.mode & S_IFBLK)
+            if (S_ISBLK(stat.mode))
                 type = DEV_BLOCK;
             else
                 type = DEV_CHAR;

kernel/fs.c

@@ -123,9 +123,11 @@ dword_t sys_close(fd_t f) {
     if (fd == NULL)
         return _EBADF;
     if (--fd->refcount == 0) {
-        int err = fd->ops->close(fd);
-        if (err < 0)
-            return err;
+        if (fd->ops->close) {
+            int err = fd->ops->close(fd);
+            if (err < 0)
+                return err;
+        }
         free(fd);
     }
     current->files[f] = NULL;