fs: Initial VFS port

fs/anon.c

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: ISC
+
+// anonfs is a virtual file system. It backs files that don't live in any other
+// file system, like pipes or unbound sockets.
+
+#include <zinnia/atomic.h>
+#include <zinnia/vfs.h>
+
+static const struct vfs_super_block_ops anon_super_ops = {};
+
+static struct vfs_super_block anon_super = {
+    .rc = {.count = 1}, // There's always just this exact super block.
+    .ops = &anon_super_ops,
+};
+
+static const struct vfs_node_ops anon_node_ops = {};
+
+static _Atomic(ino_t) anon_inode_counter = 1;
+
+errno_t vfs_create_anon_inode(
+    const struct vfs_file_ops* file_ops,
+    enum vfs_node_type type,
+    mode_t mode,
+    const struct ident* identity,
+    struct vfs_node** out
+) {
+    struct vfs_node* node;
+    errno_t status = vfs_node_new(&anon_super, type, &anon_node_ops, mode, &node);
+    if (status)
+        return status;
+
+    node->file_ops = file_ops;
+    // Every anon node gets its own inode counter.
+    node->id = atomic_fetch_add(&anon_inode_counter, 1, ATOMIC_RELAXED);
+    node->uid = identity->euid;
+    node->gid = identity->egid;
+
+    *out = node;
+    return 0;
+}