fs: implement FIFO file

kernel/fs/fifo.c

@@ -29,11 +29,19 @@ static int fifo_open(file_description* desc, mode_t mode) {
     (void)mode;
     if ((desc->flags & O_RDONLY) && (desc->flags & O_WRONLY))
         return -EINVAL;
+
     struct fifo* fifo = (struct fifo*)desc->inode;
     if (desc->flags & O_RDONLY)
         ++fifo->num_readers;
     if (desc->flags & O_WRONLY)
         ++fifo->num_writers;
+
+    if (desc->inode->dev == 0) {
+        // This is a fifo created by pipe syscall.
+        // We don't need to block here.
+        return 0;
+    }
+
     int rc = file_description_block(desc, open_should_unblock);
     if (rc == -EAGAIN && (desc->flags & O_WRONLY))
         return -ENXIO;

kernel/fs/fs.c

@@ -59,6 +59,8 @@ void inode_unref(struct inode* inode) {
 void inode_destroy(struct inode* inode) {
     ASSERT(inode->ref_count == 0 && inode->num_links == 0);
     ASSERT(inode->fops->destroy_inode);
+    inode_unref(inode->fifo);
+    inode_unref((struct inode*)inode->bound_socket);
     inode->fops->destroy_inode(inode);
 }
 

kernel/fs/fs.h

@@ -65,6 +65,7 @@ struct inode {
     file_ops* fops;
     dev_t dev;  // Device number of device containing this inode
     dev_t rdev; // Device number (if this inode is a special file)
+    _Atomic(struct inode*) fifo;
     _Atomic(unix_socket*) bound_socket;
     _Atomic(nlink_t) num_links;
     atomic_size_t ref_count;

kernel/fs/vfs.c

@@ -413,6 +413,31 @@ static struct inode* resolve_special_file(struct inode* inode) {
             return ERR_PTR(-ENODEV);
         return device;
     }
+
+    if (S_ISFIFO(inode->mode)) {
+        if (inode->fifo) {
+            struct inode* fifo = inode->fifo;
+            inode_ref(fifo);
+            inode_unref(inode);
+            return fifo;
+        }
+
+        struct inode* new_fifo = fifo_create();
+        if (IS_ERR(new_fifo))
+            return ERR_CAST(new_fifo);
+        new_fifo->dev = inode->dev; // Signal that this fifo is bound to a file
+        inode_ref(new_fifo);
+
+        struct inode* expected = NULL;
+        if (atomic_compare_exchange_strong(&inode->fifo, &expected, new_fifo)) {
+            inode_unref(inode);
+            return new_fifo;
+        }
+        inode_ref(expected);
+        inode_unref(new_fifo);
+        return expected;
+    }
+
     return inode;
 }