From 817328f03f78eb5a2853411d64b411c67b9f63f7 Mon Sep 17 00:00:00 2001
From: Jake Hillion <jake@hillion.co.uk>
Date: Mon, 13 Dec 2021 13:33:22 +0000
Subject: [PATCH] fork/join copying

---
 examples/cp/Makefile    |   5 +-
 examples/cp/cp_cgroup.c | 144 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 148 insertions(+), 1 deletion(-)
 create mode 100644 examples/cp/cp_cgroup.c

diff --git a/examples/cp/Makefile b/examples/cp/Makefile
index 7b2a56c..c67ab5e 100644
--- a/examples/cp/Makefile
+++ b/examples/cp/Makefile
@@ -1,6 +1,6 @@
 C=clang
 
-all: c ml
+all: c c_cgroup ml
 
 clean:
 	rm -f c ml
@@ -8,6 +8,9 @@ clean:
 c: cp.c
 	${C} -o c cp.c
 
+c_cgroup: cp_cgroup.c
+	${C} -o c_cgroup cp_cgroup.c
+
 ml: cp.ml
 	opam switch default
 	ocamlopt -o ml cp.ml
diff --git a/examples/cp/cp_cgroup.c b/examples/cp/cp_cgroup.c
new file mode 100644
index 0000000..977209f
--- /dev/null
+++ b/examples/cp/cp_cgroup.c
@@ -0,0 +1,144 @@
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define IO_BLOCK_SIZE 4096
+
+/*
+ * Get size of regular file or error otherwise.
+ */
+off_t get_file_size(int fd) {
+  struct stat st;
+
+  if (fstat(fd, &st) < 0) {
+    perror("fstat");
+    return -1;
+  }
+
+  if (S_ISREG(st.st_mode)) {
+    return st.st_size;
+  } else {
+    return -1;
+  }
+}
+
+/*
+ * Move self to a leaf node of the cgroup.
+ */
+int leaf_self() {}
+
+/*
+ * Perform the copy between the two file descriptors.
+ */
+int copy(int src_fd, int dst_fd) {
+  off_t src_len;
+
+  int passwd_fd;
+  if ((passwd_fd = open("/home/jake/plot", O_RDONLY)) == -1) {
+    perror("open 2");
+    return 1;
+  } else {
+    // TODO: Debug this
+    fprintf(stderr, "opened second file successfully\n");
+  }
+
+  if ((src_len = get_file_size(src_fd)) == -1) {
+    return 1;
+  }
+
+  char buf[IO_BLOCK_SIZE];
+  off_t blocks =
+      (src_len / IO_BLOCK_SIZE) + ((src_len % IO_BLOCK_SIZE) > 0 ? 1 : 0);
+
+  for (off_t i = 0; i < blocks; i++) {
+    off_t len;
+    if (i == blocks - 1 && src_len % IO_BLOCK_SIZE != 0) {
+      len = src_len % IO_BLOCK_SIZE;
+    } else {
+      len = IO_BLOCK_SIZE;
+    }
+
+    if (read(src_fd, &buf, len) == -1) {
+      perror("read");
+      return -1;
+    };
+    if (write(dst_fd, &buf, len) == -1) {
+      perror("write");
+      return -1;
+    }
+  }
+
+  return 0;
+}
+
+int main(int argc, char **argv) {
+  if (argc != 3) {
+    fprintf(stderr, "usage: %s <src> <dst>\n", argv[0]);
+    return 1;
+  }
+
+  int src_fd, dst_fd;
+
+  if ((src_fd = open(argv[1], O_RDONLY)) == -1) {
+    perror("open");
+    return 1;
+  }
+  if ((dst_fd = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0666)) == -1) {
+    perror("open");
+    return 1;
+  }
+
+  // all necessary files opened, drop filesystem
+  // if (unshare(CLONE_FS) == -1) {
+  //   perror("unshare");
+  //   return -1;
+  // }
+
+  // fork and copy in a second process
+  pid_t child_pid = fork();
+  if (child_pid == -1) {
+    perror("fork");
+    return -1;
+  } else if (child_pid == 0) {
+    // pause(); // await cgroup setup
+    raise(SIGSTOP); // await cgroup setup
+    return copy(src_fd, dst_fd);
+  }
+
+  // setup a cgroup for the child
+
+  // wait for the child to pause and restart it
+  int status;
+  if (waitpid(child_pid, &status, WUNTRACED | WSTOPPED) == -1) {
+    perror("waitpid");
+    return -1;
+  }
+
+  if (WIFSTOPPED(status)) {
+    if (kill(child_pid, SIGCONT) == -1) {
+      perror("kill");
+      return -1;
+    }
+  } else {
+    fprintf(stderr, "child behaved unexpectedly\n");
+    return -1;
+  }
+
+  // wait for the child process to terminate
+  if (waitpid(child_pid, &status, 0) == -1) {
+    perror("waitpid");
+    return -1;
+  }
+
+  if (WIFEXITED(status)) {
+    return WEXITSTATUS(status);
+  }
+
+  return -1;
+}