From a140f0bc0f481a65d5517cb0d852e21a22da0e5b Mon Sep 17 00:00:00 2001
From: Remzi Arpaci <remzi@Remzi-SmallMac.local>
Date: Thu, 12 Aug 2021 22:07:53 -0500
Subject: [PATCH] updated version

---
 file-intro/pstack_assert.c | 74 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 file-intro/pstack_assert.c

diff --git a/file-intro/pstack_assert.c b/file-intro/pstack_assert.c
new file mode 100644
index 0000000..8aafb08
--- /dev/null
+++ b/file-intro/pstack_assert.c
@@ -0,0 +1,74 @@
+// Persistent stack example of how mmap() naturally creates a software abstraction of persistent memory.
+// Author: Terence Kelly
+//         tpkelly @ { acm.org, cs.princeton.edu, eecs.umich.edu }
+
+// Note:  Use 'truncate' to make the initial (empty) backing file,
+// whose size should be a multiple of the system page size:
+//
+//     prompt> getconf PAGESIZE
+//     4096
+//     prompt> truncate -s 4096 ps.img
+//
+// makes a 4096-byte empty file.  The first sizeof(size_t) bytes will
+// be interprted as the number of items on the stack; the remainder
+// of the file will contain the integers contained in the stack.
+// Now you can run the program:
+//
+//     prompt> ./pstack 7 13 47 pop
+//     47
+//     prompt> ./pstack pop pop 99
+//     13
+//     7
+//     prompt> ./pstack pop
+//     99
+//
+// Notice that items push'd in one invocation of the program persist
+// until the next invocation:  The stack is persistent.
+//
+// You can use hexdump to examine the contents of the backing file:
+//
+//     prompt> hexdump ps.img
+
+#include <assert.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+typedef struct {
+    size_t n;
+    int stack[]; // zero-length per C99
+} pstack_t;
+
+int main(int argc, char *argv[]) {
+    int fd, rc;
+    struct stat s;
+    size_t file_size;
+    pstack_t *p;
+
+    fd = open("ps.img", O_RDWR);
+    assert(fd > -1);
+    rc = fstat(fd, &s);
+    assert(rc == 0);
+
+    file_size = (size_t) s.st_size;
+    assert(file_size >= sizeof(pstack_t) && file_size % sizeof(int) == 0);
+
+    p = (pstack_t *) mmap(NULL, file_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+    assert(p != MAP_FAILED);
+
+    for (int i = 1; i < argc; i++)
+        if (strcmp(argv[i], "pop") == 0) {
+            if (p->n > 0)  // stack not empty
+                printf("%d\n", p->stack[--p->n]);
+        } else {  // pop
+          if (sizeof(pstack_t) + (1 + p->n) * sizeof(int) <= file_size)  // stack not full
+                p->stack[p->n++] = atoi(argv[i]);
+        }
+    (void) close(fd);
+    return 0;
+}