Add solution for exercise 2.9.1 (free memory)

Author: dwrz

Makefile

@@ -132,6 +132,7 @@ UPROGS=\
 	$U/_grind\
 	$U/_wc\
 	$U/_zombie\
+	$U/_mfree\
 
 fs.img: mkfs/mkfs README $(UPROGS)
 	mkfs/mkfs fs.img README $(UPROGS)

kernel/kalloc.c

@@ -80,3 +80,20 @@ kalloc(void)
     memset((char*)r, 5, PGSIZE); // fill with junk
   return (void*)r;
 }
+
+uint64
+sys_mfree(void)
+{
+  int free = 0;
+  struct run *r;
+
+  // Iterate through the freelist and count free pages.
+  acquire(&kmem.lock);
+  for(r = kmem.freelist; r != 0; r = r->next) {
+    free++;
+  }
+  release(&kmem.lock);
+
+  // Return the number of bytes of all free pages.
+  return free * PGSIZE;
+}

kernel/syscall.c

@@ -104,6 +104,7 @@ extern uint64 sys_unlink(void);
 extern uint64 sys_wait(void);
 extern uint64 sys_write(void);
 extern uint64 sys_uptime(void);
+extern uint64 sys_mfree(void);
 
 static uint64 (*syscalls[])(void) = {
 [SYS_fork]    sys_fork,
@@ -127,6 +128,7 @@ static uint64 (*syscalls[])(void) = {
 [SYS_link]    sys_link,
 [SYS_mkdir]   sys_mkdir,
 [SYS_close]   sys_close,
+[SYS_mfree]   sys_mfree,
 };
 
 void

kernel/syscall.h

@@ -20,3 +20,4 @@
 #define SYS_link   19
 #define SYS_mkdir  20
 #define SYS_close  21
+#define SYS_mfree  22

user/mfree.c

@@ -0,0 +1,11 @@
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "user/user.h"
+
+int
+main(int argc, char *argv[])
+{
+  printf("%d\n", mfree());
+
+  exit(0);
+}

user/user.h

@@ -23,6 +23,7 @@ int getpid(void);
 char* sbrk(int);
 int sleep(int);
 int uptime(void);
+int mfree(void);
 
 // ulib.c
 int stat(const char*, struct stat*);

user/usys.pl

@@ -36,3 +36,4 @@ sub entry {
 entry("sbrk");
 entry("sleep");
 entry("uptime");
+entry("mfree");