Flock system call

Xv6-OS-with-custom-modifications/.gitignore

@@ -1,3 +1,4 @@
+.vscode
 *~
 _*
 *.o

Xv6-OS-with-custom-modifications/defs.h

@@ -196,6 +196,16 @@ void clearpteu(pde_t *pgdir, char *uva);
 // kshutdown.c
 void            shutdown(void);
 
+/// @brief This fuction acquires a sleep lock for the given file.
+/// @param fp a valid file pointer
+/// @return 0 upon success and -1 upon error
+int             filelock(struct file* fp);
+
+/// @brief This fuction releases a sleep lock for the given file.
+/// @param fp a valid file pointer
+/// @return 0 upon success and -1 upon error
+int             fileunlock(struct file* fp);
+
 // number of elements in fixed-size array
 #define NELEM(x) (sizeof(x) / sizeof((x)[0]))
 

Xv6-OS-with-custom-modifications/file.h

@@ -18,6 +18,7 @@ struct inode {
   uint32_t dev;          // Device number
   uint32_t inum;         // Inode number
   int ref;               // Reference count
+  struct sleeplock flock; // protects everything below hereNDIRECT
   struct sleeplock lock; // protects everything below hereNDIRECT
   int valid;             // inode has been read from disk?
 

Xv6-OS-with-custom-modifications/kkernel/dhello.c

@@ -26,7 +26,7 @@ static int s_cnputs(char *outbuffer, int n, const char* string)
 int
 helloread(struct inode *ip, char *dst, int n)
 {
-    return s_cnputs(dst, n, "Hello, World!");
+    return s_cnputs(dst, n, "Hello, World!\n");
 }
 
 int

Xv6-OS-with-custom-modifications/kkernel/kfile.c

@@ -2,8 +2,8 @@
 // File descriptors
 //
 
-#include "file.h"
 #include "defs.h"
+#include "file.h"
 #include "fs.h"
 #include "param.h"
 #include "sleeplock.h"
@@ -16,6 +16,28 @@ struct {
   struct file file[NFILE];
 } ftable;
 
+int filelock(struct file *fp) {
+  int status = 0;
+  if (fp->ip == 0 || fp->ip->ref < 1) {
+    status = -1;
+  } else {
+    acquiresleep(&fp->ip->flock);
+  }
+
+  return status;
+}
+
+int fileunlock(struct file *fp) {
+  int status = -1;
+
+  if (fp->ip != 0 && holdingsleep(&fp->ip->flock) && !(fp->ip->ref < 1)) {
+    releasesleep(&fp->ip->flock);
+    status = 0;
+  }
+
+  return status;
+}
+
 void fileinit(void) { initlock(&ftable.lock, "ftable"); }
 
 // Allocate a file structure.

Xv6-OS-with-custom-modifications/kkernel/syscall.c

@@ -102,6 +102,8 @@ extern int sys_write(void);
 extern int sys_uptime(void);
 
 extern int sys_shutdown(void);
+extern int sys_flock(void);
+extern int sys_funlock(void);
 
 static int (*syscalls[])(void) = {
     [SYS_fork] = sys_fork,     [SYS_exit] = sys_exit,
@@ -115,6 +117,7 @@ static int (*syscalls[])(void) = {
     [SYS_mknod] = sys_mknod,   [SYS_unlink] = sys_unlink,
     [SYS_link] = sys_link,     [SYS_mkdir] = sys_mkdir,
     [SYS_close] = sys_close,   [SYS_shutdown] = sys_shutdown,
+    [SYS_flock] = sys_flock,   [SYS_funlock] = sys_funlock,
 };
 
 void syscall(void) {

Xv6-OS-with-custom-modifications/kkernel/sysfile.c

@@ -445,3 +445,24 @@ int sys_pipe(void) {
   fd[1] = fd1;
   return 0;
 }
+
+
+int 
+sys_flock(void) {
+  struct file *fp;
+  if(argfd(0, 0, &fp) >= 0) {
+    return filelock(fp);
+  }
+  cprintf("***** %s\n", "sys_flock FAILED");
+  return -1;
+}
+
+int 
+sys_funlock(void) {
+  struct file *fp;
+  if(argfd(0, 0, &fp) >= 0) {
+    return fileunlock(fp);
+  }
+  cprintf("***** %s\n", "sys_funlock FAILED");
+  return -1;
+}

Xv6-OS-with-custom-modifications/param.h

@@ -12,6 +12,6 @@
 #define MAXOPBLOCKS 10            // max # of blocks any FS op writes
 #define LOGSIZE (MAXOPBLOCKS * 3) // max data blocks in on-disk log
 #define NBUF (MAXOPBLOCKS * 3)    // size of disk block cache
-#define FSSIZE 1000               // size of file system in blocks
+#define FSSIZE 2000               // size of file system in blocks
 
 #endif /* A4559DE9_C220_44C9_96A3_C431CF69CB63 */

Xv6-OS-with-custom-modifications/syscall.h

@@ -26,5 +26,7 @@
 #define SYS_close 21
 
 #define SYS_shutdown  22
+#define SYS_flock  23
+#define SYS_funlock  24
 
 #endif /* D403047C_65A6_4017_9DFB_514095C998F7 */

Xv6-OS-with-custom-modifications/user.h

@@ -28,6 +28,21 @@ int uptime(void);
 
 int shutdown(void);
 
+/// @brief call this function pasing the file descriptor for an open file in 
+/// order to acquire a sleep lock associated with the open file. This function
+/// blocks (a.k.a. sleeps) until the lock is acquired.
+/// @param[in] fd descriptor for a file opened with open()
+/// @return zero if lock is acquired and a negative number if any error is detected.
+int flock(int fd);
+
+/// @brief call this function pasing the file descriptor for an open file 
+/// that is currently locked via flock(). This function unlocks the lock 
+/// associated with the file. 
+/// @param fd descriptor for a file opened with open() and locked with flock()
+/// @return zero if lock is released and a negative number if any error is 
+/// detected.
+int funlock(int fd);
+
 // ulib.c
 int stat(const char *, struct stat *);
 char *strcpy(char *, const char *);

Xv6-OS-with-custom-modifications/user/Makefile

@@ -56,6 +56,7 @@ ULIB = ../ulib.o ../usys.o ../printf.o ../malloc.o
 .PRECIOUS: %.o
 
 UPROGS=\
+	_countUD\
 	_cat\
 	_cp\
 	_echo\
@@ -74,7 +75,8 @@ UPROGS=\
 	_testfs\
 	_testuser\
 	_testdevhello\
-	_ex\
+	_stuff\
+	_testflock\
 
 all: $(UPROGS)
 

Xv6-OS-with-custom-modifications/user/stuff.c

@@ -0,0 +1,18 @@
+#include "stat.h"
+#include "types.h"
+#include "user.h"
+#include "fcntl.h" // For O_ constants
+
+int main(int argc, const char *argv[]) {
+  int consoleLock = open("consoleLock", O_CREATE|O_RDWR);
+
+  const char* message = "Stuff\n";
+  for (int i = 0; i < 1000; ++i) {
+    flock(consoleLock);
+    for(int j = 0; j < 7; ++j) {
+      write(1, &message[j], 1);
+    }
+    funlock(consoleLock);
+  }
+  close(consoleLock);
+}

Xv6-OS-with-custom-modifications/user/testflock.c

@@ -0,0 +1,15 @@
+#include "types.h"
+#include "stat.h"
+#include "user.h"
+#include "fcntl.h" // For O_CREATE
+
+int
+main(int argc, char *argv[])
+{
+    int lockFd = open("consoleLock", O_CREATE|O_RDWR);
+    printf(1, "lockFd is %d\n", lockFd);
+    flock(lockFd);
+    flock(lockFd);
+    funlock(lockFd);
+    exit();
+}

Xv6-OS-with-custom-modifications/usys.S

@@ -31,3 +31,5 @@ SYSCALL(sleep)
 SYSCALL(uptime)
 
 SYSCALL(shutdown)
+SYSCALL(flock)
+SYSCALL(funlock)