UML now locks the ubd files to avoid booting two UMLs on the same image.v_2_4_19_50

Accordingly, the os interface now has os_lock_file.

3 files changed, 35 insertions, 1 deletions

diff --git a/arch/um/drivers/ubd_user.c b/arch/um/drivers/ubd_user.c
index a756059..39c183f 100644
--- a/arch/um/drivers/ubd_user.c
+++ b/arch/um/drivers/ubd_user.c
@@ -346,6 +346,13 @@ int open_ubd_file(char *file, struct openflags *openflags,
                 if((fd = os_open_file(file, *openflags, mode)) < 0) 
 			return(fd);
         }
+
+	err = os_lock_file(fd, openflags->w);
+	if(err){
+		printk("Failed to lock '%s', errno = %d\n", file, -err);
+		goto error;
+	}
+	
 	if(backing_file_out == NULL) return(fd);
 
 	err = read_cow_header(fd, &magic, &backing_file, &mtime, &size, 
@@ -381,7 +388,7 @@ int open_ubd_file(char *file, struct openflags *openflags,
 
         return(fd);
  error:
-	close(fd);
+	os_close_file(fd);
 	return(err);
 }
 
diff --git a/arch/um/include/os.h b/arch/um/include/os.h
index b495b5b..e3f9dcb 100644
--- a/arch/um/include/os.h
+++ b/arch/um/include/os.h
@@ -107,6 +107,7 @@ extern int create_unix_socket(char *file, int len);
 extern int os_connect_socket(char *name);
 extern int os_file_type(char *file);
 extern int os_file_mode(char *file, struct openflags *mode_out);
+extern int os_lock_file(int fd, int excl);
 
 extern unsigned long os_process_pc(int pid);
 extern int os_process_parent(int pid);
diff --git a/arch/um/os-Linux/file.c b/arch/um/os-Linux/file.c
index 61da438..7919020 100644
--- a/arch/um/os-Linux/file.c
+++ b/arch/um/os-Linux/file.c
@@ -346,6 +346,32 @@ void os_flush_stdout(void)
 	fflush(stdout);
 }
 
+int os_lock_file(int fd, int excl)
+{
+	int type = excl ? F_WRLCK : F_RDLCK;
+	struct flock lock = ((struct flock) { .l_type	= type,
+					      .l_whence	= SEEK_SET,
+					      .l_start	= 0,
+					      .l_len	= 0 } );
+	int err, save;
+
+	err = fcntl(fd, F_SETLK, &lock);
+	if(!err)
+		goto out;
+
+	save = -errno;
+	err = fcntl(fd, F_GETLK, &lock);
+	if(err){
+		err = -errno;
+		goto out;
+	}
+		
+	printk("F_SETLK failed, file already locked by pid %d\n", lock.l_pid);
+	err = save;
+ out:
+	return(err);
+}
+
 /*
  * Overrides for Emacs so that we follow Linus's tabbing style.
  * Emacs will notice this stuff at the end of the file and automatically