zipl/src: Introduce misc_open_simulate() and misc_open_device()

Introduce misc_open_simulate() to mark individual files as "opened
for write simulation".
Introduce misc_open_device() to open a file either in "usual", or
in "simulation" mode, depending on the passed argument

Tested-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Reviewed-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Signed-off-by: Eduard Shishkin <edward6@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zipl/include/misc.h

@@ -34,6 +34,8 @@ int misc_asprintf(char **out, const char *fmt, ...);
 void* misc_calloc(size_t n, size_t size);
 char* misc_strdup(const char* s);
 int misc_open_exclusive(const char* filename);
+int misc_open_simulate(const char *filename, struct misc_fd *mfd);
+int misc_open_device(const char *filename, struct misc_fd *mfd, int simulate);
 int misc_read(int fd, void* buffer, size_t count);
 int misc_read_file(const char* filename, char** buffer, size_t* size,
 		   int nil_terminate);

zipl/src/misc.c

@@ -101,6 +101,35 @@ misc_open_exclusive(const char* filename)
 	return fd;
 }
 
+/**
+ * Open file FILENAME for write simulation
+ */
+int misc_open_simulate(const char *filename, struct misc_fd *mfd)
+{
+	/*
+	 * In write simulation mode actual data are not written to the file,
+	 * so open it as read-only
+	 */
+	mfd->fd = open(filename, O_RDONLY);
+	mfd->simulate_write = 1;
+	if (mfd->fd == -1)
+		error_reason(strerror(errno));
+	return mfd->fd;
+}
+
+int misc_open_device(const char *filename, struct misc_fd *mfd, int simulate)
+{
+	if (simulate) {
+		/*
+		 * open the file for "write simulation", when actual
+		 * data are not written, and only current position in
+		 * the file is updated
+		 */
+		return misc_open_simulate(filename, mfd);
+	}
+	mfd->fd = misc_open_exclusive(filename);
+	return mfd->fd;
+}
 
 /* Read COUNT bytes of data from file identified by file descriptor FD to
  * memory at location BUFFER. Return 0 when all bytes were successfully read,