Fix: start_block misalignment caused by SIGSTOP (#552)

Author: amissael95

messages/libltfs/root.txt

@@ -834,6 +834,8 @@ v
 		17290I:string { "Partitioning the medium with the destructive method." }
 		17291I:string { "Unpartitioning the medium with the destructive method." }
 		17292I:string { "Current position is (%llu, %llu), Error position is (%llu, %llu)." }
+	 	17293E:string { "Position mismatch. Cached tape position = %llu. Current tape position = %llu." }
+	 	17294I:string { "Continue signal (%d) received" }
 
 		// For Debug 19999I:string { "%s %s %d." }
 

src/libltfs/ltfs.c

@@ -205,6 +205,58 @@ bool ltfs_is_interrupted(void)
 	return interrupted;
 }
 
+bool caught_sigcont = false;
+void _ltfs_sigcont(int signal)
+{
+	ltfsmsg(LTFS_INFO, 17294I, signal);
+	ltfs_sigcont_set(true);
+}
+
+void ltfs_sigcont_set(bool sig_val)
+{
+	caught_sigcont = sig_val;
+}
+
+bool ltfs_caught_sigcont(void)
+{
+	return caught_sigcont;
+}
+
+int ltfs_extra_signal_handlers(void)
+#ifdef mingw_PLATFORM
+{
+	return 0;
+}
+#else
+{
+	ltfs_sighandler_t ret;
+	ret = signal(SIGCONT, _ltfs_sigcont);
+	if (ret == SIG_ERR) {
+		return -LTFS_SIG_HANDLER_ERR;
+	}
+
+	return 0;
+}
+#endif
+
+int ltfs_unset_extra_signal_handler(void)
+#ifdef mingw_PLATFORM
+{
+	return 0;
+}
+#else
+{
+	ltfs_sighandler_t rc;
+	int ret = 0;
+
+	rc = signal(SIGCONT, SIG_DFL);
+	if (rc == SIG_ERR)
+		ret = -LTFS_SIG_HANDLER_ERR;
+
+	return ret;
+}
+#endif
+
 /**
  * This function can be used to enable libltfs signal handler
  * to kill ltfs, mkltfs, ltfsck cleanly
@@ -2383,12 +2435,13 @@ int ltfs_write_index(char partition, char *reason, struct ltfs_volume *vol)
 	struct tape_offset old_selfptr, old_backptr;
 	struct ltfs_timespec modtime_old = { .tv_sec = 0, .tv_nsec = 0 };
 	bool generation_inc = false;
-	struct tc_position physical_selfptr;
+	struct tc_position physical_selfptr, current_position;
 	char *cache_path_save = NULL;
 	bool write_perm = (strcmp(reason, SYNC_WRITE_PERM) == 0);
 	bool update_vollock = false;
 	int volstat = -1, new_volstat = 0;
 	char *bc_print = NULL;
+	unsigned long long diff;
 
 	CHECK_ARG_NULL(vol, -LTFS_NULL_ARG);
 
@@ -2505,6 +2558,24 @@ int ltfs_write_index(char partition, char *reason, struct ltfs_volume *vol)
 		vol->index->backptr = old_backptr;
 		goto out_write_perm;
 	}
+
+	/* Get the tape position from the tape drive by using the SCSI command READPOS*/
+	ret = tape_get_position_from_drive(vol->device, &current_position);
+	if (ret < 0) {
+		/* Return error since the current tape position was unable to be determined, so there could be an undetected position mismatch */
+		ltfsmsg(LTFS_ERR, 11081E, ret);
+		return -1;
+	}
+
+	/* Prior to writing the index, compare the current location of the head position to the head location 
+	that is kept in the cache of ltfs (physical_selfptr). If they are different return error (-1) */
+	diff = ((unsigned long long)physical_selfptr.block - (unsigned long long)current_position.block);
+	if (diff) {
+		/* Position mismatch, diff not equal zero */
+		ltfsmsg(LTFS_INFO, 17293E, (unsigned long long)physical_selfptr.block, (unsigned long long)current_position.block);
+		return -1;
+	}
+
 	old_selfptr = vol->index->selfptr;
 	vol->index->selfptr.partition = partition;
 	vol->index->selfptr.partition = vol->label->part_num2id[physical_selfptr.partition];

src/libltfs/ltfs.h

@@ -592,8 +592,12 @@ int ltfs_fs_init(void);
 void ltfs_set_log_level(int log_level);
 void ltfs_set_syslog_level(int syslog_level);
 bool ltfs_is_interrupted(void);
+bool ltfs_caught_sigcont(void);
+void ltfs_sigcont_set(bool sig_val);
 int ltfs_set_signal_handlers(void);
 int ltfs_unset_signal_handlers(void);
+int ltfs_extra_signal_handlers(void);
+int ltfs_unset_extra_signal_handler(void);
 int ltfs_finish();
 
 /* Public wrappers for tape_* functions */

src/libltfs/tape.c

@@ -1105,7 +1105,7 @@ int tape_get_position(struct device_data *dev, struct tc_position *pos)
 /**
  * Get current tape position by querying the device.
  */
-int tape_update_position(struct device_data *dev, struct tc_position *pos)
+int tape_get_position_from_drive(struct device_data *dev, struct tc_position *pos)
 {
 	int ret;
 
@@ -1187,6 +1187,9 @@ int tape_spacefm(struct device_data *dev, int count)
 ssize_t tape_write(struct device_data *dev, const char *buf, size_t count, bool ignore_less, bool ignore_nospc)
 {
 	ssize_t ret;
+	struct tc_position current_position;
+	int ret_for_current_position = 0;
+	unsigned long long diff = 0;
 
 	CHECK_ARG_NULL(dev, -LTFS_NULL_ARG);
 	CHECK_ARG_NULL(buf, -LTFS_NULL_ARG);
@@ -1241,6 +1244,25 @@ ssize_t tape_write(struct device_data *dev, const char *buf, size_t count, bool
 			count = -LTFS_LESS_SPACE;
 	}
 
+	if (ltfs_caught_sigcont()) {
+		// Unset flag to avoid checking it again if it is not needed 
+		ltfs_sigcont_set(false);
+
+		ret_for_current_position = tape_get_position_from_drive(dev, &current_position);
+		if (ret_for_current_position) {
+			/* Return error since the current tape position was unable to be determined, so there could be an undetected position mismatch */
+			ltfsmsg(LTFS_ERR, 11081E, ret);
+			return -LTFS_WRITE_ERROR;
+		}
+
+		diff = ((unsigned long long)dev->position.block - (unsigned long long)current_position.block);
+		if (diff) {
+			/* Position mismatch, diff not equal zero */
+			ltfsmsg(LTFS_INFO, 17293E, (unsigned long long)dev->position.block, (unsigned long long)current_position.block);
+			return -LTFS_WRITE_ERROR;
+		}
+	}
+
 	ltfs_mutex_lock(&dev->append_pos_mutex);
 	dev->append_pos[dev->position.partition] = dev->position.block;
 	ltfs_mutex_unlock(&dev->append_pos_mutex);

src/libltfs/tape.h

@@ -160,7 +160,7 @@ int tape_force_read_only(struct device_data *dev);
 
 int tape_rewind(struct device_data *dev);
 int tape_get_position(struct device_data *dev, struct tc_position *pos);
-int tape_update_position(struct device_data *dev, struct tc_position *pos);
+int tape_get_position_from_drive(struct device_data *dev, struct tc_position *pos);
 
 int tape_seek(struct device_data *dev, struct tc_position *pos);
 int tape_seek_eod(struct device_data *dev, tape_partition_t partition);

src/main.c

@@ -1241,10 +1241,14 @@ int single_drive_main(struct fuse_args *args, struct ltfs_fuse_data *priv)
 	ltfsmsg(LTFS_INFO, 14111I);
 	ltfsmsg(LTFS_INFO, 14112I);
 	ltfsmsg(LTFS_INFO, 14113I);
+	/* Set handlers for signals that need to be caught while fuse main is running*/
+	ltfs_extra_signal_handlers();
 	ret = fuse_main(args->argc, args->argv, &ltfs_ops, priv);
 	if (ret != 0) {
 		ltfsmsg(LTFS_WARN, 14123W, ret);
 	}
+	/* Unset extra handlers once fuse main exits */
+	ltfs_unset_extra_signal_handler();
 
 	/*  Setup signal handler again to terminate cleanly */
 	ret = ltfs_set_signal_handlers();