[RFC PATCH 3/3] discover: Create dm-snapshots for all eligible devices

[Samuel Mendoza-Jonas]

Create a dm-snapshot for any device with a valid filesystem. This
protects the backing disk from any writes Petitboot may attempt to make
regardless of mount type, such as journal replays.

Signed-off-by: Samuel Mendoza-Jonas <sam.mj at au1.ibm.com>
---
 discover/device-handler.c | 40 +++++++++++++++++++++++++++++-----------
 discover/udev.c           | 20 ++++++++++++++++++--
 2 files changed, 47 insertions(+), 13 deletions(-)

diff --git a/discover/device-handler.c b/discover/device-handler.c
index 69cd699..edf3a0c 100644
--- a/discover/device-handler.c
+++ b/discover/device-handler.c
@@ -1279,11 +1279,14 @@ static const char *fs_parameters(unsigned int rw_flags, const char *fstype)
 static bool check_existing_mount(struct discover_device *dev)
 {
 	struct stat devstat, mntstat;
+	const char *device_path;
 	struct mntent *mnt;
 	FILE *fp;
 	int rc;
 
-	rc = stat(dev->device_path, &devstat);
+	device_path = dev->ramdisk ? dev->ramdisk->snapshot : dev->device_path;
+
+	rc = stat(device_path, &devstat);
 	if (rc) {
 		pb_debug("%s: stat failed: %s\n", __func__, strerror(errno));
 		return false;
@@ -1333,7 +1336,7 @@ static bool check_existing_mount(struct discover_device *dev)
 
 static int mount_device(struct discover_device *dev)
 {
-	const char *fstype;
+	const char *fstype, *device_path;
 	int rc;
 
 	if (!dev->device_path)
@@ -1365,9 +1368,11 @@ static int mount_device(struct discover_device *dev)
 		goto err_free;
 	}
 
+	device_path = dev->ramdisk ? dev->ramdisk->snapshot : dev->device_path;
+
 	pb_log("mounting device %s read-only\n", dev->device_path);
 	errno = 0;
-	rc = mount(dev->device_path, dev->mount_path, fstype,
+	rc = mount(device_path, dev->mount_path, fstype,
 			MS_RDONLY | MS_SILENT,
 			fs_parameters(MS_RDONLY, fstype));
 	if (!rc) {
@@ -1378,7 +1383,10 @@ static int mount_device(struct discover_device *dev)
 	}
 
 	pb_log("couldn't mount device %s: mount failed: %s\n",
-			dev->device_path, strerror(errno));
+			device_path, strerror(errno));
+
+	/* If mount fails clean up any snapshot */
+	discover_device_destroy_snapshot(dev);
 
 	pb_rmdir_recursive(mount_base(), dev->mount_path);
 err_free:
@@ -1389,17 +1397,21 @@ err_free:
 
 static int umount_device(struct discover_device *dev)
 {
+	const char *device_path;
 	int rc;
 
 	if (!dev->mounted || !dev->unmount)
 		return 0;
 
-	pb_log("unmounting device %s\n", dev->device_path);
+	device_path = dev->ramdisk ? dev->ramdisk->snapshot : dev->device_path;
+
+	pb_log("unmounting device %s\n", device_path);
 	rc = umount(dev->mount_path);
 	if (rc)
 		return -1;
 
 	dev->mounted = false;
+	discover_device_destroy_snapshot(dev);
 
 	pb_rmdir_recursive(mount_base(), dev->mount_path);
 
@@ -1411,7 +1423,7 @@ static int umount_device(struct discover_device *dev)
 
 int device_request_write(struct discover_device *dev, bool *release)
 {
-	const char *fstype;
+	const char *fstype, *device_path;
 	int rc;
 
 	*release = false;
@@ -1419,19 +1431,25 @@ int device_request_write(struct discover_device *dev, bool *release)
 	if (!dev->mounted)
 		return -1;
 
+	//FIXME: how do we decide to commit writes, eg from grub save actions?
+	if (!dev->ramdisk)
+		return -1;
+
 	if (dev->mounted_rw)
 		return 0;
 
 	fstype = discover_device_get_param(dev, "ID_FS_TYPE");
 
-	pb_log("remounting device %s read-write\n", dev->device_path);
+	device_path = dev->ramdisk ? dev->ramdisk->snapshot : dev->device_path;
+
+	pb_log("remounting device %s read-write\n", device_path);
 
 	rc = umount(dev->mount_path);
 	if (rc) {
 		pb_log("Failed to unmount %s\n", dev->mount_path);
 		return -1;
 	}
-	rc = mount(dev->device_path, dev->mount_path, fstype,
+	rc = mount(device_path, dev->mount_path, fstype,
 			MS_SILENT,
 			fs_parameters(MS_REMOUNT, fstype));
 	if (rc)
@@ -1442,12 +1460,12 @@ int device_request_write(struct discover_device *dev, bool *release)
 	return 0;
 
 mount_ro:
-	pb_log("Unable to remount device %s read-write\n", dev->device_path);
-	rc = mount(dev->device_path, dev->mount_path, fstype,
+	pb_log("Unable to remount device %s read-write\n", device_path);
+	rc = mount(device_path, dev->mount_path, fstype,
 			MS_RDONLY | MS_SILENT,
 			fs_parameters(MS_RDONLY, fstype));
 	if (rc)
-		pb_log("Unable to recover mount for %s\n", dev->device_path);
+		pb_log("Unable to recover mount for %s\n", device_path);
 	return -1;
 }
 
diff --git a/discover/udev.c b/discover/udev.c
index 6ccb8d4..8a3cabb 100644
--- a/discover/udev.c
+++ b/discover/udev.c
@@ -94,12 +94,16 @@ static int udev_handle_block_add(struct pb_udev *udev, struct udev_device *dev,
 
 	node = udev_device_get_devnode(dev);
 	path = udev_device_get_devpath(dev);
-	if (path && (strstr(path, "virtual/block/loop")
-			|| strstr(path, "virtual/block/ram"))) {
+	if (path && strstr(path, "virtual/block/loop")) {
 		pb_log("SKIP: %s: ignored (path=%s)\n", name, path);
 		return 0;
 	}
 
+	if (path && strstr(path, "virtual/block/ram")) {
+		device_handler_add_ramdisk(udev->handler, node);
+		return 0;
+	}
+
 	cdrom = node && !!udev_device_get_property_value(dev, "ID_CDROM");
 	if (cdrom) {
 		/* CDROMs require a little initialisation, to get
@@ -111,6 +115,14 @@ static int udev_handle_block_add(struct pb_udev *udev, struct udev_device *dev,
 		}
 	}
 
+	/* dm-snapshots don't appear as udev events currently, but catch this
+	 * in case udev/libdm are updated in Petitboot's environment */
+	const char *devname = udev_device_get_property_value(dev, "DM_NAME");
+	if (devname) {
+		pb_log("This is a snapshot! %s\n", devname);
+		return 0;
+	}
+
 	type = udev_device_get_property_value(dev, "ID_FS_TYPE");
 	if (!type) {
 		pb_log("SKIP: %s: no ID_FS_TYPE property\n", name);
@@ -142,6 +154,10 @@ static int udev_handle_block_add(struct pb_udev *udev, struct udev_device *dev,
 
 	udev_setup_device_params(dev, ddev);
 
+	/* Create snapshot first if needed */
+	if (ddev->device->type == DEVICE_TYPE_DISK)
+		device_handler_create_snapshot(udev->handler, ddev);
+
 	device_handler_discover(udev->handler, ddev);
 
 	return 0;
-- 
2.1.0