From b851113ef17c6f0106c53d271ec52892c942a7a0 Mon Sep 17 00:00:00 2001
From: Qu Wenruo <wqu@suse.com>
Date: Thu, 29 Apr 2021 17:06:57 +0800
Subject: [PATCH] btrfs-progs: image: enlarge output file if no tree
 modification is needed for restore

[BUG]
If restoring dumped image to a new file, under most cases kernel will
reject it since version 5.11:

 # mkfs.btrfs -f /dev/test/test
 # btrfs-image /dev/test/test /tmp/dump
 # btrfs-image -r /tmp/dump ~/test.img
 # mount ~/test.img /mnt/btrfs
 mount: /mnt/btrfs: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error.
 # dmesg -t | tail -n 7
 loop0: detected capacity change from 10592 to 0
 BTRFS info (device loop0): disk space caching is enabled
 BTRFS info (device loop0): has skinny extents
 BTRFS info (device loop0): flagging fs with big metadata feature
 BTRFS error (device loop0): device total_bytes should be at most 5423104 but found 10737418240
 BTRFS error (device loop0): failed to read chunk tree: -22
 BTRFS error (device loop0): open_ctree failed

[CAUSE]
When btrfs-image restores an image into a file, and the source image
contains only single device, then we don't need to modify the
chunk/device tree, as we can reuse the existing chunk/dev tree without
any problem.

This also means, for such restore, we also won't do any target file
enlarge. This behavior itself is fine, as at that time, kernel won't
check if the device is smaller than the device size recorded in device
tree.

But later kernel commit 3a160a933111 ("btrfs: drop never met disk total
bytes check in verify_one_dev_extent") introduces new check on device
size at mount time, rejecting any loop file which is smaller than the
original device size.

[FIX]
Do extra file enlarge for single device restore if the restored file is
smaller than the device size.

Reported-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Su Yue <l@damenly.su>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 image/main.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/image/main.c b/image/main.c
index 44e85c3f..b29e68f8 100644
--- a/image/main.c
+++ b/image/main.c
@@ -2708,6 +2708,51 @@ static int restore_metadump(const char *input, FILE *out, int old_restore,
 		close_ctree(info->chunk_root);
 		if (ret)
 			goto out;
+	} else {
+		struct btrfs_root *root;
+		struct stat st;
+		u64 dev_size;
+
+		if (!info) {
+			root = open_ctree_fd(fileno(out), target, 0, 0);
+			if (!root) {
+				error("open ctree failed in %s", target);
+				ret = -EIO;
+				goto out;
+			}
+
+			info = root->fs_info;
+
+			dev_size = btrfs_stack_device_total_bytes(
+					&info->super_copy->dev_item);
+			close_ctree(root);
+			info = NULL;
+		} else {
+			dev_size = btrfs_stack_device_total_bytes(
+					&info->super_copy->dev_item);
+		}
+
+		/*
+		 * We don't need extra tree modification, but if the output is
+		 * a file, we need to enlarge the output file so that 5.11+
+		 * kernel won't report an error.
+		 */
+		ret = fstat(fileno(out), &st);
+		if (ret < 0) {
+			error("failed to stat result image: %m");
+			ret = -errno;
+			goto out;
+		}
+		if (S_ISREG(st.st_mode) && st.st_size < dev_size) {
+			ret = ftruncate64(fileno(out), dev_size);
+			if (ret < 0) {
+				error(
+		"failed to enlarge result image file from %llu to %llu: %m",
+					(unsigned long long)st.st_size, dev_size);
+				ret = -errno;
+				goto out;
+			}
+		}
 	}
 out:
 	mdrestore_destroy(&mdrestore, num_threads);