btrfs-progs: add new flag to read superblock with mismatched fsids

New flag that mimics OPEN_CTREE_IGNORE_FSID_MISMATCH but only for
reading the superblock. It should be passed around to various helpers
like scan or mount checks as they'd fail before we'd get to the final
caller that can do something useful with the filesystem.

This will be used for an interrupted 'btrfstune -u'.

Note to __open_ctree_fd: the RECOVERY mode is not compatible with that
flag

Signed-off-by: David Sterba <dsterba@suse.com>

2 files changed, 9 insertions, 0 deletions

diff --git a/disk-io.c b/disk-io.c
index 4a609a89..1caa7cd0 100644
--- a/disk-io.c
+++ b/disk-io.c
@@ -1125,6 +1125,9 @@ static struct btrfs_fs_info *__open_ctree_fd(int fp, const char *path,
 	if (flags & OPEN_CTREE_TEMPORARY_SUPER)
 		sbflags = SBREAD_TEMPORARY;
 
+	if (flags & OPEN_CTREE_IGNORE_FSID_MISMATCH)
+		sbflags |= SBREAD_IGNORE_FSID_MISMATCH;
+
 	ret = btrfs_scan_fs_devices(fp, path, &fs_devices, sb_bytenr, sbflags,
 			(flags & OPEN_CTREE_NO_DEVICES));
 	if (ret)
diff --git a/disk-io.h b/disk-io.h
index fefdb0a7..b4a1b104 100644
--- a/disk-io.h
+++ b/disk-io.h
@@ -100,6 +100,12 @@ enum btrfs_read_sb_flags {
 	 * SBREAD_RECOVER
 	 */
 	SBREAD_TEMPORARY = (1 << 1),
+
+	/*
+	 * Equivalent of OPEN_CTREE_IGNORE_FSID_MISMATCH, allow to read
+	 * superblock that has mismatched sb::fsid and sb::dev_item.fsid
+	 */
+	SBREAD_IGNORE_FSID_MISMATCH = (1 << 2),
 };
 
 /*