scan: retry reading metadata on error

If label_scan encounters bad vg metadata, invalidate
bcache data for the device and reread the mda_header
and metadata text back to back.  With concurrent commands
modifying large metadata, it's possible that the entire
metadata area can be rewritten in the time between a
command reading the mda_header and reading the metadata
text that the header points to.  Since the label_scan
is just assembling an initial overview of devices, it
doesn't use locking to serialize with other commands
that may be modifying the vg metadata at the same time.

2 files changed, 6 insertions, 0 deletions

diff --git a/lib/label/label.c b/lib/label/label.c
index 50107edc8..ac84b6293 100644
--- a/lib/label/label.c
+++ b/lib/label/label.c
@@ -1704,6 +1704,11 @@ bool dev_invalidate_bytes(struct device *dev, uint64_t start, size_t len)
 	return bcache_invalidate_bytes(scan_bcache, dev->bcache_di, start, len);
 }
 
+void dev_invalidate(struct device *dev)
+{
+	bcache_invalidate_di(scan_bcache, dev->bcache_di);
+}
+
 bool dev_write_zeros(struct device *dev, uint64_t start, size_t len)
 {
 	return dev_set_bytes(dev, start, len, 0);
diff --git a/lib/label/label.h b/lib/label/label.h
index fcdc309ac..32ceebc34 100644
--- a/lib/label/label.h
+++ b/lib/label/label.h
@@ -130,6 +130,7 @@ bool dev_write_bytes(struct device *dev, uint64_t start, size_t len, void *data)
 bool dev_write_zeros(struct device *dev, uint64_t start, size_t len);
 bool dev_set_bytes(struct device *dev, uint64_t start, size_t len, uint8_t val);
 bool dev_invalidate_bytes(struct device *dev, uint64_t start, size_t len);
+void dev_invalidate(struct device *dev);
 void dev_set_last_byte(struct device *dev, uint64_t offset);
 void dev_unset_last_byte(struct device *dev);