udf: Don't write integrity descriptor too often

We update information in logical volume integrity descriptor after each
allocation (as LVID contains free space, number of directories and files on
disk etc.). If the filesystem is on some phase change media, this leads to its
quick degradation as such media is able to handle only 10000 overwrites or so.
We solve the problem by writing new information into LVID only on umount,
remount-ro and sync. This solves the problem at the price of longer media
inconsistency (previously media became consistent after pdflush flushed dirty
LVID buffer) but that should be acceptable.

Report by and patch written in cooperation with
Rich Coe <Richard.Coe@med.ge.com>.

Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/udf/udf_sb.h b/fs/udf/udf_sb.h
index 46fea3ea70a9..d113b72c2768 100644
--- a/fs/udf/udf_sb.h
+++ b/fs/udf/udf_sb.h
@@ -148,6 +148,8 @@ struct udf_sb_info {
         struct inode            *s_vat_inode;
 
         struct mutex            s_alloc_mutex;
+        /* Protected by s_alloc_mutex */
+        unsigned int            s_lvid_dirty;
 };
 
 static inline struct udf_sb_info *UDF_SB(struct super_block *sb)