Update SAs when an inode is dirtied

Revert the portion of commit d3aa3ea which always resulted in the
SAs being update when an mmap()'ed file was closed.  That change
accidentally resulted in unexpected ctime updates which upset tools
like git.  That was always a horrible hack and I'm happy it will
never make it in to a tagged release.

The right fix is something I initially resisted doing because I
was worried about the additional overhead.  However, in hindsight
the overhead isn't as bad as I feared.

This patch implemented the sops->dirty_inode() callback which is
unsurprisingly called when an inode is dirtied.  We leverage this
callback to keep the znode SAs strictly in sync with the inode.

However, for now we're going to go slowly to avoid introducing
any new unexpected issues by only updating the atime, mtime, and
ctime.  This will cover the callpath of most concern to us.

  ->filemap_page_mkwrite->file_update_time->update_time->
      mark_inode_dirty_sync->__mark_inode_dirty->dirty_inode

Signed-off-by: Brian Behlendorf <[email protected]>
Closes #764
Closes #1140

1 files changed, 20 insertions, 1 deletions

diff --git a/module/zfs/zpl_super.c b/module/zfs/zpl_super.c
index fd4f691e1..d4d4e1b67 100644
--- a/module/zfs/zpl_super.c
+++ b/module/zfs/zpl_super.c
@@ -49,6 +49,25 @@ zpl_inode_destroy(struct inode *ip)
 }
 
 /*
+ * Called from __mark_inode_dirty() to reflect that something in the
+ * inode has changed.  We use it to ensure the znode system attributes
+ * are always strictly update to date with respect to the inode.
+ */
+#ifdef HAVE_DIRTY_INODE_WITH_FLAGS
+static void
+zpl_dirty_inode(struct inode *ip, int flags)
+{
+	zfs_dirty_inode(ip, flags);
+}
+#else
+static void
+zpl_dirty_inode(struct inode *ip)
+{
+	zfs_dirty_inode(ip, 0);
+}
+#endif /* HAVE_DIRTY_INODE_WITH_FLAGS */
+
+/*
  * When ->drop_inode() is called its return value indicates if the
  * inode should be evicted from the inode cache.  If the inode is
  * unhashed and has no links the default policy is to evict it
@@ -306,7 +325,7 @@ zpl_free_cached_objects(struct super_block *sb, int nr_to_scan)
 const struct super_operations zpl_super_operations = {
 	.alloc_inode		= zpl_inode_alloc,
 	.destroy_inode		= zpl_inode_destroy,
-	.dirty_inode		= NULL,
+	.dirty_inode		= zpl_dirty_inode,
 	.write_inode		= NULL,
 	.drop_inode		= NULL,
 #ifdef HAVE_EVICT_INODE