libmount: add reference counting to libmount_fs

 * mnt_new_fs() returns object with refcount=1
 * mnt_free_fs() does not care about reference counter

 * new functions mnt_ref_fs() and mnt_unref_fs()

 * mnt_table_add_fs() and mnt_table_rem_fs() uses reference counter

 * libmmnt_context uses reference counter for internal FS (as it could be
   shared outside the context)

 * backwardly incompatible change:

	- FS could be deallocated after mnt_table_remove_fs()

 * it's recommended to use mnt_unref_fs() after mnt_table_add_fs()

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/libmount/src/tab_diff.c b/libmount/src/tab_diff.c
index 0ebdc1110..71ef0f419 100644
--- a/libmount/src/tab_diff.c
+++ b/libmount/src/tab_diff.c
@@ -54,6 +54,8 @@ static void free_tabdiff_entry(struct tabdiff_entry *de)
 	if (!de)
 		return;
 	list_del(&de->changes);
+	mnt_unref_fs(de->new_fs);
+	mnt_unref_fs(de->old_fs);
 	free(de);
 }
 
@@ -135,6 +137,9 @@ static int tabdiff_reset(struct libmnt_tabdiff *df)
 		list_del(&de->changes);
 		list_add_tail(&de->changes, &df->unused);
 
+		mnt_unref_fs(de->new_fs);
+		mnt_unref_fs(de->old_fs);
+
 		de->new_fs = de->old_fs = NULL;
 		de->oper = 0;
 	}
@@ -164,6 +169,12 @@ static int tabdiff_add_entry(struct libmnt_tabdiff *df, struct libmnt_fs *old,
 
 	INIT_LIST_HEAD(&de->changes);
 
+	mnt_ref_fs(new);
+	mnt_ref_fs(old);
+
+	mnt_unref_fs(de->new_fs);
+	mnt_unref_fs(de->old_fs);
+
 	de->old_fs = old;
 	de->new_fs = new;
 	de->oper = oper;
@@ -280,6 +291,8 @@ int mnt_diff_tables(struct libmnt_tabdiff *df, struct libmnt_table *old_tab,
 
 			de = tabdiff_get_mount(df, src,	mnt_fs_get_id(fs));
 			if (de) {
+				mnt_ref_fs(fs);
+				mnt_unref_fs(de->old_fs);
 				de->oper = MNT_TABDIFF_MOVE;
 				de->old_fs = fs;
 			} else