[PATCH v4 07/24] make sure partially read index is not changed

[Thomas Gummerer <t.gummerer@gmail.com>]

A partially read index file currently cannot be written to disk.  Make
sure that never happens by erroring out when a caller tries to write a
partially read index.  Do the same when trying to re-read a partially
read index without having discarded it first to avoid losing any
information.

Forcing the caller to load the right part of the index file, instead of
re-reading it when changing it, gives a bit of a performance advantage
by avoiding reading parts of the index twice.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
---
 read-cache.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/read-cache.c b/read-cache.c
index 01f5397..7020f26 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1330,6 +1330,8 @@ int read_index_filtered_from(struct index_state *istate, const char *path,
 	void *mmap;
 	size_t mmap_size;
 
+	if (istate->filter_opts)
+		die("BUG: cannot re-read partially read index");
 	errno = EBUSY;
 	if (istate->initialized)
 		return istate->cache_nr;
@@ -1452,6 +1454,8 @@ void update_index_if_able(struct index_state *istate, struct lock_file *lockfile
 
 int write_index(struct index_state *istate, int newfd)
 {
+	if (istate->filter_opts)
+		die("BUG: cannot write a partially read index");
 	return istate->ops->write_index(istate, newfd);
 }
 
-- 
1.8.4.2