[RFC PATCH] midx.c: clean up .rev file

[haoyurenzhuxia@xxxxxxxxx]

From: Xia XiaoWen <haoyurenzhuxia@xxxxxxxxx>

The command: `git multi-pack-index write --bitmap` will create 3
files in `objects/pack/`:
    * multi-pack-index
    * multi-pack-index-*.bitmap
    * multi-pack-index-*.rev

But if the command is terminated by the user (such as Ctl-C) or
the system, the midx reverse index file (`multi-pack-index-*.rev`)
is not removed and still exists in `objects/pack/`:

    $ GIT_TEST_MIDX_WRITE_REV=1 git multi-pack-index write --bitmap
    Selecting bitmap commits: 133020, done.
    Building bitmaps:   0% (3/331)
    ^C^C

    $ tree objects/pack/
    objects/pack/
    ├── multi-pack-index-3b048d1b965842cd866e10b6ec1a3035dbede0a5.rev
    ├── pack-b7d425f1b01727d5f364f5d9fbab2d1900fcd5c0.idx
    └── pack-b7d425f1b01727d5f364f5d9fbab2d1900fcd5c0.pack

This patch resolves this by adding a cleanup handler to the sigchain.

Signed-off-by: Xia XiaoWen <haoyurenzhuxia@xxxxxxxxx>
---
 midx.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/midx.c b/midx.c
index 5f0dd386b0..6586051a62 100644
--- a/midx.c
+++ b/midx.c
@@ -17,6 +17,7 @@
 #include "refs.h"
 #include "revision.h"
 #include "list-objects.h"
+#include "sigchain.h"
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
@@ -41,6 +42,8 @@
 
 #define PACK_EXPIRED UINT_MAX
 
+static struct strbuf rev_filename = STRBUF_INIT;
+
 const unsigned char *get_midx_checksum(struct multi_pack_index *m)
 {
 	return m->data + m->data_len - the_hash_algo->rawsz;
@@ -884,21 +887,29 @@ static uint32_t *midx_pack_order(struct write_midx_context *ctx)
 	return pack_order;
 }
 
+static void remove_rev_file_on_signal(int signo)
+{
+	if (unlink(rev_filename.buf))
+		die_errno(_("failed to remove %s"), rev_filename.buf);
+
+	sigchain_pop(signo);
+	raise(signo);
+}
+
 static void write_midx_reverse_index(char *midx_name, unsigned char *midx_hash,
 				     struct write_midx_context *ctx)
 {
-	struct strbuf buf = STRBUF_INIT;
 	const char *tmp_file;
 
-	strbuf_addf(&buf, "%s-%s.rev", midx_name, hash_to_hex(midx_hash));
+	strbuf_addf(&rev_filename, "%s-%s.rev", midx_name, hash_to_hex(midx_hash));
 
 	tmp_file = write_rev_file_order(NULL, ctx->pack_order, ctx->entries_nr,
 					midx_hash, WRITE_REV);
 
-	if (finalize_object_file(tmp_file, buf.buf))
+	if (finalize_object_file(tmp_file, rev_filename.buf))
 		die(_("cannot store reverse index file"));
 
-	strbuf_release(&buf);
+	sigchain_push_common(remove_rev_file_on_signal);
 }
 
 static void clear_midx_files_ext(const char *object_dir, const char *ext,
-- 
2.34.1.52.g9efd6505a3.dirty.agit.6.5.6