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[v2,3/9] pack-write: refactor renaming in finish_tmp_packfile()

Message ID 2e907e309de6804c329a9efb6a6d89fb318683f3.1631228928.git.me@ttaylorr.com (mailing list archive)
State Accepted
Commit 66833f0e70c473ca6c4e6a79d34e879d8b40ba9d
Headers show
Series packfile: avoid .idx rename races | expand

Commit Message

Taylor Blau Sept. 9, 2021, 11:24 p.m. UTC 
From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>

Refactor the renaming in finish_tmp_packfile() into a helper function.
The callers are now expected to pass a "name_buffer" ending in
"pack-OID." instead of the previous "pack-", we then append "pack",
"idx" or "rev" to it.

By doing the strbuf_setlen() in rename_tmp_packfile() we reuse the
buffer and avoid the repeated allocations we'd get if that function had
its own temporary "struct strbuf".

This approach of reusing the buffer does make the last user in
pack-object.c's write_pack_file() slightly awkward, since we needlessly
do a strbuf_setlen() before calling strbuf_release() for consistency. In
subsequent changes we'll move that bitmap writing code around, so let's
not skip the strbuf_setlen() now.

The previous strbuf_reset() idiom originated with 5889271114a
(finish_tmp_packfile():use strbuf for pathname construction,
2014-03-03), which in turn was a minimal adjustment of pre-strbuf code
added in 0e990530ae (finish_tmp_packfile(): a helper function,
2011-10-28).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 builtin/pack-objects.c |  7 +++++--
 bulk-checkin.c         |  3 ++-
 pack-write.c           | 37 ++++++++++++++++---------------------
 3 files changed, 23 insertions(+), 24 deletions(-)
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Patch

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index df49f656b9..2a105c8d6e 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1237,7 +1237,8 @@  static void write_pack_file(void)
 					warning_errno(_("failed utime() on %s"), pack_tmp_name);
 			}
 
-			strbuf_addf(&tmpname, "%s-", base_name);
+			strbuf_addf(&tmpname, "%s-%s.", base_name,
+				    hash_to_hex(hash));
 
 			if (write_bitmap_index) {
 				bitmap_writer_set_checksum(hash);
@@ -1250,8 +1251,9 @@  static void write_pack_file(void)
 					    &pack_idx_opts, hash);
 
 			if (write_bitmap_index) {
-				strbuf_addf(&tmpname, "%s.bitmap", hash_to_hex(hash));
+				size_t tmpname_len = tmpname.len;
 
+				strbuf_addstr(&tmpname, "bitmap");
 				stop_progress(&progress_state);
 
 				bitmap_writer_show_progress(progress);
@@ -1260,6 +1262,7 @@  static void write_pack_file(void)
 				bitmap_writer_finish(written_list, nr_written,
 						     tmpname.buf, write_bitmap_options);
 				write_bitmap_index = 0;
+				strbuf_setlen(&tmpname, tmpname_len);
 			}
 
 			strbuf_release(&tmpname);
diff --git a/bulk-checkin.c b/bulk-checkin.c
index 6283bc8bd9..c19d471f0b 100644
--- a/bulk-checkin.c
+++ b/bulk-checkin.c
@@ -46,7 +46,8 @@  static void finish_bulk_checkin(struct bulk_checkin_state *state)
 		close(fd);
 	}
 
-	strbuf_addf(&packname, "%s/pack/pack-", get_object_directory());
+	strbuf_addf(&packname, "%s/pack/pack-%s.", get_object_directory(),
+		    hash_to_hex(hash));
 	finish_tmp_packfile(&packname, state->pack_tmp_name,
 			    state->written, state->nr_written,
 			    &state->pack_idx_opts, hash);
diff --git a/pack-write.c b/pack-write.c
index 2767b78619..58bc5fbcdf 100644
--- a/pack-write.c
+++ b/pack-write.c
@@ -458,6 +458,18 @@  struct hashfile *create_tmp_packfile(char **pack_tmp_name)
 	return hashfd(fd, *pack_tmp_name);
 }
 
+static void rename_tmp_packfile(struct strbuf *name_prefix, const char *source,
+				const char *ext)
+{
+	size_t name_prefix_len = name_prefix->len;
+
+	strbuf_addstr(name_prefix, ext);
+	if (rename(source, name_prefix->buf))
+		die_errno("unable to rename temporary file to '%s'",
+			  name_prefix->buf);
+	strbuf_setlen(name_prefix, name_prefix_len);
+}
+
 void finish_tmp_packfile(struct strbuf *name_buffer,
 			 const char *pack_tmp_name,
 			 struct pack_idx_entry **written_list,
@@ -466,7 +478,6 @@  void finish_tmp_packfile(struct strbuf *name_buffer,
 			 unsigned char hash[])
 {
 	const char *idx_tmp_name, *rev_tmp_name = NULL;
-	int basename_len = name_buffer->len;
 
 	if (adjust_shared_perm(pack_tmp_name))
 		die_errno("unable to make temporary pack file readable");
@@ -479,26 +490,10 @@  void finish_tmp_packfile(struct strbuf *name_buffer,
 	rev_tmp_name = write_rev_file(NULL, written_list, nr_written, hash,
 				      pack_idx_opts->flags);
 
-	strbuf_addf(name_buffer, "%s.pack", hash_to_hex(hash));
-
-	if (rename(pack_tmp_name, name_buffer->buf))
-		die_errno("unable to rename temporary pack file");
-
-	strbuf_setlen(name_buffer, basename_len);
-
-	strbuf_addf(name_buffer, "%s.idx", hash_to_hex(hash));
-	if (rename(idx_tmp_name, name_buffer->buf))
-		die_errno("unable to rename temporary index file");
-
-	strbuf_setlen(name_buffer, basename_len);
-
-	if (rev_tmp_name) {
-		strbuf_addf(name_buffer, "%s.rev", hash_to_hex(hash));
-		if (rename(rev_tmp_name, name_buffer->buf))
-			die_errno("unable to rename temporary reverse-index file");
-	}
-
-	strbuf_setlen(name_buffer, basename_len);
+	rename_tmp_packfile(name_buffer, pack_tmp_name, "pack");
+	rename_tmp_packfile(name_buffer, idx_tmp_name, "idx");
+	if (rev_tmp_name)
+		rename_tmp_packfile(name_buffer, rev_tmp_name, "rev");
 
 	free((void *)idx_tmp_name);
 }