commit 30a624fb1ef8d2d9706a604cbf65dcdacf072e72
from: Stefan Sperling <stsp@stsp.name>
date: Tue Mar 19 13:36:57 2024 UTC

avoid a rename/stat race when gotd installs a new pack and then uses it

Reset the cached repository's pack directory mtime after installing a new
pack and pack index file. I have observed the mtime of the pack directory
as reported by stat(2) remaining unchanged, until some time has passed
beyond the rename(2) calls used to install the pack file and its index.

If gotd immediately tries to read objects installed in a new pack file then
the mtime reported by stat(2) might appear as unchanged. gotd will then fail
to update its cached list of pack index files and not find the newly
installed objects.
Clearing the cached timestamp forces a readdir(3) call which does expose
the newly installed pack index file as expected.

Not sure whether stat(2) is supposed to immediately expose mtime changes
after a rename(2). If so then this might warrant digging into the kernel.

Seen while running regression tests for upcoming gotd notification support.

commit - 10477b5aacb13088676c3bfd7e0fcc477ba2724e
commit + 30a624fb1ef8d2d9706a604cbf65dcdacf072e72
blob - ed6de8db29817b25f285cd13c8395a03bfa2e2aa
blob + 6c4441cc4454a3e740e917e1c8cf70fb2764235c
--- gotd/repo_write.c
+++ gotd/repo_write.c
@@ -1715,6 +1715,12 @@ repo_write_dispatch_session(int fd, short event, void 
 					    err->msg);
 					break;
 				}
+				/*
+				 * Ensure we re-read the pack index list
+				 * upon next access.
+				 */
+				repo_write.repo->pack_path_mtime.tv_sec = 0;
+				repo_write.repo->pack_path_mtime.tv_nsec = 0;
 			}
 			err = update_refs(iev);
 			if (err) {
blob - b0b449ab2c4db803b92e006427b500772b2d2e55
blob + d67328a67243a5beff513f9e3feeb89708060657
--- gotd/session.c
+++ gotd/session.c
@@ -366,6 +366,10 @@ install_pack(struct gotd_session_client *client, const
 		    packidx_path);
 		goto done;
 	}
+
+	/* Ensure we re-read the pack index list upon next access. */
+	gotd_session.repo->pack_path_mtime.tv_sec = 0;
+	gotd_session.repo->pack_path_mtime.tv_nsec = 0;
 
 	free(client->packidx_path);
 	client->packidx_path = NULL;