> From: Han-Wen Nienhuys <hanwen@xxxxxxxxxx> > > Errno is a global variable written by almost all system calls, and therefore it > is hard to reason about its state. It's also useless for user-visible errors, as > it leaves no place to report the offending file and/or syscall. I don't think this paragraph is useful. > For the copy/rename support, calls to lock_ref_oid_basic() in this file are > followed by: > > * lock_ref_oid_basic (copy/rename rollback error path) > > * write_ref_to_lockfile (both in the rollback path and the success path of > copy/rename) > > These calls do not inspect the incoming errno. As they perform I/O, they can > clobber errno. For this reason, callers cannot reliably observe the errno that > lock_ref_oid_basic() generated, so it is unsound for programmatic use. > > For files_create_symref() and files_reflog_expire(), grepping over callers > showed no callers inspecting errno. This is probably written more clearly as follows: No call to the static function lock_ref_oid_basic() is immediately followed by an errno check, so stopping setting errno is safe. But as a sanity check, lock_ref_oid_basic() is used in these functions: - files_copy_or_rename_ref() - here, calls are followed by error() (which performs I/O) or write_ref_to_lockfile() (which calls parse_object() which may perform I/O) - files_create_symref() - here, calls are followed by error() or create_symref_locked() (which performs I/O and does not inspect errno) - files_reflog_expire() - here, calls are followed by error() or refs_reflog_exists() (which calls a function in a vtable that is not documented to use and/or preserve errno) So it is safe to stop setting errno in lock_ref_oid_basic(). The diff itself looks good.
