Re: [PATCH 2/8] refs/files-backend: stop setting errno from lock_ref_oid_basic

> > 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.

> 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().