On Mon, Oct 7, 2019 at 1:08 PM Derrick Stolee via GitGitGadget
<gitgitgadget@xxxxxxxxx> wrote:
>
> From: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
>
> If two 'git sparse-checkout set' subcommands are launched at the
> same time, the behavior can be unexpected as they compete to write
> the sparse-checkout file and update the working directory.
>
> Take a lockfile around the writes to the sparse-checkout file. In
> addition, acquire this lock around the working directory update
> to avoid two commands updating the working directory in different
> ways.
Wow, there's something I never would have thought to check. Did you
have folks run into this, or is this just some defensive programming?
Either way, I'm impressed.
>
> Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
> ---
> builtin/sparse-checkout.c | 15 ++++++++++++---
> t/t1091-sparse-checkout-builtin.sh | 7 +++++++
> 2 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
> index 542d57fac6..9b313093cd 100644
> --- a/builtin/sparse-checkout.c
> +++ b/builtin/sparse-checkout.c
> @@ -308,6 +308,8 @@ static int write_patterns_and_update(struct pattern_list *pl)
> {
> char *sparse_filename;
> FILE *fp;
> + int fd;
> + struct lock_file lk = LOCK_INIT;
> int result;
>
> if (!core_apply_sparse_checkout) {
> @@ -317,21 +319,28 @@ static int write_patterns_and_update(struct pattern_list *pl)
>
> result = update_working_directory(pl);
>
> + sparse_filename = get_sparse_checkout_filename();
> + fd = hold_lock_file_for_update(&lk, sparse_filename,
> + LOCK_DIE_ON_ERROR);
> +
> + result = update_working_directory(pl);
> if (result) {
> + rollback_lock_file(&lk);
> + free(sparse_filename);
> clear_pattern_list(pl);
> update_working_directory(NULL);
> return result;
> }
>
> - sparse_filename = get_sparse_checkout_filename();
> - fp = fopen(sparse_filename, "w");
> + fp = fdopen(fd, "w");
>
> if (core_sparse_checkout_cone)
> write_cone_to_file(fp, pl);
> else
> write_patterns_to_file(fp, pl);
>
> - fclose(fp);
> + fflush(fp);
> + commit_lock_file(&lk);
>
> free(sparse_filename);
> clear_pattern_list(pl);
> diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
> index 82eb5fb2f8..f22a4afbea 100755
> --- a/t/t1091-sparse-checkout-builtin.sh
> +++ b/t/t1091-sparse-checkout-builtin.sh
> @@ -262,4 +262,11 @@ test_expect_success 'revert to old sparse-checkout on bad update' '
> test_cmp dir expect
> '
>
> +test_expect_success 'fail when lock is taken' '
> + test_when_finished rm -rf repo/.git/info/sparse-checkout.lock &&
> + touch repo/.git/info/sparse-checkout.lock &&
> + test_must_fail git -C repo sparse-checkout set deep 2>err &&
> + test_i18ngrep "File exists" err
> +'
> +
> test_done
> --
> gitgitgadget
>
