From: Junio C Hamano <gitster@pobox.com>
To: "Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Han-Wen Nienhuys <hanwenn@gmail.com>,
Han-Wen Nienhuys <hanwen@google.com>
Subject: Re: [PATCH 2/8] refs/files-backend: stop setting errno from lock_ref_oid_basic
Date: Fri, 30 Apr 2021 12:10:43 +0900 [thread overview]
Message-ID: <xmqqbl9weabw.fsf@gitster.g> (raw)
In-Reply-To: <b2c72097e5e8985e7fdd8e3eee66cdf43d1b65c0.1619710329.git.gitgitgadget@gmail.com> (Han-Wen Nienhuys via GitGitGadget's message of "Thu, 29 Apr 2021 15:32:02 +0000")
I 100% agree with you that errno is cumbersome to use and carries
far less information than we want (we do not learn what operation
failed on what path) over a long distance. It only is useful when
the callchain still knows what path was operated on.
But...
"Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 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.
In the latter part of the above, "callers" refers to the callers of
"the copy/rename support" (aka files_copy_or_rename_ref())?
Then I am not sure why "callers cannot reliably observe the errno
that lock_ref_oid_basic() generated" is a problem. They will see
the errno from the last system call that failed, if they care. So
their performing I/O is perfectly acceptable, too.
Hence, I am not sure what change the above justifies, if any.
If we can show that no caller of files_copy_or_rename_ref() uses
errno, it is a clear indication that lock_ref_oid_basic() is saving
and restoring errno for no good reason. I think that is what was
done for the other two callers below.
So I traced what happens after the copy-rename thing gets called.
refs_rename_ref(), rename_ref(), refs_copy_existing_ref() and
copy_existing_ref() (all in refs.c) should be the only callers of
the function. All callers in builtin/branch.c and builtin/remote.c
of these functions (by the way, refs_X() variants do not seem to be
called from anywhere---are they over-engineered?) just die() when
they signal a failure by returning non-zero, so I think it is safe
and much easier to understand to justify this change like so:
refs/files-backend.c::lock_ref_oid_basic() tries hard to signal
how it failed to its callers using errno. The three callers of
this file-scope static function are
* files_copy_or_rename_ref()
* files_create_symref()
* files_reflog_expire()
None of them looks at errno after seeing a negative return from
lock_ref_oid_basic() to make any decision, and no caller of
these three functions looks at errno after they signal a failure
by returning a negative value.
> For files_create_symref() and files_reflog_expire(), grepping over callers
> showed no callers inspecting errno.
Yes, this is a lot more relevant justification to allow these two
functions, and functions that are called _only_ _by_ these two
functions, stop worrying about errno.
next prev parent reply other threads:[~2021-04-30 3:10 UTC|newest]
Thread overview: 148+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 15:32 [PATCH 0/8] refs: cleanup errno sideband ref related functions Han-Wen Nienhuys via GitGitGadget
2021-04-29 15:32 ` [PATCH 1/8] refs: remove EINVAL specification from the errno sideband in read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-04-30 2:38 ` Junio C Hamano
2021-05-19 12:25 ` Han-Wen Nienhuys
2021-06-03 2:19 ` Jonathan Tan
2021-06-09 11:28 ` Han-Wen Nienhuys
2021-04-29 15:32 ` [PATCH 2/8] refs/files-backend: stop setting errno from lock_ref_oid_basic Han-Wen Nienhuys via GitGitGadget
2021-04-30 3:10 ` Junio C Hamano [this message]
2021-05-19 12:29 ` Han-Wen Nienhuys
2021-06-03 2:33 ` Jonathan Tan
2021-06-10 10:02 ` Han-Wen Nienhuys
2021-04-29 15:32 ` [PATCH 3/8] refs: make errno output explicit for read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-04-30 3:34 ` Junio C Hamano
2021-04-30 6:02 ` Junio C Hamano
2021-05-19 12:33 ` Han-Wen Nienhuys
2021-06-03 2:37 ` Jonathan Tan
2021-06-10 10:05 ` Han-Wen Nienhuys
2021-04-29 15:32 ` [PATCH 4/8] refs: make errno output explicit for refs_resolve_ref_unsafe Han-Wen Nienhuys via GitGitGadget
2021-06-03 2:51 ` Jonathan Tan
2021-06-10 11:27 ` Han-Wen Nienhuys
2021-04-29 15:32 ` [PATCH 5/8] refs: add failure_errno to refs_read_raw_ref() signature Han-Wen Nienhuys via GitGitGadget
2021-04-29 15:32 ` [PATCH 6/8] refs: clear errno return in refs_resolve_ref_unsafe() Han-Wen Nienhuys via GitGitGadget
2021-06-03 2:53 ` Jonathan Tan
2021-06-10 11:45 ` Han-Wen Nienhuys
2021-04-29 15:32 ` [PATCH 7/8] refs: stop setting EINVAL and ELOOP in symref resolution Han-Wen Nienhuys via GitGitGadget
2021-06-03 2:55 ` Jonathan Tan
2021-06-10 11:58 ` Han-Wen Nienhuys
2021-04-29 15:32 ` [PATCH 8/8] refs: explicitly propagate errno from refs_read_raw_ref Han-Wen Nienhuys via GitGitGadget
2021-06-03 2:13 ` [PATCH 0/8] refs: cleanup errno sideband ref related functions Jonathan Tan
2021-06-09 11:29 ` Han-Wen Nienhuys
2021-06-10 12:57 ` [PATCH v2 " Han-Wen Nienhuys via GitGitGadget
2021-06-10 12:57 ` [PATCH v2 1/8] refs: remove EINVAL errno output from specification of read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-06-10 12:57 ` [PATCH v2 2/8] refs/files-backend: stop setting errno from lock_ref_oid_basic Han-Wen Nienhuys via GitGitGadget
2021-07-01 11:13 ` Ævar Arnfjörð Bjarmason
2021-07-05 14:16 ` Han-Wen Nienhuys
2021-06-10 12:57 ` [PATCH v2 3/8] refs: make errno output explicit for read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-07-01 11:34 ` Ævar Arnfjörð Bjarmason
2021-07-05 14:34 ` Han-Wen Nienhuys
2021-06-10 12:57 ` [PATCH v2 4/8] refs: make errno output explicit for refs_resolve_ref_unsafe Han-Wen Nienhuys via GitGitGadget
2021-07-01 11:56 ` Ævar Arnfjörð Bjarmason
2021-06-10 12:57 ` [PATCH v2 5/8] refs: use refs_resolve_ref_unsafe_with_errno() where needed Han-Wen Nienhuys via GitGitGadget
2021-07-01 11:58 ` Ævar Arnfjörð Bjarmason
2021-06-10 12:57 ` [PATCH v2 6/8] refs: add failure_errno to refs_read_raw_ref() signature Han-Wen Nienhuys via GitGitGadget
2021-07-01 12:06 ` Ævar Arnfjörð Bjarmason
2021-06-10 12:57 ` [PATCH v2 7/8] refs: clear errno return in refs_resolve_ref_unsafe() Han-Wen Nienhuys via GitGitGadget
2021-07-01 12:19 ` Ævar Arnfjörð Bjarmason
2021-06-10 12:57 ` [PATCH v2 8/8] refs: explicitly propagate errno from refs_read_raw_ref Han-Wen Nienhuys via GitGitGadget
2021-07-01 12:26 ` Ævar Arnfjörð Bjarmason
2021-07-05 16:09 ` Han-Wen Nienhuys
2021-07-05 19:08 ` Ævar Arnfjörð Bjarmason
2021-07-05 19:39 ` Han-Wen Nienhuys
2021-06-14 10:10 ` [PATCH v2 0/8] refs: cleanup errno sideband ref related functions Han-Wen Nienhuys
2021-07-05 20:56 ` [PATCH v3 0/5] " Han-Wen Nienhuys via GitGitGadget
2021-07-05 20:56 ` [PATCH v3 1/5] refs: remove EINVAL errno output from specification of read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-07-05 20:56 ` [PATCH v3 2/5] refs/files-backend: stop setting errno from lock_ref_oid_basic Han-Wen Nienhuys via GitGitGadget
2021-07-05 20:56 ` [PATCH v3 3/5] refs: make errno output explicit for read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-07-05 20:56 ` [PATCH v3 4/5] refs: add failure_errno to refs_read_raw_ref() signature Han-Wen Nienhuys via GitGitGadget
2021-07-06 19:28 ` Junio C Hamano
2021-07-05 20:56 ` [PATCH v3 5/5] refs: make errno output explicit for refs_resolve_ref_unsafe Han-Wen Nienhuys via GitGitGadget
2021-07-06 0:38 ` [PATCH v3 0/5] refs: cleanup errno sideband ref related functions Ævar Arnfjörð Bjarmason
2021-07-06 9:53 ` Han-Wen Nienhuys
2021-07-06 14:27 ` Ævar Arnfjörð Bjarmason
2021-07-06 18:36 ` Han-Wen Nienhuys
2021-07-06 18:55 ` [PATCH v4 0/6] " Han-Wen Nienhuys via GitGitGadget
2021-07-06 18:55 ` [PATCH v4 1/6] refs: remove EINVAL errno output from specification of read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-07-06 18:55 ` [PATCH v4 2/6] refs/files-backend: stop setting errno from lock_ref_oid_basic Han-Wen Nienhuys via GitGitGadget
2021-07-06 18:55 ` [PATCH v4 3/6] refs: make errno output explicit for read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-07-06 18:55 ` [PATCH v4 4/6] refs: add failure_errno to refs_read_raw_ref() signature Han-Wen Nienhuys via GitGitGadget
2021-07-06 19:39 ` Junio C Hamano
2021-07-06 18:55 ` [PATCH v4 5/6] refs: explicitly return failure_errno from parse_loose_ref_contents Han-Wen Nienhuys via GitGitGadget
2021-07-06 19:37 ` Junio C Hamano
2021-07-07 8:20 ` Han-Wen Nienhuys
2021-07-06 18:55 ` [PATCH v4 6/6] refs: make errno output explicit for refs_resolve_ref_unsafe Han-Wen Nienhuys via GitGitGadget
2021-07-07 19:07 ` [PATCH v5 0/6] refs: cleanup errno sideband ref related functions Han-Wen Nienhuys via GitGitGadget
2021-07-07 19:07 ` [PATCH v5 1/6] refs: remove EINVAL errno output from specification of read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-07-07 19:07 ` [PATCH v5 2/6] refs/files-backend: stop setting errno from lock_ref_oid_basic Han-Wen Nienhuys via GitGitGadget
2021-07-11 11:38 ` Ævar Arnfjörð Bjarmason
2021-07-13 8:00 ` Han-Wen Nienhuys
2021-07-07 19:07 ` [PATCH v5 3/6] refs: make errno output explicit for read_raw_ref_fn Han-Wen Nienhuys via GitGitGadget
2021-07-11 11:52 ` Ævar Arnfjörð Bjarmason
2021-07-07 19:07 ` [PATCH v5 4/6] refs: add failure_errno to refs_read_raw_ref() signature Han-Wen Nienhuys via GitGitGadget
2021-07-11 11:59 ` Ævar Arnfjörð Bjarmason
2021-07-13 8:02 ` Han-Wen Nienhuys
2021-07-07 19:07 ` [PATCH v5 5/6] refs: explicitly return failure_errno from parse_loose_ref_contents Han-Wen Nienhuys via GitGitGadget
2021-07-11 12:41 ` Ævar Arnfjörð Bjarmason
2021-07-07 19:07 ` [PATCH v5 6/6] refs: make errno output explicit for refs_resolve_ref_unsafe Han-Wen Nienhuys via GitGitGadget
2021-07-07 20:44 ` [PATCH v5 0/6] refs: cleanup errno sideband ref related functions Junio C Hamano
2021-07-11 16:30 ` [PATCH v6? 00/17] refs API: get rid of errno setting entirely Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 01/17] refs: remove EINVAL errno output from specification of read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 02/17] refs/files-backend: stop setting errno from lock_ref_oid_basic Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 03/17] refs: make errno output explicit for read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 04/17] refs: add failure_errno to refs_read_raw_ref() signature Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 05/17] refs: explicitly return failure_errno from parse_loose_ref_contents Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 06/17] refs: make errno output explicit for refs_resolve_ref_unsafe Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 07/17] refs: make errno ignoring explicit in lock_ref_oid_basic() Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 08/17] refs file-backend.c: stop setting "EBUSY" in verify_lock() Ævar Arnfjörð Bjarmason
2021-07-13 8:08 ` Han-Wen Nienhuys
2021-07-11 16:30 ` [PATCH v6? 09/17] refs file-backend.c: deal with errno directly " Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 10/17] refs API: remove refs_read_ref_full() wrapper Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 11/17] refs API: make resolve_gitlink_ref() not set errno Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 12/17] refs API: make refs_resolve_ref_unsafe() static Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 13/17] refs API: make refs_resolve_refdup() not set errno Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 14/17] refs API: make refs_ref_exists() " Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 15/17] refs API: make resolve_ref_unsafe() " Ævar Arnfjörð Bjarmason
2021-07-13 8:13 ` Han-Wen Nienhuys
2021-07-14 8:32 ` Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 16/17] refs API: make expand_ref() and repo_dwim_log() " Ævar Arnfjörð Bjarmason
2021-07-11 16:30 ` [PATCH v6? 17/17] refs API: don't leak "errno" in run_transaction_hook() Ævar Arnfjörð Bjarmason
2021-07-13 8:28 ` [PATCH v6? 00/17] refs API: get rid of errno setting entirely Han-Wen Nienhuys
2021-07-13 18:26 ` Ævar Arnfjörð Bjarmason
2021-07-14 8:38 ` Ævar Arnfjörð Bjarmason
2021-07-14 8:43 ` Han-Wen Nienhuys
2021-07-14 11:43 ` [PATCH v7 0/6] refs: cleanup errno sideband ref related functions Ævar Arnfjörð Bjarmason
2021-07-14 11:43 ` [PATCH v7 1/6] refs: remove EINVAL errno output from specification of read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-07-14 11:43 ` [PATCH v7 2/6] refs/files-backend: stop setting errno from lock_ref_oid_basic Ævar Arnfjörð Bjarmason
2021-07-14 11:43 ` [PATCH v7 3/6] refs: make errno output explicit for read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-07-14 11:43 ` [PATCH v7 4/6] refs: add failure_errno to refs_read_raw_ref() signature Ævar Arnfjörð Bjarmason
2021-07-14 11:43 ` [PATCH v7 5/6] refs: explicitly return failure_errno from parse_loose_ref_contents Ævar Arnfjörð Bjarmason
2021-07-14 11:43 ` [PATCH v7 6/6] refs: make errno output explicit for refs_resolve_ref_unsafe Ævar Arnfjörð Bjarmason
2021-07-16 14:22 ` [PATCH v8 0/7] refs: cleanup errno sideband ref related functions Ævar Arnfjörð Bjarmason
2021-07-16 14:22 ` [PATCH v8 1/7] refs file backend: move raceproof_create_file() here Ævar Arnfjörð Bjarmason
2021-07-16 14:22 ` [PATCH v8 2/7] refs: remove EINVAL errno output from specification of read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-07-16 14:22 ` [PATCH v8 3/7] refs/files-backend: stop setting errno from lock_ref_oid_basic Ævar Arnfjörð Bjarmason
2021-07-16 14:22 ` [PATCH v8 4/7] refs: make errno output explicit for read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-07-16 14:22 ` [PATCH v8 5/7] refs: add failure_errno to refs_read_raw_ref() signature Ævar Arnfjörð Bjarmason
2021-07-16 14:22 ` [PATCH v8 6/7] refs: explicitly return failure_errno from parse_loose_ref_contents Ævar Arnfjörð Bjarmason
2021-07-16 14:22 ` [PATCH v8 7/7] refs: make errno output explicit for refs_resolve_ref_unsafe Ævar Arnfjörð Bjarmason
2021-07-20 10:33 ` [PATCH v9 0/7] refs: cleanup errno sideband ref related functions Ævar Arnfjörð Bjarmason
2021-07-20 10:33 ` [PATCH v9 1/7] refs file backend: move raceproof_create_file() here Ævar Arnfjörð Bjarmason
2021-07-20 10:33 ` [PATCH v9 2/7] refs: remove EINVAL errno output from specification of read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-07-20 10:33 ` [PATCH v9 3/7] refs/files-backend: stop setting errno from lock_ref_oid_basic Ævar Arnfjörð Bjarmason
2021-07-20 10:33 ` [PATCH v9 4/7] refs: make errno output explicit for read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-08-16 13:00 ` Han-Wen Nienhuys
2021-07-20 10:33 ` [PATCH v9 5/7] refs: add failure_errno to refs_read_raw_ref() signature Ævar Arnfjörð Bjarmason
2021-07-20 10:33 ` [PATCH v9 6/7] refs: explicitly return failure_errno from parse_loose_ref_contents Ævar Arnfjörð Bjarmason
2021-08-13 20:54 ` Jonathan Tan
2021-07-20 10:33 ` [PATCH v9 7/7] refs: make errno output explicit for refs_resolve_ref_unsafe Ævar Arnfjörð Bjarmason
2021-07-26 23:49 ` [PATCH v9 0/7] refs: cleanup errno sideband ref related functions Ævar Arnfjörð Bjarmason
2021-07-27 0:18 ` Junio C Hamano
2021-08-23 11:52 ` [PATCH v10 0/8] " Ævar Arnfjörð Bjarmason
2021-08-23 11:52 ` [PATCH v10 1/8] refs file backend: move raceproof_create_file() here Ævar Arnfjörð Bjarmason
2021-08-23 11:52 ` [PATCH v10 2/8] refs: remove EINVAL errno output from specification of read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-08-23 11:52 ` [PATCH v10 3/8] refs/files-backend: stop setting errno from lock_ref_oid_basic Ævar Arnfjörð Bjarmason
2021-08-23 11:52 ` [PATCH v10 4/8] refs: make errno output explicit for read_raw_ref_fn Ævar Arnfjörð Bjarmason
2021-08-23 11:52 ` [PATCH v10 5/8] refs: add failure_errno to refs_read_raw_ref() signature Ævar Arnfjörð Bjarmason
2021-08-23 11:52 ` [PATCH v10 6/8] branch tests: test for errno propagating on failing read Ævar Arnfjörð Bjarmason
2021-08-23 11:52 ` [PATCH v10 7/8] refs: explicitly return failure_errno from parse_loose_ref_contents Ævar Arnfjörð Bjarmason
2021-08-23 11:52 ` [PATCH v10 8/8] refs: make errno output explicit for refs_resolve_ref_unsafe Ævar Arnfjörð Bjarmason
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