[PATCH v7 4/6] refs: add failure_errno to refs_read_raw_ref() signature

From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>, "Jeff King" <peff@peff.net>,
	"Han-Wen Nienhuys" <hanwen@google.com>,
	"Michael Haggerty" <mhagger@alum.mit.edu>,
	"Jonathan Tan" <jonathantanmy@google.com>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: [PATCH v7 4/6] refs: add failure_errno to refs_read_raw_ref() signature
Date: Wed, 14 Jul 2021 13:43:32 +0200	[thread overview]
Message-ID: <patch-4.6-dd191768f6-20210714T114301Z-avarab@gmail.com> (raw)
In-Reply-To: <cover-0.6-0000000000-20210714T114301Z-avarab@gmail.com>

From: Han-Wen Nienhuys <hanwen@google.com>

This lets us use the explicit errno output parameter in refs_resolve_ref_unsafe.

Some of our callers explicitly do not care about the errno, rather
than understanding NULL let's have them declare that they don't care
by passing in an "ignore_errno". There's only three of them, and using
that pattern will make it more obvious that they want to throw away
data, let's also add a comment to one of the callers about why we'd
like to ignore the errno.

Let's not extend that to refs_resolve_ref_unsafe() itself for now, it
has a large set of legacy callers, so we're faking up the old "errno"
behavior for it. We can convert those callers to
refs_resolve_ref_unsafe_with_errno() later.

We are leaving out out the refs_read_special_head() in
refs_read_raw_ref() for now, as noted in the next commit moving it to
"failure_errno" will require some special consideration.

We're intentionally mis-indenting the argument list of the new
refs_resolve_ref_unsafe_with_errno(), it will be non-static in a
subsequent commit, doing it this way makes that diff smaller.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 refs.c                | 61 ++++++++++++++++++++++++++++++-------------
 refs/files-backend.c  | 10 ++++---
 refs/packed-backend.c |  7 ++---
 refs/refs-internal.h  |  6 ++---
 4 files changed, 56 insertions(+), 28 deletions(-)

diff --git a/refs.c b/refs.c
index 7b3f05a66f..406e27213b 100644
--- a/refs.c
+++ b/refs.c
@@ -1671,30 +1671,33 @@ static int refs_read_special_head(struct ref_store *ref_store,
 	return result;
 }
 
-int refs_read_raw_ref(struct ref_store *ref_store,
-		      const char *refname, struct object_id *oid,
-		      struct strbuf *referent, unsigned int *type)
+int refs_read_raw_ref(struct ref_store *ref_store, const char *refname,
+		      struct object_id *oid, struct strbuf *referent,
+		      unsigned int *type, int *failure_errno)
 {
+	assert(failure_errno);
 	if (!strcmp(refname, "FETCH_HEAD") || !strcmp(refname, "MERGE_HEAD")) {
 		return refs_read_special_head(ref_store, refname, oid, referent,
 					      type);
 	}
 
 	return ref_store->be->read_raw_ref(ref_store, refname, oid, referent,
-					   type, &errno);
+					   type, failure_errno);
 }
 
-/* This function needs to return a meaningful errno on failure */
-const char *refs_resolve_ref_unsafe(struct ref_store *refs,
-				    const char *refname,
-				    int resolve_flags,
-				    struct object_id *oid, int *flags)
+static const char *refs_resolve_ref_unsafe_with_errno(struct ref_store *refs,
+					       const char *refname,
+					       int resolve_flags,
+					       struct object_id *oid,
+					       int *flags, int *failure_errno)
 {
 	static struct strbuf sb_refname = STRBUF_INIT;
 	struct object_id unused_oid;
 	int unused_flags;
 	int symref_count;
 
+	assert(failure_errno);
+
 	if (!oid)
 		oid = &unused_oid;
 	if (!flags)
@@ -1705,7 +1708,7 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 	if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
 		if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
 		    !refname_is_safe(refname)) {
-			errno = EINVAL;
+			*failure_errno = EINVAL;
 			return NULL;
 		}
 
@@ -1723,8 +1726,8 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 	for (symref_count = 0; symref_count < SYMREF_MAXDEPTH; symref_count++) {
 		unsigned int read_flags = 0;
 
-		if (refs_read_raw_ref(refs, refname,
-				      oid, &sb_refname, &read_flags)) {
+		if (refs_read_raw_ref(refs, refname, oid, &sb_refname,
+				      &read_flags, failure_errno)) {
 			*flags |= read_flags;
 
 			/* In reading mode, refs must eventually resolve */
@@ -1736,9 +1739,9 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 			 * may show errors besides ENOENT if there are
 			 * similarly-named refs.
 			 */
-			if (errno != ENOENT &&
-			    errno != EISDIR &&
-			    errno != ENOTDIR)
+			if (*failure_errno != ENOENT &&
+			    *failure_errno != EISDIR &&
+			    *failure_errno != ENOTDIR)
 				return NULL;
 
 			oidclr(oid);
@@ -1765,7 +1768,7 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 		if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
 			if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
 			    !refname_is_safe(refname)) {
-				errno = EINVAL;
+				*failure_errno = EINVAL;
 				return NULL;
 			}
 
@@ -1773,10 +1776,24 @@ const char *refs_resolve_ref_unsafe(struct ref_store *refs,
 		}
 	}
 
-	errno = ELOOP;
+	*failure_errno = ELOOP;
 	return NULL;
 }
 
+const char *refs_resolve_ref_unsafe(struct ref_store *refs, const char *refname,
+				    int resolve_flags, struct object_id *oid,
+				    int *flags)
+{
+	int failure_errno = 0;
+	const char *refn;
+	refn = refs_resolve_ref_unsafe_with_errno(refs, refname, resolve_flags,
+						  oid, flags, &failure_errno);
+	if (!refn)
+		/* For unmigrated legacy callers */
+		errno = failure_errno;
+	return refn;
+}
+
 /* backend functions */
 int refs_init_db(struct strbuf *err)
 {
@@ -2227,6 +2244,13 @@ int refs_verify_refname_available(struct ref_store *refs,
 
 	strbuf_grow(&dirname, strlen(refname) + 1);
 	for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
+		/*
+		 * Just saying "Is a directory" when we e.g. can't
+		 * lock some multi-level ref isn't very informative,
+		 * the user won't be told *what* is a directory, so
+		 * let's not use strerror() below.
+		 */
+		int ignore_errno;
 		/* Expand dirname to the new prefix, not including the trailing slash: */
 		strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);
 
@@ -2238,7 +2262,8 @@ int refs_verify_refname_available(struct ref_store *refs,
 		if (skip && string_list_has_string(skip, dirname.buf))
 			continue;
 
-		if (!refs_read_raw_ref(refs, dirname.buf, &oid, &referent, &type)) {
+		if (!refs_read_raw_ref(refs, dirname.buf, &oid, &referent,
+				       &type, &ignore_errno)) {
 			strbuf_addf(err, _("'%s' exists; cannot create '%s'"),
 				    dirname.buf, refname);
 			goto cleanup;
diff --git a/refs/files-backend.c b/refs/files-backend.c
index c4b5b70c53..3eef442c24 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -381,10 +381,11 @@ static int files_read_raw_ref(struct ref_store *ref_store, const char *refname,
 		goto out;
 
 	if (lstat(path, &st) < 0) {
+		int ignore_errno;
 		if (errno != ENOENT)
 			goto out;
-		if (refs_read_raw_ref(refs->packed_ref_store, refname,
-				      oid, referent, type)) {
+		if (refs_read_raw_ref(refs->packed_ref_store, refname, oid,
+				      referent, type, &ignore_errno)) {
 			errno = ENOENT;
 			goto out;
 		}
@@ -418,13 +419,14 @@ static int files_read_raw_ref(struct ref_store *ref_store, const char *refname,
 
 	/* Is it a directory? */
 	if (S_ISDIR(st.st_mode)) {
+		int ignore_errno;
 		/*
 		 * Even though there is a directory where the loose
 		 * ref is supposed to be, there could still be a
 		 * packed ref:
 		 */
-		if (refs_read_raw_ref(refs->packed_ref_store, refname,
-				      oid, referent, type)) {
+		if (refs_read_raw_ref(refs->packed_ref_store, refname, oid,
+				      referent, type, &ignore_errno)) {
 			errno = EISDIR;
 			goto out;
 		}
diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index a457f18e93..928e5d2a99 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -1347,6 +1347,7 @@ int is_packed_transaction_needed(struct ref_store *ref_store,
 	ret = 0;
 	for (i = 0; i < transaction->nr; i++) {
 		struct ref_update *update = transaction->updates[i];
+		int failure_errno;
 		unsigned int type;
 		struct object_id oid;
 
@@ -1357,9 +1358,9 @@ int is_packed_transaction_needed(struct ref_store *ref_store,
 			 */
 			continue;
 
-		if (!refs_read_raw_ref(ref_store, update->refname,
-				       &oid, &referent, &type) ||
-		    errno != ENOENT) {
+		if (!refs_read_raw_ref(ref_store, update->refname, &oid,
+				       &referent, &type, &failure_errno) ||
+		    failure_errno != ENOENT) {
 			/*
 			 * We have to actually delete that reference
 			 * -> this transaction is needed.
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 79dfb3af48..54f57c6a2d 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -149,9 +149,9 @@ struct ref_update {
 	const char refname[FLEX_ARRAY];
 };
 
-int refs_read_raw_ref(struct ref_store *ref_store,
-		      const char *refname, struct object_id *oid,
-		      struct strbuf *referent, unsigned int *type);
+int refs_read_raw_ref(struct ref_store *ref_store, const char *refname,
+		      struct object_id *oid, struct strbuf *referent,
+		      unsigned int *type, int *failure_errno);
 
 /*
  * Write an error to `err` and return a nonzero value iff the same
-- 
2.32.0.851.g0fc62a9785

