[PATCH v4 01/17] tools/xenstore: let talloc_free() preserve errno

From: Juergen Gross <jgross@suse.com>
To: xen-devel@lists.xenproject.org
Cc: Juergen Gross <jgross@suse.com>, Wei Liu <wl@xen.org>,
	Julien Grall <julien@xen.org>,
	Anthony PERARD <anthony.perard@citrix.com>,
	Julien Grall <jgrall@amazon.com>
Subject: [PATCH v4 01/17] tools/xenstore: let talloc_free() preserve errno
Date: Wed, 18 Jan 2023 10:50:00 +0100	[thread overview]
Message-ID: <20230118095016.13091-2-jgross@suse.com> (raw)
In-Reply-To: <20230118095016.13091-1-jgross@suse.com>

Today talloc_free() is not guaranteed to preserve errno, especially in
case a custom destructor is being used.

So preserve errno in talloc_free().

This allows to remove some errno saving outside of talloc.c.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>
---
V2:
- drop wrapper (Julien Grall)
---
 tools/xenstore/talloc.c         | 21 +++++++++++++--------
 tools/xenstore/xenstored_core.c |  2 --
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/tools/xenstore/talloc.c b/tools/xenstore/talloc.c
index d7edcf3a93..23c3a23b19 100644
--- a/tools/xenstore/talloc.c
+++ b/tools/xenstore/talloc.c
@@ -541,38 +541,39 @@ static void talloc_free_children(void *ptr)
 */
 int talloc_free(void *ptr)
 {
+	int saved_errno = errno;
 	struct talloc_chunk *tc;
 
 	if (ptr == NULL) {
-		return -1;
+		goto err;
 	}
 
 	tc = talloc_chunk_from_ptr(ptr);
 
 	if (tc->null_refs) {
 		tc->null_refs--;
-		return -1;
+		goto err;
 	}
 
 	if (tc->refs) {
 		talloc_reference_destructor(tc->refs);
-		return -1;
+		goto err;
 	}
 
 	if (tc->flags & TALLOC_FLAG_LOOP) {
 		/* we have a free loop - stop looping */
-		return 0;
+		goto success;
 	}
 
 	if (tc->destructor) {
 		talloc_destructor_t d = tc->destructor;
 		if (d == (talloc_destructor_t)-1) {
-			return -1;
+			goto err;
 		}
 		tc->destructor = (talloc_destructor_t)-1;
 		if (d(ptr) == -1) {
 			tc->destructor = d;
-			return -1;
+			goto err;
 		}
 		tc->destructor = NULL;
 	}
@@ -594,10 +595,14 @@ int talloc_free(void *ptr)
 	tc->flags |= TALLOC_FLAG_FREE;
 
 	free(tc);
+ success:
+	errno = saved_errno;
 	return 0;
-}
-
 
+ err:
+	errno = saved_errno;
+	return -1;
+}
 
 /*
   A talloc version of realloc. The context argument is only used if
diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 78a3edaa4e..1650821922 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -771,9 +771,7 @@ struct node *read_node(struct connection *conn, const void *ctx,
 	return node;
 
  error:
-	err = errno;
 	talloc_free(node);
-	errno = err;
 	return NULL;
 }
 
-- 
2.35.3


