From 334ab902477a0e1db4d70a5c809eafe49ab1fc6e Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Wed, 24 Jul 2024 10:37:58 +0100
Subject: [PATCH] server: Introduce threadlocal_{set,get}_last_error

Plus a function to clear the last_error field.

(cherry picked from commit fa5055ae2b9f96af941d697de39198c96ee2580a)
---
 server/internal.h    |  3 +++
 server/threadlocal.c | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/server/internal.h b/server/internal.h
index 6549c87b..da19fb99 100644
--- a/server/internal.h
+++ b/server/internal.h
@@ -570,6 +570,9 @@ extern void threadlocal_set_instance_num (size_t instance_num);
 extern size_t threadlocal_get_instance_num (void);
 extern void threadlocal_set_errno (int err);
 extern int threadlocal_get_errno (void);
+extern void threadlocal_set_last_error (char *msg);
+extern void threadlocal_clear_last_error (void);
+extern const char *threadlocal_get_last_error (void);
 extern void *threadlocal_buffer (size_t size);
 extern void threadlocal_set_conn (struct connection *conn);
 extern struct connection *threadlocal_get_conn (void);
diff --git a/server/threadlocal.c b/server/threadlocal.c
index 9bb656bc..74a3c4e5 100644
--- a/server/threadlocal.c
+++ b/server/threadlocal.c
@@ -56,6 +56,7 @@ struct threadlocal {
   char *name;                   /* Can be NULL. */
   size_t instance_num;          /* Can be 0. */
   int err;
+  char *last_error;             /* Can be NULL. */
   void *buffer;                 /* Can be NULL. */
   size_t buffer_size;
   struct connection *conn;      /* Can be NULL. */
@@ -70,6 +71,7 @@ free_threadlocal (void *threadlocalv)
   struct threadlocal *threadlocal = threadlocalv;
 
   free (threadlocal->name);
+  free (threadlocal->last_error);
   free (threadlocal->buffer);
   free (threadlocal);
 }
@@ -176,6 +178,44 @@ threadlocal_get_errno (void)
   return threadlocal ? threadlocal->err : 0;
 }
 
+/* Set the last_error field.  The ownership of the 'msg' string is
+ * passed to the threadlocal and will be freed here.
+ */
+void
+threadlocal_set_last_error (char *msg)
+{
+  struct threadlocal *threadlocal = pthread_getspecific (threadlocal_key);
+
+  if (threadlocal) {
+    free (threadlocal->last_error);
+    threadlocal->last_error = msg;
+  }
+  else {
+    /* ... otherwise throw it away, it's informational. */
+    free (msg);
+  }
+}
+
+void
+threadlocal_clear_last_error (void)
+{
+  threadlocal_set_last_error (NULL);
+}
+
+/* Get the last_error field.  If successful, this returns a non-NULL
+ * string.  This is valid until something calls nbdkit_error() in the
+ * same thread, so it should be used quickly.  Returning NULL is not
+ * necessarily an error.  The last_error is informational and may not
+ * be available.
+ */
+const char *
+threadlocal_get_last_error (void)
+{
+  struct threadlocal *threadlocal = pthread_getspecific (threadlocal_key);
+
+  return threadlocal ? threadlocal->last_error : NULL;
+}
+
 /* Return the single pread/pwrite buffer for this thread.  The buffer
  * size is increased to ‘size’ bytes if required.
  *
-- 
2.43.0