daemon error handling: Define a new function reply_with_perror_errno.

This allows you to save the errno from a previous call and
pass it to reply_with_perror.

For example, original code:

  r = some_system_call ();
  err = errno;
  do_cleanup ();
  errno = err;
  if (r == -1) {
    reply_with_perror ("failed");
    return -1;
  }

can in future be changed to:

  r = some_system_call ();
  err = errno;
  do_cleanup ();
  if (r == -1) {
    reply_with_perror_errno (err, "failed");
    return -1;
  }

2 files changed, 5 insertions, 5 deletions

diff --git a/daemon/daemon.h b/daemon/daemon.h
index 6ce46b9c..88d03065 100644
--- a/daemon/daemon.h
+++ b/daemon/daemon.h
@@ -119,8 +119,9 @@ extern void main_loop (int sock) __attribute__((noreturn));
 /* ordinary daemon functions use these to indicate errors */
 extern void reply_with_error (const char *fs, ...)
   __attribute__((format (printf,1,2)));
-extern void reply_with_perror (const char *fs, ...)
-  __attribute__((format (printf,1,2)));
+extern void reply_with_perror_errno (int err, const char *fs, ...)
+  __attribute__((format (printf,2,3)));
+#define reply_with_perror(...) reply_with_perror_errno(errno, __VA_ARGS__)
 
 /* daemon functions that receive files (FileIn) should call
  * receive_file for each FileIn parameter.
@@ -130,7 +131,7 @@ extern int receive_file (receive_cb cb, void *opaque);
 
 /* daemon functions that receive files (FileIn) can call this
  * to cancel incoming transfers (eg. if there is a local error),
- * but they MUST then call reply_with_error or reply_with_perror.
+ * but they MUST then call reply_with_*.
  */
 extern void cancel_receive (void);
 
diff --git a/daemon/proto.c b/daemon/proto.c
index e3ff9e9d..1ad9d111 100644
--- a/daemon/proto.c
+++ b/daemon/proto.c
@@ -195,12 +195,11 @@ reply_with_error (const char *fs, ...)
 }
 
 void
-reply_with_perror (const char *fs, ...)
+reply_with_perror_errno (int err, const char *fs, ...)
 {
   char buf1[GUESTFS_ERROR_LEN];
   char buf2[GUESTFS_ERROR_LEN];
   va_list args;
-  int err = errno;
 
   va_start (args, fs);
   vsnprintf (buf1, sizeof buf1, fs, args);