libxl: Make logging functions preserve errno

This is needed by the following patches.  It makes it much more
convenient for libxl functions to return the errno value from the
failure, when they fail.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
index f48e9eb109..4dcdabe653 100644
--- a/tools/libxl/libxl_internal.c
+++ b/tools/libxl/libxl_internal.c
@@ -156,11 +156,13 @@ void xl_logv(struct libxl_ctx *ctx, int loglevel, int errnoval,
 {
     char *enomem = "[out of memory formatting log message]";
     char *s;
-    int rc;
+    int rc, esave;
 
     if (!ctx->log_callback)
         return;
 
+    esave = errno;
+    
     rc = vasprintf(&s, fmt, ap);
     if (rc<0) { s = enomem; goto x; }
 
@@ -180,6 +182,7 @@ void xl_logv(struct libxl_ctx *ctx, int loglevel, int errnoval,
     ctx->log_callback(ctx->log_userdata, loglevel, file, line, func, s);
     if (s != enomem)
         free(s);
+    errno = esave;
 }
 
 void xl_log(struct libxl_ctx *ctx, int loglevel, int errnoval,