[PATCH 01/11] libxl: Make logging functions preserve errno

[Ian Jackson <ian.jackson@eu.citrix.com>]

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>
---
 tools/libxl/libxl_internal.c |    5 ++++-
 tools/libxl/libxl_internal.h |    2 ++
 2 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
index f48e9eb..4dcdabe 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,
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 300c108..10e72e5 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -47,6 +47,7 @@
 #define XL_LOG_ERRNO(ctx, loglevel, _f, _a...)
 #define XL_LOG_ERRNOVAL(ctx, loglevel, errnoval, _f, _a...)
 #endif
+  /* all of these macros preserve errno (saving and restoring) */
 
 #define XL_LOG_DEBUG 3
 #define XL_LOG_INFO 2
@@ -56,6 +57,7 @@
 /* logging */
 void xl_logv(struct libxl_ctx *ctx, int errnoval, int loglevel, const char *file, int line, const char *func, char *fmt, va_list al);
 void xl_log(struct libxl_ctx *ctx, int errnoval, int loglevel, const char *file, int line, const char *func, char *fmt, ...);
+  /* these functions preserve errno (saving and restoring) */
 
 
 typedef enum {
-- 
1.5.6.5