[Xen-devel] [PATCH v6 01/11] libxl: Enhance libxl__sendmsg_fds to deal with EINTR and EWOULDBLOCK

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

This patch change the behavior of libxl__sendmsg_fds to retry sendmsg on
EINTR error.

This patch also allow a caller of libxl__sendmsg_fds to deal with
EWOULDBLOCK. It is best to only sent one byte when dealing with
non-blocking fds so a EWOULDBLOCK error would mean that the fds haven't
been sent yet.

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 tools/libxl/libxl_internal.h |  3 ++-
 tools/libxl/libxl_utils.c    | 19 ++++++++++++++-----
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index e498435e16..ae5960d869 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1864,7 +1864,8 @@ _hidden void libxl__qmp_cleanup(libxl__gc *gc, uint32_t 
domid);
 _hidden int libxl__qmp_initializations(libxl__gc *gc, uint32_t domid,
                                        const libxl_domain_config 
*guest_config);
 
-/* on failure, logs */
+/* returns ERROR_NOT_READY on EWOULDBLOCK
+ * or logs on failure. */
 int libxl__sendmsg_fds(libxl__gc *gc, int carrier,
                        const void *data, size_t datalen,
                        int nfds, const int fds[], const char *what);
diff --git a/tools/libxl/libxl_utils.c b/tools/libxl/libxl_utils.c
index 5854717b11..5d20fd57c5 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/libxl_utils.c
@@ -1088,11 +1088,20 @@ int libxl__sendmsg_fds(libxl__gc *gc, int carrier,
 
     msg.msg_controllen = cmsg->cmsg_len;
 
-    r = sendmsg(carrier, &msg, 0);
-    if (r < 0) {
-        LOGE(ERROR, "failed to send fd-carrying message (%s)", what);
-        return ERROR_FAIL;
-    }
+    while (1) {
+        r = sendmsg(carrier, &msg, 0);
+        if (r < 0) {
+            if (errno == EINTR)
+                continue;
+            if (errno == EWOULDBLOCK) {
+                assert(datalen == 1);
+                return ERROR_NOT_READY;
+            }
+            LOGE(ERROR, "failed to send fd-carrying message (%s)", what);
+            return ERROR_FAIL;
+        }
+        break;
+    };
 
     return 0;
 }
-- 
Anthony PERARD


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