[Xen-changelog] [xen staging] libxl: Enhance libxl__sendmsg_fds to deal with EINTR and EWOULDBLOCK

[patchbot@xxxxxxx]

commit 394dd1d2d49afe31432985c6c517a0a80b9c20fd
Author:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
AuthorDate: Wed Oct 31 16:31:49 2018 +0000
Commit:     Wei Liu <wei.liu2@xxxxxxxxxx>
CommitDate: Fri Jan 11 14:57:25 2019 +0000

    libxl: Enhance libxl__sendmsg_fds to deal with EINTR and EWOULDBLOCK
    
    This patch change the behavior of libxl__sendmsg_fds to retry sendmsg on
    EINTR error and return an error on short writes.
    
    This patch allow a caller of libxl__sendmsg_fds to deal with EWOULDBLOCK
    and short writes. The function now requires to send only 1 byte of data
    so that when dealing with non-blocking fds a EWOULDBLOCK error would
    mean that the fds haven't been sent yet. Current caller already send
    only 1 byte.
    
    Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
    [ wei: fix build ]
    Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/libxl/libxl_internal.h |  5 ++++-
 tools/libxl/libxl_utils.c    | 25 ++++++++++++++++++++-----
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 67f3f6ac76..aa9059ffec 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1876,7 +1876,10 @@ _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 */
+/* `datalen` should be 1 byte
+ * When dealing with a non-blocking fd, it returns
+ *   ERROR_NOT_READY on EWOULDBLOCK
+ * logs on other failures. */
 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..29a7dde59f 100644
--- a/tools/libxl/libxl_utils.c
+++ b/tools/libxl/libxl_utils.c
@@ -1070,6 +1070,8 @@ int libxl__sendmsg_fds(libxl__gc *gc, int carrier,
     struct iovec iov;
     int r;
 
+    assert(datalen == 1);
+
     iov.iov_base = (void*)data;
     iov.iov_len  = datalen;
 
@@ -1088,11 +1090,24 @@ 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) {
+                return ERROR_NOT_READY;
+            }
+            LOGE(ERROR, "failed to send fd-carrying message (%s)", what);
+            return ERROR_FAIL;
+        }
+        if (r != datalen) {
+            LOG(ERROR, "sendmsg have written %d instead of %zu",
+                r, datalen);
+            return ERROR_FAIL;
+        }
+        break;
+    };
 
     return 0;
 }
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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