virprocess: Passthru error from virProcessRunInForkHelper

When running a function in a forked child, so far the only thing
we could report is exit status of the child and the error
message. However, it may be beneficial to the caller to know the
actual error that happened in the child.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NPavel Mores <pmores@redhat.com>

build-aux/syntax-check.mk

@@ -1987,7 +1987,7 @@ exclude_file_name_regexp--sc_flags_usage = \
 exclude_file_name_regexp--sc_libvirt_unmarked_diagnostics = \
   ^(src/rpc/gendispatch\.pl$$|tests/)
 
-exclude_file_name_regexp--sc_po_check = ^(docs/|src/rpc/gendispatch\.pl$$)
+exclude_file_name_regexp--sc_po_check = ^(docs/|src/rpc/gendispatch\.pl$$|tests/commandtest.c$$)
 
 exclude_file_name_regexp--sc_prohibit_VIR_ERR_NO_MEMORY = \
   ^(build-aux/syntax-check\.mk|include/libvirt/virterror\.h|src/remote/remote_daemon_dispatch\.c|src/util/virerror\.c|docs/internals/oomtesting\.html\.in)$$

src/util/virprocess.c

@@ -1126,6 +1126,23 @@ virProcessRunInMountNamespace(pid_t pid G_GNUC_UNUSED,
 
 
 #ifndef WIN32
+typedef struct {
+    int code;
+    int domain;
+    char message[VIR_ERROR_MAX_LENGTH];
+    virErrorLevel level;
+    char str1[VIR_ERROR_MAX_LENGTH];
+    char str2[VIR_ERROR_MAX_LENGTH];
+    char str3[VIR_ERROR_MAX_LENGTH];
+    int int1;
+    int int2;
+} errorData;
+
+typedef union {
+    errorData data;
+    char bindata[sizeof(errorData)];
+} errorDataBin;
+
 static int
 virProcessRunInForkHelper(int errfd,
                           pid_t ppid,
@@ -1134,9 +1151,24 @@ virProcessRunInForkHelper(int errfd,
 {
     if (cb(ppid, opaque) < 0) {
         virErrorPtr err = virGetLastError();
+
         if (err) {
-            size_t len = strlen(err->message) + 1;
-            ignore_value(safewrite(errfd, err->message, len));
+            g_autofree errorDataBin *bin = g_new0(errorDataBin, 1);
+
+            bin->data.code = err->code;
+            bin->data.domain = err->domain;
+            ignore_value(virStrcpy(bin->data.message, err->message, sizeof(bin->data.message)));
+            bin->data.level = err->level;
+            if (err->str1)
+                ignore_value(virStrcpy(bin->data.str1, err->str1, sizeof(bin->data.str1)));
+            if (err->str2)
+                ignore_value(virStrcpy(bin->data.str2, err->str2, sizeof(bin->data.str2)));
+            if (err->str3)
+                ignore_value(virStrcpy(bin->data.str3, err->str3, sizeof(bin->data.str3)));
+            bin->data.int1 = err->int1;
+            bin->data.int2 = err->int2;
+
+            ignore_value(safewrite(errfd, bin->bindata, sizeof(*bin)));
         }
 
         return -1;
@@ -1188,16 +1220,38 @@ virProcessRunInFork(virProcessForkCallback cb,
     } else {
         int status;
         g_autofree char *buf = NULL;
+        g_autofree errorDataBin *bin = NULL;
+        int nread;
 
         VIR_FORCE_CLOSE(errfd[1]);
-        ignore_value(virFileReadHeaderFD(errfd[0], 1024, &buf));
+        nread = virFileReadHeaderFD(errfd[0], sizeof(*bin), &buf);
         ret = virProcessWait(child, &status, false);
         if (ret == 0) {
             ret = status == EXIT_CANCELED ? -1 : status;
             if (ret) {
-                virReportError(VIR_ERR_INTERNAL_ERROR,
-                               _("child reported (status=%d): %s"),
-                               status, NULLSTR(buf));
+                if (nread == sizeof(*bin)) {
+                    bin = g_new0(errorDataBin, 1);
+                    memcpy(bin->bindata, buf, sizeof(*bin));
+
+                    virReportError(VIR_ERR_INTERNAL_ERROR,
+                                   _("child reported (status=%d): %s"),
+                                   status, NULLSTR(bin->data.message));
+
+                    virRaiseErrorFull(__FILE__, __FUNCTION__, __LINE__,
+                                      bin->data.domain,
+                                      bin->data.code,
+                                      bin->data.level,
+                                      bin->data.str1,
+                                      bin->data.str2,
+                                      bin->data.str3,
+                                      bin->data.int1,
+                                      bin->data.int2,
+                                      "%s", bin->data.message);
+                } else {
+                    virReportError(VIR_ERR_INTERNAL_ERROR,
+                                   _("child didn't write error (status=%d)"),
+                                   status);
+                }
             }
         }
     }

tests/commandtest.c

@@ -1257,6 +1257,48 @@ static int test27(const void *unused G_GNUC_UNUSED)
 }
 
 
+static int
+test28Callback(pid_t pid G_GNUC_UNUSED,
+               void *opaque G_GNUC_UNUSED)
+{
+    virReportSystemError(ENODATA, "%s", "some error message");
+    return -1;
+}
+
+
+static int
+test28(const void *unused G_GNUC_UNUSED)
+{
+    /* Not strictly a virCommand test, but this is the easiest place
+     * to test this lower-level interface. */
+    virErrorPtr err;
+
+    if (virProcessRunInFork(test28Callback, NULL) != -1) {
+        fprintf(stderr, "virProcessRunInFork did not fail\n");
+        return -1;
+    }
+
+    if (!(err = virGetLastError())) {
+        fprintf(stderr, "Expected error but got nothing\n");
+        return -1;
+    }
+
+    if (!(err->code == VIR_ERR_SYSTEM_ERROR &&
+          err->domain == 0 &&
+          STREQ(err->message, "some error message: No data available") &&
+          err->level == VIR_ERR_ERROR &&
+          STREQ(err->str1, "%s") &&
+          STREQ(err->str2, "some error message: No data available") &&
+          err->int1 == ENODATA &&
+          err->int2 == -1)) {
+        fprintf(stderr, "Unexpected error object\n");
+        return -1;
+    }
+
+    return 0;
+}
+
+
 static int
 mymain(void)
 {
@@ -1354,6 +1396,7 @@ mymain(void)
     DO_TEST(test25);
     DO_TEST(test26);
     DO_TEST(test27);
+    DO_TEST(test28);
 
     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }