libvirt_iohelper is used internally by the virFileWrapperFd APIs;
more specifically, in the QEMU driver we have the doCoreDump() and
qemuDomainSaveMemory() helper functions as users, and those in turn
end up being called by the implementation of several driver APIs.

By calling virReportError() if libvirt_iohelper has failed, we
overwrite whatever generic error message QEMU might have raised
with the more useful one generated by the helper program.

After this commit, the user will be able to see the error directly
instead of having to dig in the journal or libvirtd log.

https://bugzilla.redhat.com/show_bug.cgi?id=1578741

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
---
 src/util/virfile.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/util/virfile.c b/src/util/virfile.c
index d35206b0dd..31030c7b34 100644
--- a/src/util/virfile.c
+++ b/src/util/virfile.c
@@ -337,8 +337,14 @@ virFileWrapperFdClose(virFileWrapperFdPtr wfd)
 
     ret = virCommandWait(wfd->cmd, NULL);
 
-    if (wfd->err_msg && *wfd->err_msg)
-        VIR_WARN("iohelper reports: %s", wfd->err_msg);
+    /* If the command used to process I/O has failed and produced some
+     * messages on stderr, it's fair to assume those will be more
+     * relevant to the user than whatever eg. QEMU can figure out on its
+     * own having no knowledge of the fact a command is handling its I/O
+     * in the first place, so it's okay if we end up discarding an
+     * existing error here */
+    if (ret < 0 && wfd->err_msg && *wfd->err_msg)
+        virReportError(VIR_ERR_OPERATION_FAILED, "%s", wfd->err_msg);
 
     wfd->closed = true;
 
-- 
2.20.1

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