[libvirt] [PATCH] qemu: Report errors from iohelper

[Michal Privoznik]

Currently, we use iohelper when saving/restoring a domain.
However, if there's some kind of error (like I/O) it is not
propagated to libvirt. Since it is not qemu who is doing
the actual write() it will not get error. The iohelper does.
Therefore we should check for iohelper errors as it makes
libvirt more user friendly.
---
 src/libvirt_private.syms |    1 +
 src/qemu/qemu_driver.c   |    7 ++++-
 src/util/virfile.c       |   47 ++++++++++++++++++++++++++++++++++++++++++++++
 src/util/virfile.h       |    2 +
 4 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 60f9c7f..26eb7b1 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1332,6 +1332,7 @@ virDomainListSnapshots;
 virFileLoopDeviceAssociate;
 virFileClose;
 virFileDirectFdFlag;
+virFileWrapperFdCatchError;
 virFileWrapperFdClose;
 virFileWrapperFdFree;
 virFileWrapperFdNew;
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 8af316f..c8e97cf 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -2945,6 +2945,7 @@ endjob:
                 if (rc < 0)
                     VIR_WARN("Unable to resume guest CPUs after save failure");
             }
+            virFileWrapperFdCatchError(wrapperFd);
         }
         if (qemuDomainObjEndAsyncJob(driver, vm) == 0)
             vm = NULL;
@@ -3282,9 +3283,11 @@ doCoreDump(struct qemud_driver *driver,
 
 cleanup:
     VIR_FORCE_CLOSE(fd);
-    virFileWrapperFdFree(wrapperFd);
-    if (ret != 0)
+    if (ret != 0) {
+        virFileWrapperFdCatchError(wrapperFd);
         unlink(path);
+    }
+    virFileWrapperFdFree(wrapperFd);
     return ret;
 }
 
diff --git a/src/util/virfile.c b/src/util/virfile.c
index 5b00ead..4d7538e 100644
--- a/src/util/virfile.c
+++ b/src/util/virfile.c
@@ -135,6 +135,7 @@ virFileDirectFdFlag(void)
  * read-write is not supported, just a single direction.  */
 struct _virFileWrapperFd {
     virCommandPtr cmd; /* Child iohelper process to do the I/O.  */
+    int err_fd; /* FD to read stderr of @cmd */
 };
 
 #ifndef WIN32
@@ -229,6 +230,14 @@ virFileWrapperFdNew(int *fd, const char *name, unsigned int flags)
         virCommandAddArg(ret->cmd, "0");
     }
 
+    /* In order to catch iohelper stderr, we must:
+     * - pass a FD to virCommand (-1 to auto-allocate one)
+     * - change iohelper's env so virLog functions print to stderr
+     */
+    ret->err_fd = -1;
+    virCommandSetErrorFD(ret->cmd, &ret->err_fd);
+    virCommandAddEnvPair(ret->cmd, "LIBVIRT_LOG_OUTPUTS", "1:stderr");
+
     if (virCommandRunAsync(ret->cmd, NULL) < 0)
         goto error;
 
@@ -280,6 +289,42 @@ virFileWrapperFdClose(virFileWrapperFdPtr wfd)
     return virCommandWait(wfd->cmd, NULL);
 }
 
+
+/**
+ * virFileWrapperFdCatchError:
+ * @wfd: fd wrapper, or NULL
+ *
+ * Read the stderr of iohelper and VIR_WARN() about it.
+ */
+void
+virFileWrapperFdCatchError(virFileWrapperFdPtr wfd)
+{
+    char *err = NULL;
+    char ebuf[1024];
+    size_t nread = 0;
+    size_t err_size = 0;
+
+    if (!wfd)
+        return;
+
+    while ((nread = saferead(wfd->err_fd, ebuf, sizeof(ebuf)))) {
+        if (VIR_REALLOC_N(err, err_size + nread + 1) < 0) {
+            virReportOOMError();
+            goto cleanup;
+        }
+        memcpy(err + err_size, ebuf, nread);
+        err_size += nread;
+        err[err_size] = '\0';
+    }
+
+    if (err)
+        VIR_WARN("iohelper reports: %s", err);
+
+cleanup:
+    VIR_FREE(err);
+}
+
+
 /**
  * virFileWrapperFdFree:
  * @wfd: fd wrapper, or NULL
@@ -295,6 +340,8 @@ virFileWrapperFdFree(virFileWrapperFdPtr wfd)
     if (!wfd)
         return;
 
+    VIR_FORCE_CLOSE(wfd->err_fd);
+
     virCommandFree(wfd->cmd);
     VIR_FREE(wfd);
 }
diff --git a/src/util/virfile.h b/src/util/virfile.h
index c885b73..80daf86 100644
--- a/src/util/virfile.h
+++ b/src/util/virfile.h
@@ -90,6 +90,8 @@ int virFileWrapperFdClose(virFileWrapperFdPtr dfd);
 
 void virFileWrapperFdFree(virFileWrapperFdPtr dfd);
 
+void virFileWrapperFdCatchError(virFileWrapperFdPtr dfd);
+
 int virFileLock(int fd, bool shared, off_t start, off_t len);
 int virFileUnlock(int fd, off_t start, off_t len);
 
-- 
1.7.8.6