[Qemu-devel] [PULL 0/3] Error reporting patches for 2016-02-09

[Qemu-devel] [PULL 0/3] Error reporting patches for 2016-02-09

[Markus Armbruster]

The following changes since commit e4a096b1cd4350eeca5dcdc391ab333d2083d7fd:

  ui/cocoa.m: Include qemu/osdep.h (2016-02-08 13:14:40 +0000)

are available in the git repository at:

  git://repo.or.cz/qemu/armbru.git tags/pull-error-2016-02-09

for you to fetch changes up to d76a3bf5c46d9e981faf09e6194c795ee54e5ae4:

  HACKING: Add a section on error handling and reporting (2016-02-09 13:19:49 +0100)

----------------------------------------------------------------
Error reporting patches for 2016-02-09

----------------------------------------------------------------
Markus Armbruster (3):
      Use error_fatal to simplify obvious fatal errors (again)
      error: Improve documentation some more
      HACKING: Add a section on error handling and reporting

 HACKING              | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 hw/arm/imx25_pdk.c   |  7 +------
 hw/arm/kzm.c         |  7 +------
 hw/arm/netduino2.c   |  7 +------
 hw/arm/xlnx-ep108.c  |  7 +------
 include/qapi/error.h | 15 ++++++++++----
 vl.c                 |  7 +------
 7 files changed, 71 insertions(+), 34 deletions(-)

-- 
2.4.3

[Qemu-devel] [PULL 1/3] Use error_fatal to simplify obvious fatal errors (again)

[Markus Armbruster]

Done with the Coccinelle semantic patch from commit 007b065, plus
manual clean up of dead variables.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1452783732-6581-1-git-send-email-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 hw/arm/imx25_pdk.c  | 7 +------
 hw/arm/kzm.c        | 7 +------
 hw/arm/netduino2.c  | 7 +------
 hw/arm/xlnx-ep108.c | 7 +------
 vl.c                | 7 +------
 5 files changed, 5 insertions(+), 30 deletions(-)

diff --git a/hw/arm/imx25_pdk.c b/hw/arm/imx25_pdk.c
index b167e19..e3cffd1 100644
--- a/hw/arm/imx25_pdk.c
+++ b/hw/arm/imx25_pdk.c
@@ -65,7 +65,6 @@ static struct arm_boot_info imx25_pdk_binfo;
 static void imx25_pdk_init(MachineState *machine)
 {
     IMX25PDK *s = g_new0(IMX25PDK, 1);
-    Error *err = NULL;
     unsigned int ram_size;
     unsigned int alias_offset;
     int i;
@@ -74,11 +73,7 @@ static void imx25_pdk_init(MachineState *machine)
     object_property_add_child(OBJECT(machine), "soc", OBJECT(&s->soc),
                               &error_abort);
 
-    object_property_set_bool(OBJECT(&s->soc), true, "realized", &err);
-    if (err != NULL) {
-        error_report_err(err);
-        exit(1);
-    }
+    object_property_set_bool(OBJECT(&s->soc), true, "realized", &error_fatal);
 
     /* We need to initialize our memory */
     if (machine->ram_size > (FSL_IMX25_SDRAM0_SIZE + FSL_IMX25_SDRAM1_SIZE)) {
diff --git a/hw/arm/kzm.c b/hw/arm/kzm.c
index 55fb360..2eeb9d8 100644
--- a/hw/arm/kzm.c
+++ b/hw/arm/kzm.c
@@ -64,7 +64,6 @@ static struct arm_boot_info kzm_binfo = {
 static void kzm_init(MachineState *machine)
 {
     IMX31KZM *s = g_new0(IMX31KZM, 1);
-    Error *err = NULL;
     unsigned int ram_size;
     unsigned int alias_offset;
     unsigned int i;
@@ -73,11 +72,7 @@ static void kzm_init(MachineState *machine)
     object_property_add_child(OBJECT(machine), "soc", OBJECT(&s->soc),
                               &error_abort);
 
-    object_property_set_bool(OBJECT(&s->soc), true, "realized", &err);
-    if (err != NULL) {
-        error_report_err(err);
-        exit(1);
-    }
+    object_property_set_bool(OBJECT(&s->soc), true, "realized", &error_fatal);
 
     /* Check the amount of memory is compatible with the SOC */
     if (machine->ram_size > (FSL_IMX31_SDRAM0_SIZE + FSL_IMX31_SDRAM1_SIZE)) {
diff --git a/hw/arm/netduino2.c b/hw/arm/netduino2.c
index 86065d3..49da6e3 100644
--- a/hw/arm/netduino2.c
+++ b/hw/arm/netduino2.c
@@ -30,18 +30,13 @@
 static void netduino2_init(MachineState *machine)
 {
     DeviceState *dev;
-    Error *err = NULL;
 
     dev = qdev_create(NULL, TYPE_STM32F205_SOC);
     if (machine->kernel_filename) {
         qdev_prop_set_string(dev, "kernel-filename", machine->kernel_filename);
     }
     qdev_prop_set_string(dev, "cpu-model", "cortex-m3");
-    object_property_set_bool(OBJECT(dev), true, "realized", &err);
-    if (err != NULL) {
-        error_report_err(err);
-        exit(1);
-    }
+    object_property_set_bool(OBJECT(dev), true, "realized", &error_fatal);
 }
 
 static void netduino2_machine_init(MachineClass *mc)
diff --git a/hw/arm/xlnx-ep108.c b/hw/arm/xlnx-ep108.c
index 2cd69b5..0de132a 100644
--- a/hw/arm/xlnx-ep108.c
+++ b/hw/arm/xlnx-ep108.c
@@ -32,7 +32,6 @@ static void xlnx_ep108_init(MachineState *machine)
 {
     XlnxEP108 *s = g_new0(XlnxEP108, 1);
     int i;
-    Error *err = NULL;
     uint64_t ram_size = machine->ram_size;
 
     /* Create the memory region to pass to the SoC */
@@ -58,11 +57,7 @@ static void xlnx_ep108_init(MachineState *machine)
     object_property_set_link(OBJECT(&s->soc), OBJECT(&s->ddr_ram),
                          "ddr-ram", &error_abort);
 
-    object_property_set_bool(OBJECT(&s->soc), true, "realized", &err);
-    if (err) {
-        error_report_err(err);
-        exit(1);
-    }
+    object_property_set_bool(OBJECT(&s->soc), true, "realized", &error_fatal);
 
     for (i = 0; i < XLNX_ZYNQMP_NUM_SPIS; i++) {
         SSIBus *spi_bus;
diff --git a/vl.c b/vl.c
index c581e39..a5502ed 100644
--- a/vl.c
+++ b/vl.c
@@ -4555,12 +4555,7 @@ int main(int argc, char **argv, char **envp)
     net_check_clients();
 
     if (boot_once) {
-        Error *local_err = NULL;
-        qemu_boot_set(boot_once, &local_err);
-        if (local_err) {
-            error_report_err(local_err);
-            exit(1);
-        }
+        qemu_boot_set(boot_once, &error_fatal);
         qemu_register_reset(restore_boot_order, g_strdup(boot_order));
     }
 
-- 
2.4.3

[Qemu-devel] [PULL 2/3] error: Improve documentation some more

[Markus Armbruster]

Don't claim error_report_err() always reports to stderr.  It actually
reports to the current monitor when we have one.

Clarify intended use of error_abort and error_fatal.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1454522628-28294-2-git-send-email-armbru@redhat.com>
Reviewed-by: Lluís Vilanova <vilanova@ac.upc.edu>
---
 include/qapi/error.h | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/qapi/error.h b/include/qapi/error.h
index 45d6c72..e64fe54 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -27,11 +27,11 @@
  *     error_setg(&err, "invalid quark\n"
  *                "Valid quarks are up, down, strange, charm, top, bottom.");
  *
- * Report an error to stderr:
+ * Report an error to the current monitor if we have one, else stderr:
  *     error_report_err(err);
  * This frees the error object.
  *
- * Report an error to stderr with additional text prepended:
+ * Likewise, but with additional text prepended:
  *     error_reportf_err(err, "Could not frobnicate '%s': ", name);
  *
  * Report an error somewhere else:
@@ -162,6 +162,9 @@ ErrorClass error_get_class(const Error *err);
  * human-readable error message is made from printf-style @fmt, ...
  * The resulting message should be a single phrase, with no newline or
  * trailing punctuation.
+ * Please don't error_setg(&error_fatal, ...), use error_report() and
+ * exit(), because that's more obvious.
+ * Likewise, don't error_setg(&error_abort, ...), use assert().
  */
 #define error_setg(errp, fmt, ...)                              \
     error_setg_internal((errp), __FILE__, __LINE__, __func__,   \
@@ -213,6 +216,8 @@ void error_setg_win32_internal(Error **errp,
  * the error object.
  * Else, move the error object from @local_err to *@dst_errp.
  * On return, @local_err is invalid.
+ * Please don't error_propagate(&error_fatal, ...), use
+ * error_report_err() and exit(), because that's more obvious.
  */
 void error_propagate(Error **dst_errp, Error *local_err);
 
@@ -291,12 +296,14 @@ void error_set_internal(Error **errp,
     GCC_FMT_ATTR(6, 7);
 
 /*
- * Pass to error_setg() & friends to abort() on error.
+ * Special error destination to abort on error.
+ * See error_setg() and error_propagate() for details.
  */
 extern Error *error_abort;
 
 /*
- * Pass to error_setg() & friends to exit(1) on error.
+ * Special error destination to exit(1) on error.
+ * See error_setg() and error_propagate() for details.
  */
 extern Error *error_fatal;
 
-- 
2.4.3

[Qemu-devel] [PULL 3/3] HACKING: Add a section on error handling and reporting

[Markus Armbruster]

Inspired by an RFC PATCH from Lluís Vilanova.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1454522628-28294-3-git-send-email-armbru@redhat.com>
Reviewed-by: Lluís Vilanova <vilanova@ac.upc.edu>
---
 HACKING | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/HACKING b/HACKING
index 12fbc8a..058aa8f 100644
--- a/HACKING
+++ b/HACKING
@@ -157,3 +157,58 @@ painful. These are:
  * you may assume that integers are 2s complement representation
  * you may assume that right shift of a signed integer duplicates
    the sign bit (ie it is an arithmetic shift, not a logical shift)
+
+7. Error handling and reporting
+
+7.1 Reporting errors to the human user
+
+Do not use printf(), fprintf() or monitor_printf().  Instead, use
+error_report() or error_vreport() from error-report.h.  This ensures the
+error is reported in the right place (current monitor or stderr), and in
+a uniform format.
+
+Use error_printf() & friends to print additional information.
+
+error_report() prints the current location.  In certain common cases
+like command line parsing, the current location is tracked
+automatically.  To manipulate it manually, use the loc_*() from
+error-report.h.
+
+7.2 Propagating errors
+
+An error can't always be reported to the user right where it's detected,
+but often needs to be propagated up the call chain to a place that can
+handle it.  This can be done in various ways.
+
+The most flexible one is Error objects.  See error.h for usage
+information.
+
+Use the simplest suitable method to communicate success / failure to
+callers.  Stick to common methods: non-negative on success / -1 on
+error, non-negative / -errno, non-null / null, or Error objects.
+
+Example: when a function returns a non-null pointer on success, and it
+can fail only in one way (as far as the caller is concerned), returning
+null on failure is just fine, and certainly simpler and a lot easier on
+the eyes than propagating an Error object through an Error ** parameter.
+
+Example: when a function's callers need to report details on failure
+only the function really knows, use Error **, and set suitable errors.
+
+Do not report an error to the user when you're also returning an error
+for somebody else to handle.  Leave the reporting to the place that
+consumes the error returned.
+
+7.3 Handling errors
+
+Calling exit() is fine when handling configuration errors during
+startup.  It's problematic during normal operation.  In particular,
+monitor commands should never exit().
+
+Do not call exit() or abort() to handle an error that can be triggered
+by the guest (e.g., some unimplemented corner case in guest code
+translation or device emulation).  Guests should not be able to
+terminate QEMU.
+
+Note that &error_fatal is just another way to exit(1), and &error_abort
+is just another way to abort().
-- 
2.4.3

Re: [Qemu-devel] [PULL 0/3] Error reporting patches for 2016-02-09

[Peter Maydell]

On 9 February 2016 at 13:25, Markus Armbruster <armbru@redhat.com> wrote:
> The following changes since commit e4a096b1cd4350eeca5dcdc391ab333d2083d7fd:
>
>   ui/cocoa.m: Include qemu/osdep.h (2016-02-08 13:14:40 +0000)
>
> are available in the git repository at:
>
>   git://repo.or.cz/qemu/armbru.git tags/pull-error-2016-02-09
>
> for you to fetch changes up to d76a3bf5c46d9e981faf09e6194c795ee54e5ae4:
>
>   HACKING: Add a section on error handling and reporting (2016-02-09 13:19:49 +0100)
>
> ----------------------------------------------------------------
> Error reporting patches for 2016-02-09
>
> ----------------------------------------------------------------
> Markus Armbruster (3):
>       Use error_fatal to simplify obvious fatal errors (again)
>       error: Improve documentation some more
>       HACKING: Add a section on error handling and reporting
>

Applied, thanks.

-- PMM