[Qemu-devel] [PATCH 0/6] Convert to realize and improve error handling

[Qemu-devel] [PATCH 0/6] Convert to realize and improve error handling

[Mao Zhongyi]

This series mainly implements the conversions of ide, floppy and nvme
device to realize. Add some error handling messages and remove the local
variable local_err, use errp to propagate the error directly. Also
fix the unusual function name.

Cc: John Snow <jsnow@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>

Mao Zhongyi (6):
  hw/ide: Convert DeviceClass init to realize
  hw/block/fdc: Convert to realize
  hw/block/nvme: Convert to realize
  hw/block: Fix the return type
  hw/block: Use errp directly rather than local_err
  dev-storage: Fix the unusual function name

 hw/block/block.c                | 21 +++++----
 hw/block/dataplane/virtio-blk.c | 16 ++++---
 hw/block/dataplane/virtio-blk.h |  6 +--
 hw/block/fdc.c                  | 48 +++++++++------------
 hw/block/nvme.c                 | 24 +++++------
 hw/block/virtio-blk.c           | 17 +++-----
 hw/ide/core.c                   |  7 +--
 hw/ide/qdev.c                   | 94 +++++++++++++++++++----------------------
 hw/scsi/scsi-disk.c             | 13 ++----
 hw/usb/dev-storage.c            | 29 ++++++-------
 include/hw/block/block.h        | 10 ++---
 include/hw/ide/internal.h       |  5 ++-
 12 files changed, 135 insertions(+), 155 deletions(-)

-- 
2.9.4

[Qemu-devel] [PATCH 1/6] hw/ide: Convert DeviceClass init to realize

[Mao Zhongyi]

Replace init with realize in IDEDeviceClass, which has errp
as a parameter. So all the implementations now use error_setg
instead of error_report for reporting error.

Cc: John Snow <jsnow@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>

Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
---
 hw/ide/core.c             |  7 ++--
 hw/ide/qdev.c             | 86 +++++++++++++++++++++++------------------------
 include/hw/ide/internal.h |  5 +--
 3 files changed, 49 insertions(+), 49 deletions(-)

diff --git a/hw/ide/core.c b/hw/ide/core.c
index 0b48b64..7c86fc7 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -34,6 +34,7 @@
 #include "hw/block/block.h"
 #include "sysemu/block-backend.h"
 #include "qemu/cutils.h"
+#include "qemu/error-report.h"
 
 #include "hw/ide/internal.h"
 
@@ -2398,7 +2399,7 @@ int ide_init_drive(IDEState *s, BlockBackend *blk, IDEDriveKind kind,
                    const char *version, const char *serial, const char *model,
                    uint64_t wwn,
                    uint32_t cylinders, uint32_t heads, uint32_t secs,
-                   int chs_trans)
+                   int chs_trans, Error **errp)
 {
     uint64_t nb_sectors;
 
@@ -2423,11 +2424,11 @@ int ide_init_drive(IDEState *s, BlockBackend *blk, IDEDriveKind kind,
         blk_set_guest_block_size(blk, 2048);
     } else {
         if (!blk_is_inserted(s->blk)) {
-            error_report("Device needs media, but drive is empty");
+            error_setg(errp, "Device needs media, but drive is empty");
             return -1;
         }
         if (blk_is_read_only(blk)) {
-            error_report("Can't use a read-only drive");
+            error_setg(errp, "Can't use a read-only drive");
             return -1;
         }
         blk_set_dev_ops(blk, &ide_hd_block_ops, s);
diff --git a/hw/ide/qdev.c b/hw/ide/qdev.c
index cc2f5bd..d60ac25 100644
--- a/hw/ide/qdev.c
+++ b/hw/ide/qdev.c
@@ -80,7 +80,7 @@ static char *idebus_get_fw_dev_path(DeviceState *dev)
     return g_strdup(path);
 }
 
-static int ide_qdev_init(DeviceState *qdev)
+static void ide_qdev_realize(DeviceState *qdev, Error **errp)
 {
     IDEDevice *dev = IDE_DEVICE(qdev);
     IDEDeviceClass *dc = IDE_DEVICE_GET_CLASS(dev);
@@ -91,34 +91,31 @@ static int ide_qdev_init(DeviceState *qdev)
     }
 
     if (dev->unit >= bus->max_units) {
-        error_report("Can't create IDE unit %d, bus supports only %d units",
+        error_setg(errp, "Can't create IDE unit %d, bus supports only %d units",
                      dev->unit, bus->max_units);
-        goto err;
+        return;
     }
 
     switch (dev->unit) {
     case 0:
         if (bus->master) {
-            error_report("IDE unit %d is in use", dev->unit);
-            goto err;
+            error_setg(errp, "IDE unit %d is in use", dev->unit);
+            return;
         }
         bus->master = dev;
         break;
     case 1:
         if (bus->slave) {
-            error_report("IDE unit %d is in use", dev->unit);
-            goto err;
+            error_setg(errp, "IDE unit %d is in use", dev->unit);
+            return;
         }
         bus->slave = dev;
         break;
     default:
-        error_report("Invalid IDE unit %d", dev->unit);
-        goto err;
+        error_setg(errp, "Invalid IDE unit %d", dev->unit);
+        return;
     }
-    return dc->init(dev);
-
-err:
-    return -1;
+    dc->realize(dev, errp);
 }
 
 IDEDevice *ide_create_drive(IDEBus *bus, int unit, DriveInfo *drive)
@@ -159,7 +156,7 @@ typedef struct IDEDrive {
     IDEDevice dev;
 } IDEDrive;
 
-static int ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind)
+static void ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind, Error **errp)
 {
     IDEBus *bus = DO_UPCAST(IDEBus, qbus, dev->qdev.parent_bus);
     IDEState *s = bus->ifs + dev->unit;
@@ -168,8 +165,8 @@ static int ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind)
 
     if (!dev->conf.blk) {
         if (kind != IDE_CD) {
-            error_report("No drive specified");
-            return -1;
+            error_setg(errp, "No drive specified");
+            return;
         } else {
             /* Anonymous BlockBackend for an empty drive */
             dev->conf.blk = blk_new(0, BLK_PERM_ALL);
@@ -182,36 +179,36 @@ static int ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind)
         dev->conf.discard_granularity = 512;
     } else if (dev->conf.discard_granularity &&
                dev->conf.discard_granularity != 512) {
-        error_report("discard_granularity must be 512 for ide");
-        return -1;
+        error_setg(errp, "discard_granularity must be 512 for ide");
+        return;
     }
 
     blkconf_blocksizes(&dev->conf);
     if (dev->conf.logical_block_size != 512) {
-        error_report("logical_block_size must be 512 for IDE");
-        return -1;
+        error_setg(errp, "logical_block_size must be 512 for IDE");
+        return;
     }
 
     blkconf_serial(&dev->conf, &dev->serial);
     if (kind != IDE_CD) {
         blkconf_geometry(&dev->conf, &dev->chs_trans, 65535, 16, 255, &err);
         if (err) {
-            error_report_err(err);
-            return -1;
+            error_propagate(errp, err);
+            return;
         }
     }
     blkconf_apply_backend_options(&dev->conf, kind == IDE_CD, kind != IDE_CD,
                                   &err);
     if (err) {
-        error_report_err(err);
-        return -1;
+        error_propagate(errp, err);
+        return;
     }
 
     if (ide_init_drive(s, dev->conf.blk, kind,
                        dev->version, dev->serial, dev->model, dev->wwn,
                        dev->conf.cyls, dev->conf.heads, dev->conf.secs,
-                       dev->chs_trans) < 0) {
-        return -1;
+                       dev->chs_trans, errp) < 0) {
+        return;
     }
 
     if (!dev->version) {
@@ -223,8 +220,6 @@ static int ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind)
 
     add_boot_device_path(dev->conf.bootindex, &dev->qdev,
                          dev->unit ? "/disk@1" : "/disk@0");
-
-    return 0;
 }
 
 static void ide_dev_get_bootindex(Object *obj, Visitor *v, const char *name,
@@ -270,17 +265,17 @@ static void ide_dev_instance_init(Object *obj)
     object_property_set_int(obj, -1, "bootindex", NULL);
 }
 
-static int ide_hd_initfn(IDEDevice *dev)
+static void ide_hd_realize(IDEDevice *dev, Error **errp)
 {
-    return ide_dev_initfn(dev, IDE_HD);
+    ide_dev_initfn(dev, IDE_HD, errp);
 }
 
-static int ide_cd_initfn(IDEDevice *dev)
+static void ide_cd_realize(IDEDevice *dev, Error **errp)
 {
-    return ide_dev_initfn(dev, IDE_CD);
+    ide_dev_initfn(dev, IDE_CD, errp);
 }
 
-static int ide_drive_initfn(IDEDevice *dev)
+static void ide_drive_realize(IDEDevice *dev, Error **errp)
 {
     DriveInfo *dinfo = NULL;
 
@@ -288,7 +283,7 @@ static int ide_drive_initfn(IDEDevice *dev)
         dinfo = blk_legacy_dinfo(dev->conf.blk);
     }
 
-    return ide_dev_initfn(dev, dinfo && dinfo->media_cd ? IDE_CD : IDE_HD);
+    ide_dev_initfn(dev, dinfo && dinfo->media_cd ? IDE_CD : IDE_HD, errp);
 }
 
 #define DEFINE_IDE_DEV_PROPERTIES()                     \
@@ -311,10 +306,11 @@ static void ide_hd_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     IDEDeviceClass *k = IDE_DEVICE_CLASS(klass);
-    k->init = ide_hd_initfn;
+
+    k->realize  = ide_hd_realize;
     dc->fw_name = "drive";
-    dc->desc = "virtual IDE disk";
-    dc->props = ide_hd_properties;
+    dc->desc    = "virtual IDE disk";
+    dc->props   = ide_hd_properties;
 }
 
 static const TypeInfo ide_hd_info = {
@@ -333,10 +329,11 @@ static void ide_cd_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     IDEDeviceClass *k = IDE_DEVICE_CLASS(klass);
-    k->init = ide_cd_initfn;
+
+    k->realize  = ide_cd_realize;
     dc->fw_name = "drive";
-    dc->desc = "virtual IDE CD-ROM";
-    dc->props = ide_cd_properties;
+    dc->desc    = "virtual IDE CD-ROM";
+    dc->props   = ide_cd_properties;
 }
 
 static const TypeInfo ide_cd_info = {
@@ -355,10 +352,11 @@ static void ide_drive_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     IDEDeviceClass *k = IDE_DEVICE_CLASS(klass);
-    k->init = ide_drive_initfn;
+
+    k->realize  = ide_drive_realize;
     dc->fw_name = "drive";
-    dc->desc = "virtual IDE disk or CD-ROM (legacy)";
-    dc->props = ide_drive_properties;
+    dc->desc    = "virtual IDE disk or CD-ROM (legacy)";
+    dc->props   = ide_drive_properties;
 }
 
 static const TypeInfo ide_drive_info = {
@@ -371,7 +369,7 @@ static const TypeInfo ide_drive_info = {
 static void ide_device_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *k = DEVICE_CLASS(klass);
-    k->init = ide_qdev_init;
+    k->realize = ide_qdev_realize;
     set_bit(DEVICE_CATEGORY_STORAGE, k->categories);
     k->bus_type = TYPE_IDE_BUS;
     k->props = ide_props;
diff --git a/include/hw/ide/internal.h b/include/hw/ide/internal.h
index 482a951..5ebb4c9 100644
--- a/include/hw/ide/internal.h
+++ b/include/hw/ide/internal.h
@@ -12,6 +12,7 @@
 #include "sysemu/sysemu.h"
 #include "hw/block/block.h"
 #include "block/scsi.h"
+#include "qapi/error.h"
 
 /* debug IDE devices */
 //#define DEBUG_IDE
@@ -495,7 +496,7 @@ struct IDEBus {
 
 typedef struct IDEDeviceClass {
     DeviceClass parent_class;
-    int (*init)(IDEDevice *dev);
+    void (*realize)(IDEDevice *dev, Error **errp);
 } IDEDeviceClass;
 
 struct IDEDevice {
@@ -605,7 +606,7 @@ int ide_init_drive(IDEState *s, BlockBackend *blk, IDEDriveKind kind,
                    const char *version, const char *serial, const char *model,
                    uint64_t wwn,
                    uint32_t cylinders, uint32_t heads, uint32_t secs,
-                   int chs_trans);
+                   int chs_trans, Error **errp);
 void ide_init2(IDEBus *bus, qemu_irq irq);
 void ide_exit(IDEState *s);
 void ide_init_ioport(IDEBus *bus, ISADevice *isa, int iobase, int iobase2);
-- 
2.9.4

[Qemu-devel] [PATCH 2/6] hw/block/fdc: Convert to realize

[Mao Zhongyi]

Convert floppy_drive_init() to realize and rename it to
floppy_drive_realize().

Cc: John Snow <jsnow@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>

Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
---
 hw/block/fdc.c | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/hw/block/fdc.c b/hw/block/fdc.c
index 4011290..02f4a46 100644
--- a/hw/block/fdc.c
+++ b/hw/block/fdc.c
@@ -517,7 +517,7 @@ static Property floppy_drive_properties[] = {
     DEFINE_PROP_END_OF_LIST(),
 };
 
-static int floppy_drive_init(DeviceState *qdev)
+static void floppy_drive_realize(DeviceState *qdev, Error **errp)
 {
     FloppyDrive *dev = FLOPPY_DRIVE(qdev);
     FloppyBus *bus = FLOPPY_BUS(qdev->parent_bus);
@@ -535,15 +535,15 @@ static int floppy_drive_init(DeviceState *qdev)
     }
 
     if (dev->unit >= MAX_FD) {
-        error_report("Can't create floppy unit %d, bus supports only %d units",
-                     dev->unit, MAX_FD);
-        return -1;
+        error_setg(errp, "Can't create floppy unit %d, bus supports "
+                   "only %d units", dev->unit, MAX_FD);
+        return;
     }
 
     drive = get_drv(bus->fdc, dev->unit);
     if (drive->blk) {
-        error_report("Floppy unit %d is in use", dev->unit);
-        return -1;
+        error_setg(errp, "Floppy unit %d is in use", dev->unit);
+        return;
     }
 
     if (!dev->conf.blk) {
@@ -557,8 +557,9 @@ static int floppy_drive_init(DeviceState *qdev)
     if (dev->conf.logical_block_size != 512 ||
         dev->conf.physical_block_size != 512)
     {
-        error_report("Physical and logical block size must be 512 for floppy");
-        return -1;
+        error_setg(errp, "Physical and logical block size must "
+                   "be 512 for floppy");
+        return;
     }
 
     /* rerror/werror aren't supported by fdc and therefore not even registered
@@ -570,20 +571,20 @@ static int floppy_drive_init(DeviceState *qdev)
     blkconf_apply_backend_options(&dev->conf, blk_is_read_only(dev->conf.blk),
                                   false, &local_err);
     if (local_err) {
-        error_report_err(local_err);
-        return -1;
+        error_propagate(errp, local_err);
+        return;
     }
 
     /* 'enospc' is the default for -drive, 'report' is what blk_new() gives us
      * for empty drives. */
     if (blk_get_on_error(dev->conf.blk, 0) != BLOCKDEV_ON_ERROR_ENOSPC &&
         blk_get_on_error(dev->conf.blk, 0) != BLOCKDEV_ON_ERROR_REPORT) {
-        error_report("fdc doesn't support drive option werror");
-        return -1;
+        error_setg(errp, "fdc doesn't support drive option werror");
+        return;
     }
     if (blk_get_on_error(dev->conf.blk, 1) != BLOCKDEV_ON_ERROR_REPORT) {
-        error_report("fdc doesn't support drive option rerror");
-        return -1;
+        error_setg(errp, "fdc doesn't support drive option rerror");
+        return;
     }
 
     drive->conf = &dev->conf;
@@ -599,14 +600,12 @@ static int floppy_drive_init(DeviceState *qdev)
     dev->type = drive->drive;
 
     fd_revalidate(drive);
-
-    return 0;
 }
 
 static void floppy_drive_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *k = DEVICE_CLASS(klass);
-    k->init = floppy_drive_init;
+    k->realize = floppy_drive_realize;
     set_bit(DEVICE_CATEGORY_STORAGE, k->categories);
     k->bus_type = TYPE_FLOPPY_BUS;
     k->props = floppy_drive_properties;
-- 
2.9.4

[Qemu-devel] [PATCH 3/6] hw/block/nvme: Convert to realize

[Mao Zhongyi]

Convert nvme_init() to realize and rename it to nvme_realize().

Cc: Keith Busch <keith.busch@intel.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>

Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
---
 hw/block/nvme.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index 6071dc1..43c60ab 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -920,7 +920,7 @@ static const MemoryRegionOps nvme_cmb_ops = {
     },
 };
 
-static int nvme_init(PCIDevice *pci_dev)
+static void nvme_realize(PCIDevice *pci_dev, Error **errp)
 {
     NvmeCtrl *n = NVME(pci_dev);
     NvmeIdCtrl *id = &n->id_ctrl;
@@ -931,24 +931,27 @@ static int nvme_init(PCIDevice *pci_dev)
     Error *local_err = NULL;
 
     if (!n->conf.blk) {
-        return -1;
+        error_setg(errp, "drive property not set");
+        return;
     }
 
     bs_size = blk_getlength(n->conf.blk);
     if (bs_size < 0) {
-        return -1;
+        error_setg(errp, "could not get backing file size");
+        return;
     }
 
     blkconf_serial(&n->conf, &n->serial);
     if (!n->serial) {
-        return -1;
+        error_setg(errp, "serial property not set");
+        return;
     }
     blkconf_blocksizes(&n->conf);
     blkconf_apply_backend_options(&n->conf, blk_is_read_only(n->conf.blk),
                                   false, &local_err);
     if (local_err) {
-        error_report_err(local_err);
-        return -1;
+        error_propagate(errp, local_err);
+        return;
     }
 
     pci_conf = pci_dev->config;
@@ -1046,7 +1049,6 @@ static int nvme_init(PCIDevice *pci_dev)
             cpu_to_le64(n->ns_size >>
                 id_ns->lbaf[NVME_ID_NS_FLBAS_INDEX(ns->id_ns.flbas)].ds);
     }
-    return 0;
 }
 
 static void nvme_exit(PCIDevice *pci_dev)
@@ -1081,7 +1083,7 @@ static void nvme_class_init(ObjectClass *oc, void *data)
     DeviceClass *dc = DEVICE_CLASS(oc);
     PCIDeviceClass *pc = PCI_DEVICE_CLASS(oc);
 
-    pc->init = nvme_init;
+    pc->realize = nvme_realize;
     pc->exit = nvme_exit;
     pc->class_id = PCI_CLASS_STORAGE_EXPRESS;
     pc->vendor_id = PCI_VENDOR_ID_INTEL;
-- 
2.9.4

[Qemu-devel] [PATCH 4/6] hw/block: Fix the return type

[Mao Zhongyi]

When the function no success value to transmit, it usually make the
function return void. It has turned out not to be a success, because
it means that the extra local_err variable and error_propagate() will
be needed. It leads to cumbersome code, therefore, transmit success/
failure in the return value is worth.

So fix the return type of blkconf_apply_backend_options(),
blkconf_geometry() and virtio_blk_data_plane_create() to avoid it.

Cc: John Snow <jsnow@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>

Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
---
 hw/block/block.c                | 21 ++++++++++++---------
 hw/block/dataplane/virtio-blk.c | 16 +++++++++-------
 hw/block/dataplane/virtio-blk.h |  6 +++---
 include/hw/block/block.h        | 10 +++++-----
 4 files changed, 29 insertions(+), 24 deletions(-)

diff --git a/hw/block/block.c b/hw/block/block.c
index 27878d0..717bd0e 100644
--- a/hw/block/block.c
+++ b/hw/block/block.c
@@ -51,8 +51,8 @@ void blkconf_blocksizes(BlockConf *conf)
     }
 }
 
-void blkconf_apply_backend_options(BlockConf *conf, bool readonly,
-                                   bool resizable, Error **errp)
+int blkconf_apply_backend_options(BlockConf *conf, bool readonly,
+                                  bool resizable, Error **errp)
 {
     BlockBackend *blk = conf->blk;
     BlockdevOnError rerror, werror;
@@ -76,7 +76,7 @@ void blkconf_apply_backend_options(BlockConf *conf, bool readonly,
 
     ret = blk_set_perm(blk, perm, shared_perm, errp);
     if (ret < 0) {
-        return;
+        return -1;
     }
 
     switch (conf->wce) {
@@ -99,11 +99,13 @@ void blkconf_apply_backend_options(BlockConf *conf, bool readonly,
 
     blk_set_enable_write_cache(blk, wce);
     blk_set_on_error(blk, rerror, werror);
+
+    return 0;
 }
 
-void blkconf_geometry(BlockConf *conf, int *ptrans,
-                      unsigned cyls_max, unsigned heads_max, unsigned secs_max,
-                      Error **errp)
+int blkconf_geometry(BlockConf *conf, int *ptrans,
+                     unsigned cyls_max, unsigned heads_max, unsigned secs_max,
+                     Error **errp)
 {
     DriveInfo *dinfo;
 
@@ -129,15 +131,16 @@ void blkconf_geometry(BlockConf *conf, int *ptrans,
     if (conf->cyls || conf->heads || conf->secs) {
         if (conf->cyls < 1 || conf->cyls > cyls_max) {
             error_setg(errp, "cyls must be between 1 and %u", cyls_max);
-            return;
+            return -1;
         }
         if (conf->heads < 1 || conf->heads > heads_max) {
             error_setg(errp, "heads must be between 1 and %u", heads_max);
-            return;
+            return -1;
         }
         if (conf->secs < 1 || conf->secs > secs_max) {
             error_setg(errp, "secs must be between 1 and %u", secs_max);
-            return;
+            return -1;
         }
     }
+    return 0;
 }
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 5556f0e..619bc5e 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -76,9 +76,9 @@ static void notify_guest_bh(void *opaque)
 }
 
 /* Context: QEMU global mutex held */
-void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
-                                  VirtIOBlockDataPlane **dataplane,
-                                  Error **errp)
+int virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
+                                 VirtIOBlockDataPlane **dataplane,
+                                 Error **errp)
 {
     VirtIOBlockDataPlane *s;
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
@@ -91,11 +91,11 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
             error_setg(errp,
                        "device is incompatible with iothread "
                        "(transport does not support notifiers)");
-            return;
+            return -1;
         }
         if (!virtio_device_ioeventfd_enabled(vdev)) {
             error_setg(errp, "ioeventfd is required for iothread");
-            return;
+            return -1;
         }
 
         /* If dataplane is (re-)enabled while the guest is running there could
@@ -103,12 +103,12 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
          */
         if (blk_op_is_blocked(conf->conf.blk, BLOCK_OP_TYPE_DATAPLANE, errp)) {
             error_prepend(errp, "cannot start virtio-blk dataplane: ");
-            return;
+            return -1;
         }
     }
     /* Don't try if transport does not support notifiers. */
     if (!virtio_device_ioeventfd_enabled(vdev)) {
-        return;
+        return -1;
     }
 
     s = g_new0(VirtIOBlockDataPlane, 1);
@@ -126,6 +126,8 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
     s->batch_notify_vqs = bitmap_new(conf->num_queues);
 
     *dataplane = s;
+
+    return 0;
 }
 
 /* Context: QEMU global mutex held */
diff --git a/hw/block/dataplane/virtio-blk.h b/hw/block/dataplane/virtio-blk.h
index db3f47b..d25773d 100644
--- a/hw/block/dataplane/virtio-blk.h
+++ b/hw/block/dataplane/virtio-blk.h
@@ -19,9 +19,9 @@
 
 typedef struct VirtIOBlockDataPlane VirtIOBlockDataPlane;
 
-void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
-                                  VirtIOBlockDataPlane **dataplane,
-                                  Error **errp);
+int virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
+                                 VirtIOBlockDataPlane **dataplane,
+                                 Error **errp);
 void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s);
 void virtio_blk_data_plane_notify(VirtIOBlockDataPlane *s, VirtQueue *vq);
 
diff --git a/include/hw/block/block.h b/include/hw/block/block.h
index f3f6e8e..66117c6 100644
--- a/include/hw/block/block.h
+++ b/include/hw/block/block.h
@@ -72,12 +72,12 @@ static inline unsigned int get_physical_block_exp(BlockConf *conf)
 /* Configuration helpers */
 
 void blkconf_serial(BlockConf *conf, char **serial);
-void blkconf_geometry(BlockConf *conf, int *trans,
-                      unsigned cyls_max, unsigned heads_max, unsigned secs_max,
-                      Error **errp);
+int blkconf_geometry(BlockConf *conf, int *trans,
+                     unsigned cyls_max, unsigned heads_max, unsigned secs_max,
+                     Error **errp);
 void blkconf_blocksizes(BlockConf *conf);
-void blkconf_apply_backend_options(BlockConf *conf, bool readonly,
-                                   bool resizable, Error **errp);
+int blkconf_apply_backend_options(BlockConf *conf, bool readonly,
+                                  bool resizable, Error **errp);
 
 /* Hard disk geometry */
 
-- 
2.9.4

[Qemu-devel] [PATCH 5/6] hw/block: Use errp directly rather than local_err

[Mao Zhongyi]

Pass the error message to errp directly rather than the local
variable local_err and propagate it to errp via error_propagate().

Cc: John Snow <jsnow@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>

Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
---
 hw/block/fdc.c        | 17 ++++++-----------
 hw/block/nvme.c       |  8 +++-----
 hw/block/virtio-blk.c | 17 +++++------------
 hw/ide/qdev.c         | 12 ++++--------
 hw/scsi/scsi-disk.c   | 13 ++++---------
 hw/usb/dev-storage.c  |  9 +++------
 6 files changed, 25 insertions(+), 51 deletions(-)

diff --git a/hw/block/fdc.c b/hw/block/fdc.c
index 02f4a46..e6398c3 100644
--- a/hw/block/fdc.c
+++ b/hw/block/fdc.c
@@ -473,16 +473,13 @@ static void fd_revalidate(FDrive *drv)
 static void fd_change_cb(void *opaque, bool load, Error **errp)
 {
     FDrive *drive = opaque;
-    Error *local_err = NULL;
 
     if (!load) {
         blk_set_perm(drive->blk, 0, BLK_PERM_ALL, &error_abort);
     } else {
-        blkconf_apply_backend_options(drive->conf,
-                                      blk_is_read_only(drive->blk), false,
-                                      &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        if (blkconf_apply_backend_options(drive->conf,
+                                          blk_is_read_only(drive->blk),
+                                          false, errp) < 0) {
             return;
         }
     }
@@ -522,7 +519,6 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp)
     FloppyDrive *dev = FLOPPY_DRIVE(qdev);
     FloppyBus *bus = FLOPPY_BUS(qdev->parent_bus);
     FDrive *drive;
-    Error *local_err = NULL;
     int ret;
 
     if (dev->unit == -1) {
@@ -568,10 +564,9 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp)
     dev->conf.rerror = BLOCKDEV_ON_ERROR_AUTO;
     dev->conf.werror = BLOCKDEV_ON_ERROR_AUTO;
 
-    blkconf_apply_backend_options(&dev->conf, blk_is_read_only(dev->conf.blk),
-                                  false, &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
+    if (blkconf_apply_backend_options(&dev->conf,
+                                      blk_is_read_only(dev->conf.blk),
+                                      false, errp) < 0) {
         return;
     }
 
diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index 43c60ab..2a9d03b 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -928,7 +928,6 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
     int i;
     int64_t bs_size;
     uint8_t *pci_conf;
-    Error *local_err = NULL;
 
     if (!n->conf.blk) {
         error_setg(errp, "drive property not set");
@@ -947,10 +946,9 @@ static void nvme_realize(PCIDevice *pci_dev, Error **errp)
         return;
     }
     blkconf_blocksizes(&n->conf);
-    blkconf_apply_backend_options(&n->conf, blk_is_read_only(n->conf.blk),
-                                  false, &local_err);
-    if (local_err) {
-        error_propagate(errp, local_err);
+    if (blkconf_apply_backend_options(&n->conf,
+                                      blk_is_read_only(n->conf.blk),
+                                      false, errp) < 0) {
         return;
     }
 
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index b750bd8..5a4e9d2 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -911,7 +911,6 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VirtIOBlock *s = VIRTIO_BLK(dev);
     VirtIOBlkConf *conf = &s->conf;
-    Error *err = NULL;
     unsigned i;
 
     if (!conf->conf.blk) {
@@ -928,17 +927,13 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
     }
 
     blkconf_serial(&conf->conf, &conf->serial);
-    blkconf_apply_backend_options(&conf->conf,
-                                  blk_is_read_only(conf->conf.blk), true,
-                                  &err);
-    if (err) {
-        error_propagate(errp, err);
+    if (blkconf_apply_backend_options(&conf->conf,
+                                      blk_is_read_only(conf->conf.blk),
+                                      true, errp) < 0) {
         return;
     }
     s->original_wce = blk_enable_write_cache(conf->conf.blk);
-    blkconf_geometry(&conf->conf, NULL, 65535, 255, 255, &err);
-    if (err) {
-        error_propagate(errp, err);
+    if (blkconf_geometry(&conf->conf, NULL, 65535, 255, 255, errp) < 0) {
         return;
     }
     blkconf_blocksizes(&conf->conf);
@@ -953,9 +948,7 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
     for (i = 0; i < conf->num_queues; i++) {
         virtio_add_queue(vdev, 128, virtio_blk_handle_output);
     }
-    virtio_blk_data_plane_create(vdev, conf, &s->dataplane, &err);
-    if (err != NULL) {
-        error_propagate(errp, err);
+    if (virtio_blk_data_plane_create(vdev, conf, &s->dataplane, errp) < 0) {
         virtio_cleanup(vdev);
         return;
     }
diff --git a/hw/ide/qdev.c b/hw/ide/qdev.c
index d60ac25..880b965 100644
--- a/hw/ide/qdev.c
+++ b/hw/ide/qdev.c
@@ -160,7 +160,6 @@ static void ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind, Error **errp)
 {
     IDEBus *bus = DO_UPCAST(IDEBus, qbus, dev->qdev.parent_bus);
     IDEState *s = bus->ifs + dev->unit;
-    Error *err = NULL;
     int ret;
 
     if (!dev->conf.blk) {
@@ -191,16 +190,13 @@ static void ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind, Error **errp)
 
     blkconf_serial(&dev->conf, &dev->serial);
     if (kind != IDE_CD) {
-        blkconf_geometry(&dev->conf, &dev->chs_trans, 65535, 16, 255, &err);
-        if (err) {
-            error_propagate(errp, err);
+        if (blkconf_geometry(&dev->conf, &dev->chs_trans, 65535, 16, 255,
+                             errp) < 0) {
             return;
         }
     }
-    blkconf_apply_backend_options(&dev->conf, kind == IDE_CD, kind != IDE_CD,
-                                  &err);
-    if (err) {
-        error_propagate(errp, err);
+    if (blkconf_apply_backend_options(&dev->conf, kind == IDE_CD,
+                                      kind != IDE_CD, errp) < 0) {
         return;
     }
 
diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 5f1e5e8..6833819 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -2306,7 +2306,6 @@ static void scsi_disk_unit_attention_reported(SCSIDevice *dev)
 static void scsi_realize(SCSIDevice *dev, Error **errp)
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, dev);
-    Error *err = NULL;
 
     if (!s->qdev.conf.blk) {
         error_setg(errp, "drive property not set");
@@ -2322,17 +2321,13 @@ static void scsi_realize(SCSIDevice *dev, Error **errp)
     blkconf_serial(&s->qdev.conf, &s->serial);
     blkconf_blocksizes(&s->qdev.conf);
     if (dev->type == TYPE_DISK) {
-        blkconf_geometry(&dev->conf, NULL, 65535, 255, 255, &err);
-        if (err) {
-            error_propagate(errp, err);
+        if (blkconf_geometry(&dev->conf, NULL, 65535, 255, 255, errp) < 0) {
             return;
         }
     }
-    blkconf_apply_backend_options(&dev->conf,
-                                  blk_is_read_only(s->qdev.conf.blk),
-                                  dev->type == TYPE_DISK, &err);
-    if (err) {
-        error_propagate(errp, err);
+    if (blkconf_apply_backend_options(&dev->conf,
+                                      blk_is_read_only(s->qdev.conf.blk),
+                                      dev->type == TYPE_DISK, errp) < 0) {
         return;
     }
 
diff --git a/hw/usb/dev-storage.c b/hw/usb/dev-storage.c
index 8a61ec9..bd88d6e 100644
--- a/hw/usb/dev-storage.c
+++ b/hw/usb/dev-storage.c
@@ -601,7 +601,6 @@ static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
     MSDState *s = USB_STORAGE_DEV(dev);
     BlockBackend *blk = s->conf.blk;
     SCSIDevice *scsi_dev;
-    Error *err = NULL;
 
     if (!blk) {
         error_setg(errp, "drive property not set");
@@ -610,9 +609,8 @@ static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
 
     blkconf_serial(&s->conf, &dev->serial);
     blkconf_blocksizes(&s->conf);
-    blkconf_apply_backend_options(&s->conf, blk_is_read_only(blk), true, &err);
-    if (err) {
-        error_propagate(errp, err);
+    if (blkconf_apply_backend_options(&s->conf, blk_is_read_only(blk),
+                                      true, errp) < 0) {
         return;
     }
 
@@ -636,10 +634,9 @@ static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
                  &usb_msd_scsi_info_storage, NULL);
     scsi_dev = scsi_bus_legacy_add_drive(&s->bus, blk, 0, !!s->removable,
                                          s->conf.bootindex, dev->serial,
-                                         &err);
+                                         errp);
     blk_unref(blk);
     if (!scsi_dev) {
-        error_propagate(errp, err);
         return;
     }
     usb_msd_handle_reset(dev);
-- 
2.9.4

[Qemu-devel] [PATCH 6/6] dev-storage: Fix the unusual function name

[Mao Zhongyi]

The function name of usb_msd_{realize,unrealize}_*,
usb_msd_class_initfn_* are unusual. Rename it to
usb_msd_*_{realize,unrealize}, usb_msd_class_*_initfn.

Cc: Gerd Hoffmann <kraxel@redhat.com>

Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
---
 hw/usb/dev-storage.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/hw/usb/dev-storage.c b/hw/usb/dev-storage.c
index bd88d6e..599c536 100644
--- a/hw/usb/dev-storage.c
+++ b/hw/usb/dev-storage.c
@@ -596,7 +596,7 @@ static void usb_msd_unrealize_storage(USBDevice *dev, Error **errp)
     object_unref(OBJECT(&s->bus));
 }
 
-static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
+static void usb_msd_storage_realize(USBDevice *dev, Error **errp)
 {
     MSDState *s = USB_STORAGE_DEV(dev);
     BlockBackend *blk = s->conf.blk;
@@ -643,14 +643,14 @@ static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
     s->scsi_dev = scsi_dev;
 }
 
-static void usb_msd_unrealize_bot(USBDevice *dev, Error **errp)
+static void usb_msd_bot_unrealize(USBDevice *dev, Error **errp)
 {
     MSDState *s = USB_STORAGE_DEV(dev);
 
     object_unref(OBJECT(&s->bus));
 }
 
-static void usb_msd_realize_bot(USBDevice *dev, Error **errp)
+static void usb_msd_bot_realize(USBDevice *dev, Error **errp)
 {
     MSDState *s = USB_STORAGE_DEV(dev);
     DeviceState *d = DEVICE(dev);
@@ -764,12 +764,12 @@ static void usb_msd_class_initfn_common(ObjectClass *klass, void *data)
     dc->vmsd = &vmstate_usb_msd;
 }
 
-static void usb_msd_class_initfn_storage(ObjectClass *klass, void *data)
+static void usb_msd_class_storage_initfn(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     USBDeviceClass *uc = USB_DEVICE_CLASS(klass);
 
-    uc->realize = usb_msd_realize_storage;
+    uc->realize = usb_msd_storage_realize;
     uc->unrealize = usb_msd_unrealize_storage;
     dc->props = msd_properties;
 }
@@ -828,26 +828,26 @@ static void usb_msd_instance_init(Object *obj)
     object_property_set_int(obj, -1, "bootindex", NULL);
 }
 
-static void usb_msd_class_initfn_bot(ObjectClass *klass, void *data)
+static void usb_msd_class_bot_initfn(ObjectClass *klass, void *data)
 {
     USBDeviceClass *uc = USB_DEVICE_CLASS(klass);
 
-    uc->realize = usb_msd_realize_bot;
-    uc->unrealize = usb_msd_unrealize_bot;
+    uc->realize = usb_msd_bot_realize;
+    uc->unrealize = usb_msd_bot_unrealize;
     uc->attached_settable = true;
 }
 
 static const TypeInfo msd_info = {
     .name          = "usb-storage",
     .parent        = TYPE_USB_STORAGE,
-    .class_init    = usb_msd_class_initfn_storage,
+    .class_init    = usb_msd_class_storage_initfn,
     .instance_init = usb_msd_instance_init,
 };
 
 static const TypeInfo bot_info = {
     .name          = "usb-bot",
     .parent        = TYPE_USB_STORAGE,
-    .class_init    = usb_msd_class_initfn_bot,
+    .class_init    = usb_msd_class_bot_initfn,
 };
 
 static void usb_msd_register_types(void)
-- 
2.9.4

Re: [Qemu-devel] [PATCH 4/6] hw/block: Fix the return type

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 1930 bytes --]

On Wed, Jul 26, 2017 at 08:02:53PM +0800, Mao Zhongyi wrote:
> When the function no success value to transmit, it usually make the
> function return void. It has turned out not to be a success, because
> it means that the extra local_err variable and error_propagate() will
> be needed. It leads to cumbersome code, therefore, transmit success/
> failure in the return value is worth.
> 
> So fix the return type of blkconf_apply_backend_options(),
> blkconf_geometry() and virtio_blk_data_plane_create() to avoid it.
> 
> Cc: John Snow <jsnow@redhat.com>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Max Reitz <mreitz@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> 
> Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
> ---
>  hw/block/block.c                | 21 ++++++++++++---------
>  hw/block/dataplane/virtio-blk.c | 16 +++++++++-------
>  hw/block/dataplane/virtio-blk.h |  6 +++---
>  include/hw/block/block.h        | 10 +++++-----
>  4 files changed, 29 insertions(+), 24 deletions(-)
> 
> diff --git a/hw/block/block.c b/hw/block/block.c
> index 27878d0..717bd0e 100644
> --- a/hw/block/block.c
> +++ b/hw/block/block.c
> @@ -51,8 +51,8 @@ void blkconf_blocksizes(BlockConf *conf)
>      }
>  }
>  
> -void blkconf_apply_backend_options(BlockConf *conf, bool readonly,
> -                                   bool resizable, Error **errp)
> +int blkconf_apply_backend_options(BlockConf *conf, bool readonly,
> +                                  bool resizable, Error **errp)

I'm not a fan of these changes because it makes inconsistencies between
the return value and the errp argument possible (e.g. returning success
but setting errp, or returning failure without setting errp).

If you really want to do this please use bool as the return type instead
of int.  int can be abused to return error information that should
really be in the Error object.

Stefan

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 455 bytes --]

Re: [Qemu-devel] [PATCH 4/6] hw/block: Fix the return type

[Markus Armbruster]

Stefan Hajnoczi <stefanha@gmail.com> writes:

> On Wed, Jul 26, 2017 at 08:02:53PM +0800, Mao Zhongyi wrote:
>> When the function no success value to transmit, it usually make the
>> function return void. It has turned out not to be a success, because
>> it means that the extra local_err variable and error_propagate() will
>> be needed. It leads to cumbersome code, therefore, transmit success/
>> failure in the return value is worth.
>> 
>> So fix the return type of blkconf_apply_backend_options(),
>> blkconf_geometry() and virtio_blk_data_plane_create() to avoid it.
>> 
>> Cc: John Snow <jsnow@redhat.com>
>> Cc: Kevin Wolf <kwolf@redhat.com>
>> Cc: Max Reitz <mreitz@redhat.com>
>> Cc: Stefan Hajnoczi <stefanha@redhat.com>
>> 
>> Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
>> ---
>>  hw/block/block.c                | 21 ++++++++++++---------
>>  hw/block/dataplane/virtio-blk.c | 16 +++++++++-------
>>  hw/block/dataplane/virtio-blk.h |  6 +++---
>>  include/hw/block/block.h        | 10 +++++-----
>>  4 files changed, 29 insertions(+), 24 deletions(-)
>> 
>> diff --git a/hw/block/block.c b/hw/block/block.c
>> index 27878d0..717bd0e 100644
>> --- a/hw/block/block.c
>> +++ b/hw/block/block.c
>> @@ -51,8 +51,8 @@ void blkconf_blocksizes(BlockConf *conf)
>>      }
>>  }
>>  
>> -void blkconf_apply_backend_options(BlockConf *conf, bool readonly,
>> -                                   bool resizable, Error **errp)
>> +int blkconf_apply_backend_options(BlockConf *conf, bool readonly,
>> +                                  bool resizable, Error **errp)
>
> I'm not a fan of these changes because it makes inconsistencies between
> the return value and the errp argument possible (e.g. returning success
> but setting errp, or returning failure without setting errp).

Opinions and practice vary on this one, and we've discussed the
tradeoffs a few times.

Having both an Error parameter and an error return value poses the
question whether the two agree.  When there's no success value to
transmit, you avoid the problem by making the function return void.  The
problem remains for all the function that return a value on success, and
therefore must return some error value on failure.  A related problem
even remains for functions returning void: consistency between side
effects and the Error parameter.

Returning void leads to awkward boilerplate:

    Error err = NULL;

    foo(..., err);
    if (err) {
        error_propagate(errp, err);
        ... bail out ...
    }

Compare:

    if (!foo(..., errp)) {
        ... bail out ...
    }

Much easier on the eyes.

For what it's worth, GLib wants you to transmit success / failure in the
return value, too:

https://developer.gnome.org/glib/unstable/glib-Error-Reporting.html#gerror-rules

Plenty of older code returns void, some newer code doesn't, because
returning void is just too awkward.  We willfully deviated from GLib's
convention, and we're now paying the price.

See also
Subject: Re: [RFC 00/15] Error API: Flag errors in *errp even if errors are being ignored
Message-ID: <87o9t8qy7d.fsf@dusky.pond.sub.org>
https://lists.gnu.org/archive/html/qemu-devel/2017-06/msg06191.html

> If you really want to do this please use bool as the return type instead
> of int.  int can be abused to return error information that should
> really be in the Error object.

For what it's worth, GLib wants bool[*].  Let's stick to that unless we
have a compelling reason to differ.


[*] Except being GLib, it wants its very own homemade version of bool.
Which is inferior to stdbool.h's in pretty much every conceivable way.

Re: [Qemu-devel] [PATCH 4/6] hw/block: Fix the return type

[Mao Zhongyi]

Hi

On 08/01/2017 10:29 PM, Markus Armbruster wrote:
> Stefan Hajnoczi <stefanha@gmail.com> writes:
>
>> On Wed, Jul 26, 2017 at 08:02:53PM +0800, Mao Zhongyi wrote:
>>> When the function no success value to transmit, it usually make the
>>> function return void. It has turned out not to be a success, because
>>> it means that the extra local_err variable and error_propagate() will
>>> be needed. It leads to cumbersome code, therefore, transmit success/
>>> failure in the return value is worth.
>>>
>>> So fix the return type of blkconf_apply_backend_options(),
>>> blkconf_geometry() and virtio_blk_data_plane_create() to avoid it.
>>>
>>> Cc: John Snow <jsnow@redhat.com>
>>> Cc: Kevin Wolf <kwolf@redhat.com>
>>> Cc: Max Reitz <mreitz@redhat.com>
>>> Cc: Stefan Hajnoczi <stefanha@redhat.com>
>>>
>>> Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
>>> ---
>>>  hw/block/block.c                | 21 ++++++++++++---------
>>>  hw/block/dataplane/virtio-blk.c | 16 +++++++++-------
>>>  hw/block/dataplane/virtio-blk.h |  6 +++---
>>>  include/hw/block/block.h        | 10 +++++-----
>>>  4 files changed, 29 insertions(+), 24 deletions(-)
>>>
>>> diff --git a/hw/block/block.c b/hw/block/block.c
>>> index 27878d0..717bd0e 100644
>>> --- a/hw/block/block.c
>>> +++ b/hw/block/block.c
>>> @@ -51,8 +51,8 @@ void blkconf_blocksizes(BlockConf *conf)
>>>      }
>>>  }
>>>
>>> -void blkconf_apply_backend_options(BlockConf *conf, bool readonly,
>>> -                                   bool resizable, Error **errp)
>>> +int blkconf_apply_backend_options(BlockConf *conf, bool readonly,
>>> +                                  bool resizable, Error **errp)
>>
>> I'm not a fan of these changes because it makes inconsistencies between
>> the return value and the errp argument possible (e.g. returning success
>> but setting errp, or returning failure without setting errp).
>
> Opinions and practice vary on this one, and we've discussed the
> tradeoffs a few times.
>
> Having both an Error parameter and an error return value poses the
> question whether the two agree.  When there's no success value to
> transmit, you avoid the problem by making the function return void.  The
> problem remains for all the function that return a value on success, and
> therefore must return some error value on failure.  A related problem
> even remains for functions returning void: consistency between side
> effects and the Error parameter.
>
> Returning void leads to awkward boilerplate:
>
>     Error err = NULL;
>
>     foo(..., err);
>     if (err) {
>         error_propagate(errp, err);
>         ... bail out ...
>     }
>
> Compare:
>
>     if (!foo(..., errp)) {
>         ... bail out ...
>     }
>
> Much easier on the eyes.
>
> For what it's worth, GLib wants you to transmit success / failure in the
> return value, too:
>
> https://developer.gnome.org/glib/unstable/glib-Error-Reporting.html#gerror-rules
>
> Plenty of older code returns void, some newer code doesn't, because
> returning void is just too awkward.  We willfully deviated from GLib's
> convention, and we're now paying the price.
>
> See also
> Subject: Re: [RFC 00/15] Error API: Flag errors in *errp even if errors are being ignored
> Message-ID: <87o9t8qy7d.fsf@dusky.pond.sub.org>
> https://lists.gnu.org/archive/html/qemu-devel/2017-06/msg06191.html
>
>> If you really want to do this please use bool as the return type instead
>> of int.  int can be abused to return error information that should
>> really be in the Error object.
>
> For what it's worth, GLib wants bool[*].  Let's stick to that unless we
> have a compelling reason to differ.
>
>
> [*] Except being GLib, it wants its very own homemade version of bool.
> Which is inferior to stdbool.h's in pretty much every conceivable way.
>

Thanks for pointing that out！
I will use bool as the return type instead of int.

Thanks,
Mao