[RFC PATCH-for-5.2 v2 2/2] block/block-backend: Let blk_attach_dev() provide helpful error

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

Let blk_attach_dev() take an Error* object to return helpful
information. Adapt the callers.

  $ qemu-system-arm -M n800
  qemu-system-arm: sd_init failed: cannot attach blk 'sd0' to device 'sd-card'
  blk 'sd0' is already attached by device 'omap2-mmc'
  Drive 'sd0' is already in use because it has been automatically connected to another device
  (do you need 'if=none' in the drive options?)

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
v2: Rebased after 668f62ec62 ("error: Eliminate error_propagate()")
---
 include/sysemu/block-backend.h   |  2 +-
 block/block-backend.c            | 11 ++++++++++-
 hw/block/fdc.c                   |  4 +---
 hw/block/swim.c                  |  4 +---
 hw/block/xen-block.c             |  5 +++--
 hw/core/qdev-properties-system.c | 16 +++++++++-------
 hw/ide/qdev.c                    |  4 +---
 hw/scsi/scsi-disk.c              |  4 +---
 8 files changed, 27 insertions(+), 23 deletions(-)

diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 8203d7f6f9..118fbad0b4 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -113,7 +113,7 @@ BlockDeviceIoStatus blk_iostatus(const BlockBackend *blk);
 void blk_iostatus_disable(BlockBackend *blk);
 void blk_iostatus_reset(BlockBackend *blk);
 void blk_iostatus_set_err(BlockBackend *blk, int error);
-int blk_attach_dev(BlockBackend *blk, DeviceState *dev);
+int blk_attach_dev(BlockBackend *blk, DeviceState *dev, Error **errp);
 void blk_detach_dev(BlockBackend *blk, DeviceState *dev);
 DeviceState *blk_get_attached_dev(BlockBackend *blk);
 char *blk_get_attached_dev_id(BlockBackend *blk);
diff --git a/block/block-backend.c b/block/block-backend.c
index 63ff940ef9..b7be0a4619 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -884,12 +884,21 @@ void blk_get_perm(BlockBackend *blk, uint64_t *perm, uint64_t *shared_perm)
 
 /*
  * Attach device model @dev to @blk.
+ *
+ * @blk: Block backend
+ * @dev: Device to attach the block backend to
+ * @errp: pointer to NULL initialized error object
+ *
  * Return 0 on success, -EBUSY when a device model is attached already.
  */
-int blk_attach_dev(BlockBackend *blk, DeviceState *dev)
+int blk_attach_dev(BlockBackend *blk, DeviceState *dev, Error **errp)
 {
     trace_blk_attach_dev(blk_name(blk), object_get_typename(OBJECT(dev)));
     if (blk->dev) {
+        error_setg(errp, "cannot attach blk '%s' to device '%s'",
+                   blk_name(blk), object_get_typename(OBJECT(dev)));
+        error_append_hint(errp, "blk '%s' is already attached by device '%s'\n",
+                          blk_name(blk), object_get_typename(OBJECT(blk->dev)));
         return -EBUSY;
     }
 
diff --git a/hw/block/fdc.c b/hw/block/fdc.c
index e9ed3eef45..bc39244152 100644
--- a/hw/block/fdc.c
+++ b/hw/block/fdc.c
@@ -519,7 +519,6 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp)
     FloppyBus *bus = FLOPPY_BUS(qdev->parent_bus);
     FDrive *drive;
     bool read_only;
-    int ret;
 
     if (dev->unit == -1) {
         for (dev->unit = 0; dev->unit < MAX_FD; dev->unit++) {
@@ -545,8 +544,7 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp)
     if (!dev->conf.blk) {
         /* Anonymous BlockBackend for an empty drive */
         dev->conf.blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL);
-        ret = blk_attach_dev(dev->conf.blk, qdev);
-        assert(ret == 0);
+        blk_attach_dev(dev->conf.blk, qdev, &error_abort);
 
         /* Don't take write permissions on an empty drive to allow attaching a
          * read-only node later */
diff --git a/hw/block/swim.c b/hw/block/swim.c
index 74f56e8f46..2f1ecd0bb2 100644
--- a/hw/block/swim.c
+++ b/hw/block/swim.c
@@ -159,7 +159,6 @@ static void swim_drive_realize(DeviceState *qdev, Error **errp)
     SWIMDrive *dev = SWIM_DRIVE(qdev);
     SWIMBus *bus = SWIM_BUS(qdev->parent_bus);
     FDrive *drive;
-    int ret;
 
     if (dev->unit == -1) {
         for (dev->unit = 0; dev->unit < SWIM_MAX_FD; dev->unit++) {
@@ -185,8 +184,7 @@ static void swim_drive_realize(DeviceState *qdev, Error **errp)
     if (!dev->conf.blk) {
         /* Anonymous BlockBackend for an empty drive */
         dev->conf.blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL);
-        ret = blk_attach_dev(dev->conf.blk, qdev);
-        assert(ret == 0);
+        blk_attach_dev(dev->conf.blk, qdev, &error_abort);
     }
 
     if (!blkconf_blocksizes(&dev->conf, errp)) {
diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index 8a7a3f5452..eb99757faf 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -609,14 +609,15 @@ static void xen_cdrom_realize(XenBlockDevice *blockdev, Error **errp)
     blockdev->device_type = "cdrom";
 
     if (!conf->blk) {
+        Error *local_err = NULL;
         int rc;
 
         /* Set up an empty drive */
         conf->blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL);
 
-        rc = blk_attach_dev(conf->blk, DEVICE(blockdev));
+        rc = blk_attach_dev(conf->blk, DEVICE(blockdev), &local_err);
         if (!rc) {
-            error_setg_errno(errp, -rc, "failed to create drive");
+            error_propagate_prepend(errp, local_err, "failed to create drive");
             return;
         }
     }
diff --git a/hw/core/qdev-properties-system.c b/hw/core/qdev-properties-system.c
index 3e4f16fc21..e3a757b1c3 100644
--- a/hw/core/qdev-properties-system.c
+++ b/hw/core/qdev-properties-system.c
@@ -136,17 +136,19 @@ static void set_drive_helper(Object *obj, Visitor *v, const char *name,
                    object_get_typename(OBJECT(dev)), prop->name, str);
         goto fail;
     }
-    if (blk_attach_dev(blk, dev) < 0) {
+    if (blk_attach_dev(blk, dev, errp) < 0) {
         DriveInfo *dinfo = blk_legacy_dinfo(blk);
 
         if (dinfo && dinfo->type != IF_NONE) {
-            error_setg(errp, "Drive '%s' is already in use because "
-                       "it has been automatically connected to another "
-                       "device (did you need 'if=none' in the drive options?)",
-                       str);
+            error_append_hint(errp,
+                              "Drive '%s' is already in use because it has "
+                              "been automatically connected to another device\n"
+                              "(do you need 'if=none' in the drive options?)\n",
+                              str);
         } else {
-            error_setg(errp, "Drive '%s' is already in use by another device",
-                       str);
+            error_append_hint(errp,
+                              "Drive '%s' is already in use by another device",
+                              str);
         }
         goto fail;
     }
diff --git a/hw/ide/qdev.c b/hw/ide/qdev.c
index 27ff1f7f66..9a02eb87f4 100644
--- a/hw/ide/qdev.c
+++ b/hw/ide/qdev.c
@@ -165,7 +165,6 @@ 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;
-    int ret;
 
     if (!dev->conf.blk) {
         if (kind != IDE_CD) {
@@ -174,8 +173,7 @@ static void ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind, Error **errp)
         } else {
             /* Anonymous BlockBackend for an empty drive */
             dev->conf.blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL);
-            ret = blk_attach_dev(dev->conf.blk, &dev->qdev);
-            assert(ret == 0);
+            blk_attach_dev(dev->conf.blk, &dev->qdev, &error_abort);
         }
     }
 
diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index 8ce68a9dd6..92350642c7 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -2451,14 +2451,12 @@ static void scsi_cd_realize(SCSIDevice *dev, Error **errp)
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, dev);
     AioContext *ctx;
-    int ret;
 
     if (!dev->conf.blk) {
         /* Anonymous BlockBackend for an empty drive. As we put it into
          * dev->conf, qdev takes care of detaching on unplug. */
         dev->conf.blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL);
-        ret = blk_attach_dev(dev->conf.blk, &dev->qdev);
-        assert(ret == 0);
+        blk_attach_dev(dev->conf.blk, &dev->qdev, &error_abort);
     }
 
     ctx = blk_get_aio_context(dev->conf.blk);
-- 
2.21.3