Re: [Qemu-devel] [PATCH v2 01/35] error: Fix use of error_prepend() with &error_fatal, &error_abort

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 15/10/2018 13:52, Markus Armbruster wrote:
> From include/qapi/error.h:
> 
>   * Pass an existing error to the caller with the message modified:
>   *     error_propagate(errp, err);
>   *     error_prepend(errp, "Could not frobnicate '%s': ", name);
> 
> Fei Li pointed out that doing error_propagate() first doesn't work
> well when @errp is &error_fatal or &error_abort: the error_prepend()
> is never reached.
> 
> Since I doubt fixing the documentation will stop people from getting
> it wrong, introduce error_propagate_prepend(), in the hope that it
> lures people away from using its constituents in the wrong order.
> Update the instructions in error.h accordingly.
> 
> Convert existing error_prepend() next to error_propagate to
> error_propagate_prepend().  If any of these get reached with
> &error_fatal or &error_abort, the error messages improve.  I didn't
> check whether that's the case anywhere.
> 
> Cc: Fei Li <fli@suse.com>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>  block.c                 |  6 +++---
>  block/qcow2.c           |  4 ++--
>  block/qed.c             |  4 ++--
>  hw/9pfs/9p-local.c      |  4 ++--
>  hw/intc/xics.c          | 15 +++++++++------
>  hw/ppc/pnv_core.c       |  4 ++--
>  hw/ppc/spapr_pci.c      |  7 +++----
>  hw/timer/aspeed_timer.c |  3 +--
>  hw/usb/bus.c            |  5 +++--
>  hw/vfio/pci.c           |  3 +--
>  include/qapi/error.h    | 14 ++++++++++++++
>  migration/migration.c   | 12 ++++++------
>  util/error.c            | 13 +++++++++++++
>  13 files changed, 61 insertions(+), 33 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 7710b399a3..5d51419d21 100644
> --- a/block.c
> +++ b/block.c
> @@ -4697,9 +4697,9 @@ bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
>      assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
>      if (!QLIST_EMPTY(&bs->op_blockers[op])) {
>          blocker = QLIST_FIRST(&bs->op_blockers[op]);
> -        error_propagate(errp, error_copy(blocker->reason));
> -        error_prepend(errp, "Node '%s' is busy: ",
> -                      bdrv_get_device_or_node_name(bs));
> +        error_propagate_prepend(errp, error_copy(blocker->reason),
> +                                "Node '%s' is busy: ",
> +                                bdrv_get_device_or_node_name(bs));
>          return true;
>      }
>      return false;
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 7277feda13..4f8d2fa7bd 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2208,8 +2208,8 @@ static void coroutine_fn qcow2_co_invalidate_cache(BlockDriverState *bs,
>      qemu_co_mutex_unlock(&s->lock);
>      qobject_unref(options);
>      if (local_err) {
> -        error_propagate(errp, local_err);
> -        error_prepend(errp, "Could not reopen qcow2 layer: ");
> +        error_propagate_prepend(errp, local_err,
> +                                "Could not reopen qcow2 layer: ");
>          bs->drv = NULL;
>          return;
>      } else if (ret < 0) {
> diff --git a/block/qed.c b/block/qed.c
> index 689ea9d4d5..9377c0b7ad 100644
> --- a/block/qed.c
> +++ b/block/qed.c
> @@ -1606,8 +1606,8 @@ static void coroutine_fn bdrv_qed_co_invalidate_cache(BlockDriverState *bs,
>      ret = bdrv_qed_do_open(bs, NULL, bs->open_flags, &local_err);
>      qemu_co_mutex_unlock(&s->table_lock);
>      if (local_err) {
> -        error_propagate(errp, local_err);
> -        error_prepend(errp, "Could not reopen qed layer: ");
> +        error_propagate_prepend(errp, local_err,
> +                                "Could not reopen qed layer: ");
>          return;
>      } else if (ret < 0) {
>          error_setg_errno(errp, -ret, "Could not reopen qed layer");
> diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
> index c30f4f26bd..08e673a79c 100644
> --- a/hw/9pfs/9p-local.c
> +++ b/hw/9pfs/9p-local.c
> @@ -1509,8 +1509,8 @@ static int local_parse_opts(QemuOpts *opts, FsDriverEntry *fse, Error **errp)
>  
>      fsdev_throttle_parse_opts(opts, &fse->fst, &local_err);
>      if (local_err) {
> -        error_propagate(errp, local_err);
> -        error_prepend(errp, "invalid throttle configuration: ");
> +        error_propagate_prepend(errp, local_err,
> +                                "invalid throttle configuration: ");
>          return -1;
>      }
>  
> diff --git a/hw/intc/xics.c b/hw/intc/xics.c
> index c90c893228..406efee064 100644
> --- a/hw/intc/xics.c
> +++ b/hw/intc/xics.c
> @@ -320,8 +320,9 @@ static void icp_realize(DeviceState *dev, Error **errp)
>  
>      obj = object_property_get_link(OBJECT(dev), ICP_PROP_XICS, &err);
>      if (!obj) {
> -        error_propagate(errp, err);
> -        error_prepend(errp, "required link '" ICP_PROP_XICS "' not found: ");
> +        error_propagate_prepend(errp, err,
> +                                "required link '" ICP_PROP_XICS
> +                                "' not found: ");
>          return;
>      }
>  
> @@ -329,8 +330,9 @@ static void icp_realize(DeviceState *dev, Error **errp)
>  
>      obj = object_property_get_link(OBJECT(dev), ICP_PROP_CPU, &err);
>      if (!obj) {
> -        error_propagate(errp, err);
> -        error_prepend(errp, "required link '" ICP_PROP_CPU "' not found: ");
> +        error_propagate_prepend(errp, err,
> +                                "required link '" ICP_PROP_CPU
> +                                "' not found: ");
>          return;
>      }
>  
> @@ -624,8 +626,9 @@ static void ics_base_realize(DeviceState *dev, Error **errp)
>  
>      obj = object_property_get_link(OBJECT(dev), ICS_PROP_XICS, &err);
>      if (!obj) {
> -        error_propagate(errp, err);
> -        error_prepend(errp, "required link '" ICS_PROP_XICS "' not found: ");
> +        error_propagate_prepend(errp, err,
> +                                "required link '" ICS_PROP_XICS
> +                                "' not found: ");
>          return;
>      }
>      ics->xics = XICS_FABRIC(obj);
> diff --git a/hw/ppc/pnv_core.c b/hw/ppc/pnv_core.c
> index 9750464bf4..ad1bcc7990 100644
> --- a/hw/ppc/pnv_core.c
> +++ b/hw/ppc/pnv_core.c
> @@ -148,8 +148,8 @@ static void pnv_core_realize(DeviceState *dev, Error **errp)
>  
>      chip = object_property_get_link(OBJECT(dev), "chip", &local_err);
>      if (!chip) {
> -        error_propagate(errp, local_err);
> -        error_prepend(errp, "required link 'chip' not found: ");
> +        error_propagate_prepend(errp, local_err,
> +                                "required link 'chip' not found: ");
>          return;
>      }
>  
> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> index c2271e6ed4..58afa46204 100644
> --- a/hw/ppc/spapr_pci.c
> +++ b/hw/ppc/spapr_pci.c
> @@ -1724,16 +1724,15 @@ static void spapr_phb_realize(DeviceState *dev, Error **errp)
>          if (smc->legacy_irq_allocation) {
>              irq = spapr_irq_findone(spapr, &local_err);
>              if (local_err) {
> -                error_propagate(errp, local_err);
> -                error_prepend(errp, "can't allocate LSIs: ");
> +                error_propagate_prepend(errp, local_err,
> +                                        "can't allocate LSIs: ");
>                  return;
>              }
>          }
>  
>          spapr_irq_claim(spapr, irq, true, &local_err);
>          if (local_err) {
> -            error_propagate(errp, local_err);
> -            error_prepend(errp, "can't allocate LSIs: ");
> +            error_propagate_prepend(errp, local_err, "can't allocate LSIs: ");
>              return;
>          }
>  
> diff --git a/hw/timer/aspeed_timer.c b/hw/timer/aspeed_timer.c
> index 54b400b94a..5c786e5128 100644
> --- a/hw/timer/aspeed_timer.c
> +++ b/hw/timer/aspeed_timer.c
> @@ -454,8 +454,7 @@ static void aspeed_timer_realize(DeviceState *dev, Error **errp)
>  
>      obj = object_property_get_link(OBJECT(dev), "scu", &err);
>      if (!obj) {
> -        error_propagate(errp, err);
> -        error_prepend(errp, "required link 'scu' not found: ");
> +        error_propagate_prepend(errp, err, "required link 'scu' not found: ");
>          return;
>      }
>      s->scu = ASPEED_SCU(obj);
> diff --git a/hw/usb/bus.c b/hw/usb/bus.c
> index 11f7720d71..bf796d67e6 100644
> --- a/hw/usb/bus.c
> +++ b/hw/usb/bus.c
> @@ -340,8 +340,9 @@ static USBDevice *usb_try_create_simple(USBBus *bus, const char *name,
>      }
>      object_property_set_bool(OBJECT(dev), true, "realized", &err);
>      if (err) {
> -        error_propagate(errp, err);
> -        error_prepend(errp, "Failed to initialize USB device '%s': ", name);
> +        error_propagate_prepend(errp, err,
> +                                "Failed to initialize USB device '%s': ",
> +                                name);
>          return NULL;
>      }
>      return dev;
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 866f0deeb7..8c95fc648a 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -1280,8 +1280,7 @@ static int vfio_msi_setup(VFIOPCIDevice *vdev, int pos, Error **errp)
>          if (ret == -ENOTSUP) {
>              return 0;
>          }
> -        error_prepend(&err, "msi_init failed: ");
> -        error_propagate(errp, err);
> +        error_propagate_prepend(errp, err, "msi_init failed: ");
>          return ret;
>      }
>      vdev->msi_cap_size = 0xa + (msi_maskbit ? 0xa : 0) + (msi_64bit ? 0x4 : 0);
> diff --git a/include/qapi/error.h b/include/qapi/error.h
> index bcb86a79f5..51b63dd4b5 100644
> --- a/include/qapi/error.h
> +++ b/include/qapi/error.h
> @@ -52,8 +52,12 @@
>   * where Error **errp is a parameter, by convention the last one.
>   *
>   * Pass an existing error to the caller with the message modified:
> + *     error_propagate_prepend(errp, err);
> + *
> + * Avoid
>   *     error_propagate(errp, err);
>   *     error_prepend(errp, "Could not frobnicate '%s': ", name);
> + * because this fails to prepend when @errp is &error_fatal.
>   *
>   * Create a new error and pass it to the caller:
>   *     error_setg(errp, "situation normal, all fouled up");
> @@ -215,6 +219,16 @@ void error_setg_win32_internal(Error **errp,
>   */
>  void error_propagate(Error **dst_errp, Error *local_err);
>  
> +
> +/*
> + * Propagate error object (if any) with some text prepended.
> + * Behaves like
> + *     error_prepend(&local_err, fmt, ...);
> + *     error_propagate(dst_errp, local_err);
> + */
> +void error_propagate_prepend(Error **dst_errp, Error *local_err,
> +                             const char *fmt, ...);
> +
>  /*
>   * Prepend some text to @errp's human-readable error message.
>   * The text is made by formatting @fmt, @ap like vprintf().
> diff --git a/migration/migration.c b/migration/migration.c
> index d6ae879dc8..f0f299a773 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1546,9 +1546,9 @@ static GSList *migration_blockers;
>  int migrate_add_blocker(Error *reason, Error **errp)
>  {
>      if (migrate_get_current()->only_migratable) {
> -        error_propagate(errp, error_copy(reason));
> -        error_prepend(errp, "disallowing migration blocker "
> -                          "(--only_migratable) for: ");
> +        error_propagate_prepend(errp, error_copy(reason),
> +                                "disallowing migration blocker "
> +                                "(--only_migratable) for: ");
>          return -EACCES;
>      }
>  
> @@ -1557,9 +1557,9 @@ int migrate_add_blocker(Error *reason, Error **errp)
>          return 0;
>      }
>  
> -    error_propagate(errp, error_copy(reason));
> -    error_prepend(errp, "disallowing migration blocker (migration in "
> -                      "progress) for: ");
> +    error_propagate_prepend(errp, error_copy(reason),
> +                            "disallowing migration blocker "
> +                            "(migration in progress) for: ");
>      return -EBUSY;
>  }
>  
> diff --git a/util/error.c b/util/error.c
> index 3efdd69162..b5ccbd8eac 100644
> --- a/util/error.c
> +++ b/util/error.c
> @@ -292,3 +292,16 @@ void error_propagate(Error **dst_errp, Error *local_err)
>          error_free(local_err);
>      }
>  }
> +
> +void error_propagate_prepend(Error **dst_errp, Error *err,
> +                             const char *fmt, ...)
> +{
> +    va_list ap;
> +
> +    if (dst_errp && !*dst_errp) {
> +        va_start(ap, fmt);
> +        error_vprepend(&err, fmt, ap);
> +        va_end(ap);
> +    } /* else error is being ignored, don't bother with prepending */
> +    error_propagate(dst_errp, err);
> +}
> 

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>