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Re: [PATCH for-5.2] spapr: Simplify error handling in spapr_phb_realize(
From: |
Markus Armbruster |
Subject: |
Re: [PATCH for-5.2] spapr: Simplify error handling in spapr_phb_realize() |
Date: |
Mon, 20 Jul 2020 11:29:06 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) |
Greg Kurz <groug@kaod.org> writes:
> The spapr_phb_realize() function has a local_err variable which
> is used to:
>
> 1) check failures of spapr_irq_findone() and spapr_irq_claim()
>
> 2) prepend extra information to the error message
>
> Recent work from Markus Armbruster highlighted we get better
> code when testing the return value of a function, rather than
> setting up all the local_err boiler plate. For similar reasons,
> it is now preferred to use ERRP_GUARD() and error_prepend()
> rather than error_propagate_prepend().
>
> Since spapr_irq_findone() and spapr_irq_claim() return negative
> values in case of failure, do both changes.
>
> This is just cleanup, no functional impact.
>
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
>
> Since we add ERRP_GUARD(), we could theoretically check *errp
> rather than the return value, and thus avoid the uint32_t to
> int32_t change but I personally find it clearer the other way.
> ---
> hw/ppc/spapr_pci.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> index 21681215d405..b1ce51327db4 100644
> --- a/hw/ppc/spapr_pci.c
> +++ b/hw/ppc/spapr_pci.c
> @@ -1796,6 +1796,7 @@ static void spapr_phb_destroy_msi(gpointer opaque)
>
> static void spapr_phb_realize(DeviceState *dev, Error **errp)
> {
> + ERRP_GUARD();
> /* We don't use SPAPR_MACHINE() in order to exit gracefully if the user
> * tries to add a sPAPR PHB to a non-pseries machine.
> */
> @@ -1813,7 +1814,6 @@ static void spapr_phb_realize(DeviceState *dev, Error
> **errp)
> uint64_t msi_window_size = 4096;
> SpaprTceTable *tcet;
> const unsigned windows_supported = spapr_phb_windows_supported(sphb);
> - Error *local_err = NULL;
>
> if (!spapr) {
> error_setg(errp, TYPE_SPAPR_PCI_HOST_BRIDGE " needs a pseries
> machine");
> @@ -1964,13 +1964,12 @@ static void spapr_phb_realize(DeviceState *dev, Error
> **errp)
>
> /* Initialize the LSI table */
> for (i = 0; i < PCI_NUM_PINS; i++) {
> - uint32_t irq = SPAPR_IRQ_PCI_LSI + sphb->index * PCI_NUM_PINS + i;
> + int32_t irq = SPAPR_IRQ_PCI_LSI + sphb->index * PCI_NUM_PINS + i;
(1)
>
> if (smc->legacy_irq_allocation) {
> - irq = spapr_irq_findone(spapr, &local_err);
> - if (local_err) {
> - error_propagate_prepend(errp, local_err,
> - "can't allocate LSIs: ");
> + irq = spapr_irq_findone(spapr, errp);
(2)
> + if (irq < 0) {
> + error_prepend(errp, "can't allocate LSIs: ");
> /*
> * Older machines will never support PHB hotplug, ie, this
> is an
> * init only path and QEMU will terminate. No need to
> rollback.
> @@ -1979,9 +1978,8 @@ static void spapr_phb_realize(DeviceState *dev, Error
> **errp)
> }
> }
>
> - spapr_irq_claim(spapr, irq, true, &local_err);
> - if (local_err) {
> - error_propagate_prepend(errp, local_err, "can't allocate LSIs:
> ");
> + if (spapr_irq_claim(spapr, irq, true, errp) < 0) {
(3)
> + error_prepend(errp, "can't allocate LSIs: ");
> goto unrealize;
> }
sphb->lsi_table[i].irq = irq;
(4)
}
The error propagation elimination looks good to me, but I wonder whether
int32_t is the best choice for @irq.
Before the patch:
(1) The initialization converts unsigned (I think) to uint32_t.
(2) Converts from int (value of spapr_irq_findone()) to uint32_t.
(3) spapr_irq_claim() takes int, we convert back to int.
(4) The assignment does not convert.
After the patch:
(1) The initialization converts unsigned (I think) to int32_t.
(2) Converts from int (value of spapr_irq_findone()) to int32_t.
(3) spapr_irq_claim() takes int, we convert back to int.
(4) Converts from int32_t to uint32_t
I assume the conversions are all safe before and after the patch
(spapr_irq_claim() asserts @irq is between 0x1000 and 0x1000 + small
change). Still, too many conversions for my taste. What about making
irq plain int? Then:
(1) The initialization converts unsigned (I think) to int.
(2) Does not convert.
(3) Does not convert.
(4) Converts from int to uint32_t.
Feels neater to me.
Regardless:
Reviewed-by: Markus Armbruster <armbru@redhat.com>