Re: [Qemu-devel] [PATCHv3 3/9] pseries: Clean up hash page table allocation error handling

[Thomas Huth <thuth@redhat.com>]

On 18.01.2016 05:24, David Gibson wrote:
> The spapr_alloc_htab() and spapr_reset_htab() functions currently handle
> all errors with error_setg(&error_abort, ...).
> 
> But really, the callers are really better placed to decide on the error
> handling.  So, instead make the functions use the error propagation
> infrastructure.
> 
> In the callers we change to &error_fatal instead of &error_abort, since
> this can be triggered by a bad configuration or kernel error rather than
> indicating a programming error in qemu.
> 
> While we're at it improve the messages themselves a bit, and clean up the
> indentation a little.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  hw/ppc/spapr.c | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index b7fd09a..d28e349 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1016,7 +1016,7 @@ static void emulate_spapr_hypercall(PowerPCCPU *cpu)
>  #define CLEAN_HPTE(_hpte)  ((*(uint64_t *)(_hpte)) &= tswap64(~HPTE64_V_HPTE_DIRTY))
>  #define DIRTY_HPTE(_hpte)  ((*(uint64_t *)(_hpte)) |= tswap64(HPTE64_V_HPTE_DIRTY))
>  
> -static void spapr_alloc_htab(sPAPRMachineState *spapr)
> +static void spapr_alloc_htab(sPAPRMachineState *spapr, Error **errp)
>  {
>      long shift;
>      int index;
> @@ -1031,7 +1031,8 @@ static void spapr_alloc_htab(sPAPRMachineState *spapr)
>           * For HV KVM, host kernel will return -ENOMEM when requested
>           * HTAB size can't be allocated.
>           */
> -        error_setg(&error_abort, "Failed to allocate HTAB of requested size, try with smaller maxmem");
> +        error_setg_errno(errp, -shift,
> +                         "Error allocating KVM hash page table, try smaller maxmem");
>      } else if (shift > 0) {
>          /*
>           * Kernel handles htab, we don't need to allocate one
> @@ -1040,7 +1041,10 @@ static void spapr_alloc_htab(sPAPRMachineState *spapr)
>           * but we don't allow booting of such guests.
>           */
>          if (shift != spapr->htab_shift) {
> -            error_setg(&error_abort, "Failed to allocate HTAB of requested size, try with smaller maxmem");
> +            error_setg(errp,
> +                "Small allocation for KVM hash page table (%ld < %"
> +                PRIu32 "), try smaller maxmem",
> +                shift, spapr->htab_shift);

Maybe you should add an "return" statement here - theoretically you do
not want to continue with "kvmppc_kern_htab = true" in case of errors.
(practically this does not happen because errp = error_fatal, but in
case the caller gets changed, this might introduce subtle errors otherwise)

>          }
>  
>          spapr->htab_shift = shift;
> @@ -1064,17 +1068,21 @@ static void spapr_alloc_htab(sPAPRMachineState *spapr)
>   * If host kernel has allocated HTAB, KVM_PPC_ALLOCATE_HTAB ioctl is
>   * used to clear HTAB. Otherwise QEMU-allocated HTAB is cleared manually.
>   */
> -static void spapr_reset_htab(sPAPRMachineState *spapr)
> +static void spapr_reset_htab(sPAPRMachineState *spapr, Error **errp)
>  {
>      long shift;
>      int index;
>  
>      shift = kvmppc_reset_htab(spapr->htab_shift);
>      if (shift < 0) {
> -        error_setg(&error_abort, "Failed to reset HTAB");
> +        error_setg_errno(errp, -shift,
> +                   "Error resetting KVM hash page table, try smaller maxmem");

dito, better do an "return" here...

>      } else if (shift > 0) {
>          if (shift != spapr->htab_shift) {
> -            error_setg(&error_abort, "Requested HTAB allocation failed during reset");
> +            error_setg(errp,
> +                "Reduced size on reset of KVM hash page table (%ld < %"
> +                PRIu32 "), try smaller maxmem",
> +                shift, spapr->htab_shift);

... and here.

>          }
>  
>          /* Tell readers to update their file descriptor */
> @@ -1145,7 +1153,7 @@ static void ppc_spapr_reset(void)
>      foreach_dynamic_sysbus_device(find_unknown_sysbus_device, NULL);
>  
>      /* Reset the hash table & recalc the RMA */
> -    spapr_reset_htab(spapr);
> +    spapr_reset_htab(spapr, &error_fatal);
>  
>      qemu_devices_reset();
>  
> @@ -1792,7 +1800,7 @@ static void ppc_spapr_init(MachineState *machine)
>          }
>          spapr->htab_shift++;
>      }
> -    spapr_alloc_htab(spapr);
> +    spapr_alloc_htab(spapr, &error_fatal);
>  
>      /* Set up Interrupt Controller before we create the VCPUs */
>      spapr->icp = xics_system_init(machine,
> 

 Thomas