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

[Markus Armbruster]

Thomas Huth <address@hidden> writes:

> 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 <address@hidden>
>> ---
>>  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)

Good point.

With abort() / exit(), we don't have to worry about recovery.  In
particular, we don't have to revert half-done changes.

Conversions away from abort() / exit() need to consider error recovery.
We have to make sure the function leaves things in a sane state on
error.  This normally means taking an early return, and often means
reverting some state changes.

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