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Re: [PATCH 1/2] dump: simplify a bit kdump get_next_page()
From: |
David Hildenbrand |
Subject: |
Re: [PATCH 1/2] dump: simplify a bit kdump get_next_page() |
Date: |
Fri, 26 Aug 2022 11:58:17 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 |
On 26.08.22 11:56, Marc-André Lureau wrote:
> Hi
>
> On Fri, Aug 26, 2022 at 1:45 PM David Hildenbrand <david@redhat.com> wrote:
>>
>> On 25.08.22 15:21, marcandre.lureau@redhat.com wrote:
>>> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>>>
>>> This should be functionally equivalent, but slightly easier to read,
>>> with simplified paths and checks at the end of the function.
>>>
>>> The following patch is a major rewrite to get rid of the assert().
>>>
>>> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>>> ---
>>> dump/dump.c | 30 ++++++++++++------------------
>>> 1 file changed, 12 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/dump/dump.c b/dump/dump.c
>>> index 4d9658ffa2..18f06cffe2 100644
>>> --- a/dump/dump.c
>>> +++ b/dump/dump.c
>>> @@ -1107,37 +1107,31 @@ static bool get_next_page(GuestPhysBlock
>>> **blockptr, uint64_t *pfnptr,
>>> uint8_t *buf;
>>>
>>> /* block == NULL means the start of the iteration */
>>> - if (!block) {
>>> - block = QTAILQ_FIRST(&s->guest_phys_blocks.head);
>>> - *blockptr = block;
>>> - assert((block->target_start & ~target_page_mask) == 0);
>>> - assert((block->target_end & ~target_page_mask) == 0);
>>> - *pfnptr = dump_paddr_to_pfn(s, block->target_start);
>>> - if (bufptr) {
>>> - *bufptr = block->host_addr;
>>> - }
>>> - return true;
>>
>>
>> Instead of the "return true" we'll now do take the "if ((addr >=
>> block->target_start) &&" path below I guess, always ending up with
>> essentially "buf = buf;" because addr == block->target_start.
>>
>> I guess that's fine.
>>
>>> + if (block == NULL) {
>>
>> What's wrong with keeping the "if (!block) {" ? :)
>
> That's just to be consistent with the comment above.
>
>>
>>> + *blockptr = block = QTAILQ_FIRST(&s->guest_phys_blocks.head);
>>
>> Another unnecessary change.
>>
>>> + addr = block->target_start;
>>> + } else {
>>> + addr = dump_pfn_to_paddr(s, *pfnptr + 1);
>>> }
>>> -
>>> - *pfnptr = *pfnptr + 1;
>>> - addr = dump_pfn_to_paddr(s, *pfnptr);
>>> + assert(block != NULL);
>>>
>>> if ((addr >= block->target_start) &&
>>> (addr + s->dump_info.page_size <= block->target_end)) {
>>> buf = block->host_addr + (addr - block->target_start);
>>> } else {
>>> /* the next page is in the next block */
>>> - block = QTAILQ_NEXT(block, next);
>>> - *blockptr = block;
>>> + *blockptr = block = QTAILQ_NEXT(block, next);
>>
>> Another unnecessary change. (avoiding these really eases review, because
>> the focus is then completely on the actual code changes)
>>
>>> if (!block) {
>>> return false;
>>> }
>>> - assert((block->target_start & ~target_page_mask) == 0);
>>> - assert((block->target_end & ~target_page_mask) == 0);
>>> - *pfnptr = dump_paddr_to_pfn(s, block->target_start);
>>> + addr = block->target_start;
>>> buf = block->host_addr;
>>> }
>>>
>>> + /* those checks are going away next */
>>
>> This comment seems to imply a story documented in code. Rather just drop
>> it -- the patch description already points that out.
>>
>>> + assert((block->target_start & ~target_page_mask) == 0);
>>> + assert((block->target_end & ~target_page_mask) == 0);
>>> + *pfnptr = dump_paddr_to_pfn(s, addr);
>>> if (bufptr) {
>>> *bufptr = buf;
>>> }
>>
>>
>> Apart from the nits, LGTM.
>
> We could also drop this patch, it helped me to rewrite the function next
> mostly.
I think it's fine. Small logical changes are easier to review -- at
least for me.
--
Thanks,
David / dhildenb