Re: [PATCH 1/2] dump: simplify a bit kdump get_next_page()

[David Hildenbrand]

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) {" ? :)

> +        *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.

-- 
Thanks,

David / dhildenb