Re: [PATCH v3] mm/page_owner.c: add llseek for page_owner

[Kassey Li <quic_yingangl@quicinc.com>]

On 7/30/2022 10:28 AM, Souptick Joarder wrote:
> On Fri, Jul 29, 2022 at 6:19 AM Kassey Li <quic_yingangl@quicinc.com> wrote:
>>
>> There is usage to dump a given cma region page_owner
>> instead of all page's.
>>
>> This change allows to specify a ppos as start_pfn
>> by fseek.
>>
>> Any invalid ppos will be skipped, so it did not
>> broken the origin dump feature.
>>
> 
> I think a Suggested-by tag needs to be added.
   re-send it again. please help to review, thanks.
> 
> 
>> Signed-off-by: Kassey Li <quic_yingangl@quicinc.com>
>> ---
>>   mm/page_owner.c | 20 ++++++++++++++++++--
>>   1 file changed, 18 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/page_owner.c b/mm/page_owner.c
>> index e4c6f3f1695b..231b1877af99 100644
>> --- a/mm/page_owner.c
>> +++ b/mm/page_owner.c
>> @@ -497,8 +497,8 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>>                  return -EINVAL;
>>
>>          page = NULL;
>> -       pfn = min_low_pfn + *ppos;
>>
>> +       pfn = *ppos;
>>          /* Find a valid PFN or the start of a MAX_ORDER_NR_PAGES area */
>>          while (!pfn_valid(pfn) && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0)
>>                  pfn++;
>> @@ -561,7 +561,7 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>>                          continue;
>>
>>                  /* Record the next PFN to read in the file offset */
>> -               *ppos = (pfn - min_low_pfn) + 1;
>> +               *ppos = pfn + 1;
>>
>>                  return print_page_owner(buf, count, pfn, page,
>>                                  page_owner, handle);
>> @@ -570,6 +570,21 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>>          return 0;
>>   }
>>
>> +static loff_t llseek_page_owner(struct file *file, loff_t offset, int whence)
>> +{
>> +       loff_t retval = 0;
>> +       switch (whence) {
>> +               case SEEK_CUR:
>> +               case SEEK_SET:
>> +                       file->f_pos = offset;
>> +                       break;
>> +               default:
>> +                       retval = -ENXIO;
>> +       }
>> +
>> +       return retval;
>> +}
>> +
>>   static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone)
>>   {
>>          unsigned long pfn = zone->zone_start_pfn;
>> @@ -660,6 +675,7 @@ static void init_early_allocated_pages(void)
>>
>>   static const struct file_operations proc_page_owner_operations = {
>>          .read           = read_page_owner,
>> +       .llseek         = llseek_page_owner,
>>   };
>>
>>   static int __init pageowner_init(void)
>> --
>> 2.17.1
>>
>>