Re: [PATCH v16 net-next 1/9] octeontx2-af: npc: cn20k: debugfs enhancements

[Ratheesh Kannoth <rkannoth@marvell.com>]

On 2026-05-21 at 15:22:55, Ratheesh Kannoth (rkannoth@marvell.com) wrote:
> Improve MCAM visibility and field debugging for CN20K NPC.

[ ... ]
>> +#define DEFINE_OCTEONTX2_DEBUGFS_ATTRIBUTE_WITH_SIZE(__name, __size)		\
>> +static int __name ## _open(struct inode *inode, struct file *file)		\
>> +{										\
>> +	return single_open_size(file, __name ## _show, inode->i_private,	\
>> +				__size);					\
>> +}										\
>> +__OCTEONTX2_DEBUGFS_ATTRIBUTE_FOPS(__name)
>[ ... ]
>> +			delta = stats - dstats[bank][idx];
>> +
>> +			snprintf(buff, sizeof(buff), "%u\t%#04x\t%llu\n",
>> +				 mcam_idx, pf, delta);
>> +			seq_puts(s, buff);
>> +
>> +			dstats[bank][idx] = stats;
>> +		}
>> +	}
>> +
>> +	mutex_unlock(&stats_lock);
>> +	return 0;
>> +}
>> +
 +
>> +/*  "%u\t%#04x\t%llu\n" needs less than 64 characters to print */
>> +#define TOTAL_SZ (MAX_NUM_BANKS * MAX_NUM_SUB_BANKS * MAX_SUBBANK_DEPTH * 64)
>> +DEFINE_OCTEONTX2_DEBUGFS_ATTRIBUTE_WITH_SIZE(npc_mcam_dstats, TOTAL_SZ);
>Does this code use single_open_size() to force a 1MB allocation to avoid
>seq_file buffer overflow?
>For dstats, the show function modifies state by updating dstats[bank][idx].
>If the seq_file buffer were to overflow and restart, it would skip entries
>or report zero deltas. Bypassing the seq_file dynamic resizing with a 1MB
>upfront allocation per file open wastes memory to hide a seq_file idempotency
>issue.
>>
if i understand it correctly, seq_file idempotency issue occurs only if .next() function
is a custom implementation. In our case, we are not using custom .next() function, so it wont
happen in this case.