On 07/22/2016 11:56 PM, Ewan D. Milne wrote:
> On Tue, 2016-07-19 at 15:25 +0200, Hannes Reinecke wrote:
>> For ZBC devices I/O must not cross zone boundaries, so setup
>> the 'chunk_sectors' block queue setting to the zone size.
>> This is only valid for REPORT ZONES SAME type 2 or 3;
>> for other types the zone sizes might be different
>> for individual zones. So issue a warning if the type is
>> found to be different.
>> Also the capacity might be different from the announced
>> capacity, so adjust it as needed.
>>
>> Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
>
> ...
>
>> +static void sd_read_zones(struct scsi_disk *sdkp, unsigned char *buffer)
>> +{
>> + int retval;
>> + unsigned char *desc;
>> + u32 rep_len;
>> + u8 same;
>> + u64 zone_len, lba;
>> +
>> + if (sdkp->zoned != 1)
>> + /* Device managed, no special handling required */
>> + return;
>> +
>> + retval = sd_zbc_report_zones(sdkp, buffer, SD_BUF_SIZE,
>> + 0, ZBC_ZONE_REPORTING_OPTION_ALL, false);
>> + if (retval < 0)
>> + return;
>> +
>> + rep_len = get_unaligned_be32(&buffer[0]);
>> + if (rep_len < 64) {
>> + sd_printk(KERN_WARNING, sdkp,
>> + "REPORT ZONES report invalid length %u\n",
>> + rep_len);
>> + return;
>> + }
>> +
>> + if (sdkp->rc_basis == 0) {
>> + /* The max_lba field is the capacity of a zoned device */
>> + lba = get_unaligned_be64(&buffer[8]);
>> + if (lba + 1 > sdkp->capacity) {
>> + sd_printk(KERN_WARNING, sdkp,
>> + "Max LBA %zu (capacity %zu)\n",
>> + (sector_t) lba + 1, sdkp->capacity);
>> + sdkp->capacity = lba + 1;
>> + }
>> + }
>> +
>> + /*
>> + * Adjust 'chunk_sectors' to the zone length if the device
>> + * supports equal zone sizes.
>> + */
>> + same = buffer[4] & 0xf;
>> + if (same == 0 || same > 3) {
>> + sd_printk(KERN_WARNING, sdkp,
>> + "REPORT ZONES SAME type %d not supported\n", same);
>> + return;
>> + }
>> + /* Read the zone length from the first zone descriptor */
>> + desc = &buffer[64];
>> + zone_len = logical_to_sectors(sdkp->device,
>> + get_unaligned_be64(&desc[8]));
>> + blk_queue_chunk_sectors(sdkp->disk->queue, zone_len);
>> +}
>> +
>
> So, blk_queue_chunk_sectors() has:
>
> void blk_queue_chunk_sectors(struct request_queue *q, unsigned int chunk_sectors)
> {
> BUG_ON(!is_power_of_2(chunk_sectors));
> q->limits.chunk_sectors = chunk_sectors;
> }
>
> and it seems like if some device reports a non-power-of-2 zone_len then we
> will BUG_ON(). Probably would be better if we reported an error instead?
>
The ZBC spec mandates that the zone size must be a power of 2.
So I don't have problems with triggering a BUG_ON for non-compliant
drives.
Cheers,
Hannes
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