Sorry, "redundant check" is not the best word to describe this patch. The result of this patch is that: 1. if opt_xfer_blocks has a valid value (returned form VPD BLOCK LIMITS), use it to set max_sectors 2. if opt_xfer_blocks doesn't have a valid value, leave max_sectors unchanged The reason is that, max_sectors already has value at this point, the default value is SCSI_DEFAULT_MAX_SECTORS (include/scsi/scsi_host.h). The lower layer host driver can change this value in its template. I think the drivers care about this value have already set it. So it's better not to change it again. If they want max_sectors to be set by sd, they can use BLOCK LIMITS VPD to tell it to do so. > -----Original Message----- > From: Tom Yan [mailto:tom.ty89@xxxxxxxxx] > Sent: Saturday, June 4, 2016 1:41 AM > To: Long Li <longli@xxxxxxxxxxxxx> > Cc: James E.J. Bottomley <jejb@xxxxxxxxxxxxxxxxxx>; Martin K. Petersen > <martin.petersen@xxxxxxxxxx>; linux-scsi@xxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH] sd: remove redundant check for > BLK_DEF_MAX_SECTORS > > The main point there is not to check q->limits.max_sectors against > BLK_DEF_MAX_SECTORS, but sdkp->opt_xfer_blocks against > SD_DEF_XFER_BLOCKS et al.? `rw_max = BLK_DEF_MAX_SECTORS;` there is > merely the fallback when sdkp->opt_xfer_blocks does not pass the > conditions. With your patch `rw_max` can be indeterminate in those > circumstances. > > On 4 June 2016 at 11:57, Long Li <longli@xxxxxxxxxxxxx> wrote: > > q->limits.max_sectors is already checked against BLK_DEF_MAX_SECTORS > in __scsi_alloc_queue(), when it calls blk_queue_max_hw_sectors(). There > is no need to check it again in sd. > > > > This change also allows a SCSI driver set an maximum sector size bigger > than BLK_DEF_MAX_SECTORS, without returning values on optional VPD > page 0xb0 "Block Limits". > > > > Signed-off-by: Long Li <longli@xxxxxxxxxxxxx> > > > > --- > > drivers/scsi/sd.c | 7 ++----- > > 1 file changed, 2 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index > > 60bff78..d8c4047 100644 > > --- a/drivers/scsi/sd.c > > +++ b/drivers/scsi/sd.c > > @@ -2870,11 +2870,8 @@ static int sd_revalidate_disk(struct gendisk *disk) > > logical_to_bytes(sdp, sdkp->opt_xfer_blocks) >= PAGE_SIZE) { > > q->limits.io_opt = logical_to_bytes(sdp, sdkp->opt_xfer_blocks); > > rw_max = logical_to_sectors(sdp, sdkp->opt_xfer_blocks); > > - } else > > - rw_max = BLK_DEF_MAX_SECTORS; > > - > > - /* Combine with controller limits */ > > - q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q)); > > + q->limits.max_sectors = min(rw_max, > queue_max_hw_sectors(q)); > > + } > > > > set_capacity(disk, logical_to_sectors(sdp, sdkp->capacity)); > > sd_config_write_same(sdkp); > > -- > > 2.7.4 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-scsi" > > in the body of a message to majordomo@xxxxxxxxxxxxxxx More > majordomo > > info at > > https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fvger.k > > ernel.org%2fmajordomo- > info.html&data=01%7c01%7clongli%40microsoft.com% > > > 7ce142128958ec47629dbe08d38c540306%7c72f988bf86f141af91ab2d7cd011d > b47% > > 7c1&sdata=EjjF86cvJqaxOAOWnN0%2f3Qln05qcquwe%2fKA7DgEjtcI%3d ��.n��������+%������w��{.n�����{������ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
