[PATCH] sd: preserve sysfs updates to max_sectors_kb

[Don Brace]

prevent systemd-udevd from changing a device's sysfs entry
max_sectors_kb back to the default value.
 - max_sectors_kb can be tweaked for better performance.
 - udev can be triggered by sg_logs -t or scsi_temperature, ...
 - sd_revalidate_disk is called from udev by ioctl BLKRRPART

Reviewed-by: Scott Teel <scott.t...@microsemi.com>
Signed-off-by: Don Brace <don.br...@microsemi.com>
---
 drivers/scsi/sd.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index bea36ad..457dc7c 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3055,6 +3055,7 @@ static int sd_revalidate_disk(struct gendisk *disk)
        sector_t old_capacity = sdkp->capacity;
        unsigned char *buffer;
        unsigned int dev_max, rw_max;
+       unsigned int max_sectors;
 
        SCSI_LOG_HLQUEUE(3, sd_printk(KERN_INFO, sdkp,
                                      "sd_revalidate_disk\n"));
@@ -3128,9 +3129,14 @@ static int sd_revalidate_disk(struct gendisk *disk)
                rw_max = min_not_zero(logical_to_sectors(sdp, dev_max),
                                      (sector_t)BLK_DEF_MAX_SECTORS);
 
-       /* Combine with controller limits */
-       q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q));
+       /* Check for max_sectors_kb update through sysfs */
+       if (q->limits.max_sectors < min(rw_max, queue_max_hw_sectors(q)))
+               max_sectors = q->limits.max_sectors;
+       else
+               max_sectors = min(rw_max, queue_max_hw_sectors(q));
 
+       /* Combine with controller limits */
+       q->limits.max_sectors = max_sectors;
        set_capacity(disk, logical_to_sectors(sdp, sdkp->capacity));
        sd_config_write_same(sdkp);
        kfree(buffer);