On Mon, Feb 22, 2010 at 11:14 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
Dear Alan,
Thanks for the information.
> Usb-storage sets max_sectors to 240 in the host template. For some
> reason, the block layer also changes max_hw_sectors to the same value
> (see block/blk-settings.c:blk_queue_max_sectors()).
I am setting the max_sectors in host template (scsiglue.c file). When
the max_sectors value is <= 1024, then only the max_sectors_kb and
max_hw_sectors_kb are same in the sys interface. However, if the
max_sectors value is > 1024 then the values in the sys interface files
are different as shown in block/blk-setting.c:blk_queue_max_sectors().
if (BLK_DEF_MAX_SECTORS > max_sectors)
q->limits.max_hw_sectors = q->limits.max_sectors = max_sectors;
else {
q->limits.max_sectors = BLK_DEF_MAX_SECTORS;
q->limits.max_hw_sectors = max_sectors;
}
I guess, in my case, it enters into the ELSE part. I tried to debug
these sources (block/blk-setting.c), but I am not able to do it.
Please let me know, how can I get the debug statements from this file?
> The value can be changed by writing to
> /sys/block/sdX/device/max_sectors (where X is the drive letter). Note
> that this value is in 512-byte blocks, not in KB. However it is
> limited to SCSI_DEFAULT_MAX_SECTORS, which is 1024, corresponding to
> 512 MB. If larger transfers are needed then
> drivers/usb/storage/scsiglue.c:store_max_sectors() must be changed.
I have chaged the value in /sys/block/sdb/queue/max_sectors_kb through
echo command. Even after this change, I have received only 1024
sectors (512 KB) data transfer buffers in my SCSI command. Even I have
modified the store_max_sectors() function code in the scsiglue.c file.
But, there is no luck and still I received 1024 sectors (512 KB)
transfer buffers in the scsi_command.
Please let me know, if you need any additional information.
Thanks and Regards,
RD.
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