On Thu, Jul 11, 2024 at 10:16 PM, 龙重余 wrote: > Hello! > > > I'm sorry to bother you. Here is the problem: My usb storage device > has a 64kB (limited by hardware) buffer used to cache reads/writes > which means it can only cache up to 128 blocks(512B) of memory. The > SCSI Write-10 and Read-10 command has a total-blocks field that can be > up to 240 blocks (120kB) for USB2.0. When originally testing the > product on Windows 11 it never writes more than 128 blocks at a time > but when tested on Linux it sometimes writes more than 128 blocks, > which causes the usb storage device to crash. > > > Is there a way to tell the host OS not to request more than 128 blocks? > I have implemented block limit VPD page, and it works well on Windows > 10/11. I even set the block limit to be 64 blocks, it's OK too. > Because before the data transfer, the windows host issue an SCSI > inquiry order with the VPD PAGE CODE is 0xB0, so the device could > transmit the block limits information to the host. And then the > windows host could adjust the amount of data transferred. > > However, on Linux or MacOS, the host does not appear to be running the > block limits command. So the host don't know what is the block > limits. So the write/read blocks number beyond the buffer size. > > > Could you please tell me what can I do to dissolve the problem? (Note that this is really a SCSI question, not a USB question.) You tell the Linux host the maximum number of sectors the device's hardware can transfer in a single command by writing to the max_hw_sectors_kb file in sysfs. For example, if your device shows up as /dev/sdc then you could do: echo 64 >/sys/block/sdc/queue/max_hw_sectors_kb You can even write a udev script to do this for you automatically whenever the storage device is detected. I don't know why this doesn't happen automatically. Maybe the SCSI layer doesn't try to read VPD page 0xb0 on USB mass-storage devices. You should be able to find out by asking on the linux-scsi@xxxxxxxxxxxxxxx mailing list. Alan Stern
