Re: dummy scsi read or scsi command periodically for external USB Hard Disk

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hi David:

2014-07-07 23:06 GMT+08:00 David Laight <David.Laight@xxxxxxxxxx>:
> From: Lars Melin
> ...
>> sgread is not included in BusyBox but you should have "touch".
>> Create a dummy file on the disk and let cron touch it every 4 minutes.
>
> You don't need 'touch' a shell redirect eg ": >file" will do open(..., O_CREAT|O_TRUNC).
> However that still might not force an actual disc access.
>
> In any case you really only want to do a read, doing a write will kill the NAND memory.

actually I have searched the scsi/usb layer for possible dummy read,
even read sector 0 is fine, but in vain.

I found the read
a. determined by VFS -> block layer,
b. Block layer put it in queue
c. call scsi pre-queue function to usb layer.

That mean if I try to read sector from usb devices, I have to create a
queue and follow above b) and c) rule.
is there any already kernel API I can use?

sincerely appreciate all yours help,
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