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

[Lars Melin <larsm17-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 2014-07-07 22:39, loody wrote:
> hi David:
>
> 2014-07-07 23:06 GMT+08:00 David Laight <David.Laight-JxhZ9S5GRejQT0dZR+AlfA@public.gmane.org>:
>> 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,
dd if=/dev/sda of=/dev/null count=1
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