Re: Linux scsi / usb-mass-storage and HP printer cardreader bug + fix

----- Original Message -----
*From:* Hans de Goede <[email protected]>
*To:* USB Storage list <[email protected]>
*CC:* [email protected], USB development list
<[email protected]>, David Brown
<[email protected]>, Guillaume Bedot <[email protected]>,
[email protected], [email protected]
*Sent:* Wed, Jan 09 2008 at 23:44 +0200
*Subject:* Linux scsi / usb-mass-storage and HP printer cardreader bug + fix


> Hi All,
>
> First of all sorry for the somewhat massive cross-posting, I've spend a 
> significant amount of time hunting down this bug, and so far the response has 
> been less the overwhelming.
>
> The problem is with the HP PSC 1350 (my printer and confirmed by 2 others) and 
> atleast also the HP PSC 1610 (confirmed by Guillaume Bedot, in the CC).
>
> The cardreader of the multi function printers will "crash" and from that moment 
> on no longer communicate in any sane way, if you try to read the last sector of 
> an sdcard* in a read that is more then 1 sector, so trying to read 8 sectors 
> starting at sector capicity-8 will crash it, as will reading 2 sectors starting 
> at sector capicity-2, however reading the last sector in a one 1 sector read 
> will succeed! (* xdcards seem to be fine).
>
> I haven't tried if it will crash on larger then 1 sector writes which include 
> the last sector too, I immediately added code to not do that in both the read 
> and write paths. I have tested reading and writing the end of the disk with 
> this kludge in and it works.
>
> I currently have a somewhat ugly proof of concept patch for this, which adds 
> another type of usb-massstorage quirk. When this quirk flag is set, the 
> usb-massstorage driver modifies READ_10 and WRITE_10 commands of more then 1 
> sector which includes the last sector to become one sector less. I've been told 
> by scsi subsystem developers that doing a shorter read / write then requested 
> is not a problem, the scsi subsystem is designed to handle getting less then it 
> asked for and will send a seperate request for the last sector.
>
> I and 3 others (2 on a PSC 1350 too, one on a PSC1610) have tested this patch 
> with success. I'm not asking for this patch to be included to the kernel as is, 
> I'm asking for the now known workaround for this to be added to the kernel in 
> someway!
>
> Perhaps its an idea to add the posibility to have a scsi command filter 
> function / callback to the scsi or usb-massstorage subsystem, and then add a 
> mechanism to set this filter depending on usb id's and if added to the scsi 
> layer, a mechanism to set it based on scsi device and manufacturer 
> identification strings. Such a mechanism might be usefull in the future to work 
> around other broken hardware too, and has the added advantage of not having 
> todo much changes to the normal code path, keep that readable.
>
> I'm willing to come up with a patch for such a filter mechanism, provided I get 
> some pointers where this is best added.
>
> Thanks & Regards,
>
> Hans
>
>
> p.s.
>
> I've also included the fedora-kernel list in the addressee's because I was 
> hoping that maybe someone can take one of these printers to the kernel hackfest 
>    in the weekend's fudcon and take a look at this.
>   
> +		if ((offset + num) == sdkp->capacity && num > 1) {
> +			if (srb->cmnd[8] == 0)
> +				srb->cmnd[7]--;
> +			srb->cmnd[8]--;
> +			srb->request_bufflen -= 512;
> +			srb->underflow -= 512;
> +		}
>   
This will no longer compile on top of latest scsi-misc, and
LLDs are not suppose to modify request_bufflen anymore.

I'm not sure what the proper solution should be?

Boaz


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