linux-kernel - Re: [PATCH] Block layer: separate out queue-oriented ioctls Re: [PATCH] Block layer: separate out queue-oriented ioctls

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Date:	Mon, 02 Apr 2007 10:28:18 +0200
From:	Joerg Schilling <schilling@...us.fraunhofer.de>
To:	stern@...land.harvard.edu
Cc:	dougg@...que.net, James.Bottomley@...eleye.com,
	jens.axboe@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Block layer: separate out queue-oriented ioctls Re:
 [PATCH] Block layer: separate out queue-oriented ioctls

Hi,

this is a repost as I like to know the current state of the problem...

The USB DMA size problem is known to exist on Linux since February 2004.
I am still in hope that there will be a fix soon.

/*--------------------------------------------------------------------------*/
Alan Stern <stern@...land.harvard.edu> wrote:

> Well, if Doug wants to reduce the value returned by SG_GET_RESERVED_SIZE, 
> it's okay with me.  An advantage of doing this is that older versions of 
> cdrecord would then work correctly.
>
> However you don't seem to realize that people can use programs like
> cdrecord with devices whose drivers don't support SG_GET_RESERVED_SIZE --
> because that ioctl works only with sg.  Programs would have to try
> SG_GET_RESERVED_SIZE and if it faied, then try BLKSECTGET.

Is there any reason not to have one single ioctl for one basic feature?

> Remember also, the "reserved size" is _not_ the maximum allowed size of a
> DMA transfer.  Rather, it is the size of an internal buffer maintained by
> sg.  It's legal to do an I/O transfer larger than the "reserved size", but 
> it is not legal to do an I/O transfer larger than max_sectors.

At the time the call SG_GET_RESERVED_SIZE has been discussed/defined, we did 
originally agree that the max value should be limited to what the HW allows
as DMA size. This is why I did originally files a bug against 
SG_GET_RESERVED_SIZE.
/*--------------------------------------------------------------------------*/

Jörg

-- 
 EMail:joerg@...ily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
       js@...tu-berlin.de                (uni)  
       schilling@...us.fraunhofer.de     (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.berlios.de/old/private/ ftp://ftp.berlios.de/pub/schily
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