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From: (Joerg Schilling)
Subject: Re: [PATCH] Block layer: separate out queue-oriented ioctls
Date: Mon, 19 Feb 2007 17:08:18 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Alan Stern <> 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 


-- (home) Jörg Schilling D-13353 Berlin                (uni)     (work) Blog:

  reply	other threads:[~2007-02-19 16:11 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-16 19:37 Alan Stern
2007-02-17  6:28 ` Jens Axboe
2007-02-17 21:18   ` Joerg Schilling
2007-02-18  3:43   ` Douglas Gilbert
2007-02-18 12:37     ` Joerg Schilling
2007-02-18 16:44     ` Alan Stern
2007-02-18 18:27       ` Joerg Schilling
2007-02-19 16:06         ` Alan Stern
2007-02-19 16:08           ` Joerg Schilling [this message]
2007-02-19 17:06             ` Alan Stern
2007-02-19 22:25               ` Douglas Gilbert
2007-02-20  3:48                 ` Alan Stern
2007-02-20  4:47                   ` Douglas Gilbert
2007-02-20 15:55                     ` Alan Stern
2007-04-26  9:19                 ` Joerg Schilling
2007-04-26 15:04                   ` Alan Stern
2007-04-26 15:08                     ` James Bottomley

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