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

[Joerg.Schilling@fokus.fraunhofer.de (Joerg Schilling)]

Alan Stern <stern@rowland.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

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