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

From: Joerg Schilling
Date: Mon Feb 19 2007 - 11:11:32 EST

Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> 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


EMail:joerg@xxxxxxxxxxxxxxxxxxxxxxxxxxx (home) Jörg Schilling D-13353 Berlin
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