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Date: Sun, 18 Feb 2007 13:37:49 +0100 From: Joerg.Schilling@...us.fraunhofer.de (Joerg Schilling) To: jens.axboe@...cle.com, dougg@...que.net Cc: stern@...land.harvard.edu, linux-kernel@...r.kernel.org, James.Bottomley@...eleye.com Subject: Re: [PATCH] Block layer: separate out queue-oriented ioctls Douglas Gilbert <dougg@...que.net> wrote: > Jens Axboe wrote: > > On Fri, Feb 16 2007, Alan Stern wrote: > >> From: James Bottomley <James.Bottomley@...elEye.com> > >> > >> This patch (as854) separates out the two queue-oriented ioctls from > >> the rest of the block-layer ioctls. The idea is that they should > >> apply to any driver using a request_queue, even if the driver doesn't > >> implement a block-device interface. The prototypical example is the > >> sg driver, to which the patch adds the new interface. > >> > >> This will make it possible for cdrecord and related programs to > >> retrieve reliably the max_sectors value, regardless of whether the > >> user points it to an sr or an sg device. In particular, this will > >> resolve Bugzilla entry #7026. > > > > The block bits are fine with me, the sg calling point is a bit of a sore > > thumb (a char driver calling into block layer ioctls) though. So the > > block layer bits are certainly ok with me, if Doug acks the sg bit I'll > > merge everything up. > > > > (patch left below) > > Does this need to be in the sg driver? > > What is the hardware sector size of a SES or OSD device? > > As for the max_sector variable, wouldn't it be better > to generate a new ioctl that yielded the limit in bytes? > Making a driver variable that implicitly assumes sectors > are 512 bytes in length more visible to the user space > seems like a step in the wrong direction. This is what I did propose. I know of no SCSI device made since 1986 that has a "hardware sector size". This is really a DMA size limit in bytes and if you return the number in an unrelated multiple of a fraction, you will not be able to use the optmium max transfer size. > Alternatively the SG_GET_RESERVED_SIZE ioctl could be > modified to yield no more than max_sectors*512 . This is what I did propose 3 months ago and already 2 years ago. 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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