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    SubjectRe: A new ide warning message
    On Fri, Aug 02 2002, Bartlomiej Zolnierkiewicz wrote:
    >
    > On Fri, 2 Aug 2002, Jens Axboe wrote:
    >
    > > On Fri, Aug 02 2002, Jens Axboe wrote:
    > > > On Fri, Aug 02 2002, Marcin Dalecki wrote:
    > > > > U?ytkownik Stephen Lord napisa?:
    > > > > >In 2.5.30 I started getting these warning messages out ide during
    > > > > >the mount of an XFS filesystem:
    > > > > >
    > > > > >ide-dma: received 1 phys segments, build 2
    > > > > >
    > > > > >Can anyone translate that into English please.
    > > > >
    > > > > It can be found in pcidma.c.
    > > > > It is repoting that we have one physical segment needed by
    > > > > the request in question but the sctter gather list allocation
    > > > > needed to break it up for mapping in two.
    > > >
    > > > You don't seem to realise that this is a BUG (somewhere, could even be
    > > > in the generic mapping functions)! blk_rq_map_sg() must never map a
    > > > request to more entries that rq->nr_segments, that's just very wrong.
    > > >
    > > > That's why I'm suspecting the recent pcidma changes. Just a feeling, I
    > > > have not looked at them.
    > >
    > > I'll take that back. Having looked at Adam's changes there are perfectly
    > > fine. I'm now putting my money on IDE breakage somewhere instead. It
    >
    > Look again Jens. Adam's changes made IDE queue handling inconsistent.
    > hint: 2 * 127 != 255
    >
    > But noticed warning deals with design of ll_rw_blk.c. ;-)
    > (right now max_segment_size have to be max bv->bv_len aligned)

    Yeah that's true, actually was just saying that on linux-scsi
    yesterday/today.

    > Jens, please look at segment checking/counting code, it does it on
    > bv->bv_len (4kb most likely) not sector granuality...
    >
    > So for not 4kb aligned max_segment_size we will get new segment...
    >
    > Best fix will be to make block layer count sectors not bv->bv_len...

    Well I'm inclined to just make that page size granularity. It's like
    that in 2.4 as well (no guarentees that we will honor anything less than
    that granularity).

    > btw. I like Adam's patch but it was draft not to include in mainline (?).

    The concept is sound, so it has a bug... I can say the same for other
    stuff in the kernel as well :-)

    I probably just wanted more review (my 1 minute review surely wasn't
    enough).

    --
    Jens Axboe

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