Messages in this thread | | | Date | Fri, 19 May 2006 13:11:30 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] sector_t overflow in block layer |
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"Stephen C. Tweedie" <sct@redhat.com> wrote: > > Hi, > > On Thu, 2006-05-18 at 17:23 -0600, Andreas Dilger wrote: > > > I looked at that also, but it isn't clear from the use of "b_size" here > > that there is any constraint that b_size is a power of two, only that it > > is a multiple of 512. Granted, I don't know whether there are any users > > of such a crazy thing, but the fact that this is in bytes instead of a > > shift made me think twice. > > Yeah. It was very strongly constrained to a power-of-two in the dim and > distant past, when buffer_heads were only ever used for true buffer- > cache data (the entire IO path had to be special-cased for IO that > wasn't from the buffer cache, such as swap IO.) > > But more recently it has been a lot more relaxed, and we've had patches > like Jens' "varyIO" patches on 2.4 which routinely generated odd-sized > b_size buffer_heads when doing raw/direct IO on unaligned disk offsets. > > But in 2.6, I _think_ such paths should be going straight to bio, not > via submit_bh. Direct IO certainly doesn't use bh's any more, and > pretty much any other normal disk IO paths are page-aligned. I might be > missing something, though. >
We use various values of b_size when using a buffer_head for gathering a disk mapping. See, for example, fs/direct-io.c:get_more_blocks().
I don't think we ever play such tricks when a bh is used as an IO container. But we might - I see nothing in submit_bh() which would prevent it.
btw, it seems odd to me that we're trying to handle the device-too-large-for-sector_t problem at the submit_bh() level. What happens if someone uses submit_bio()? Isn't it something we can check at mount time, or partition parsing, or...? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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