lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <alpine.LFD.0.999.0710260742140.30120@woody.linux-foundation.org> Date: Fri, 26 Oct 2007 07:52:25 -0700 (PDT) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Paul Mackerras <paulus@...ba.org> cc: Rusty Russell <rusty@...tcorp.com.au>, Boaz Harrosh <bharrosh@...asas.com>, Jens Axboe <jens.axboe@...cle.com>, Alan Cox <alan@...rguk.ukuu.org.uk>, Geert Uytterhoeven <geert@...ux-m68k.org>, Linux Kernel Development <linux-kernel@...r.kernel.org>, mingo@...e.hu Subject: Re: [PATCH 09/10] Change table chaining layout On Fri, 26 Oct 2007, Paul Mackerras wrote: > > Linus Torvalds writes: > > > Nobody should *ever* walk the list to find the length. Does anybody really > > do that? Yes, we pass the thing down, but do people *need* it? > > Yes, I need it for devices that use the macintosh DBDMA > (descriptor-based DMA) hardware. The DBDMA hardware reads an array of > descriptors from system RAM, so I need to allocate an array and fill > it in with DBDMA command blocks (and then dma-map it and point the > device at it). Yes, for allocation purposes you'd need the size ahead of time, agreed. Otherwise you have to walk the list twice. > Maybe the drivers for devices that use DBDMA are now buggy. Certainly > filling in the array of DBDMA command blocks involves walking the > list, but it would extremely useful to know how much to allocate > before we start filling them in. So we at least need an upper bound > on the number of "real" entries, even if we don't have the exact > number. Hmm. Depending on where you do this, and if this is some block-layer specific driver/code (rather than necessarily a generic SG thing), you do have the req->nr_phys_segments thing which should be that for you (ie the SG list may have _fewer_ requests in it in case some of those entries got squashed together due to be contiguous). But yeah, I don't think it would be wrong at all to have a struct scatterlist_head { unsigned int entries; unsigned int flags; /* ? */ struct scatterlist *sg; }; which would be passed down at higher levels. Linus - 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/
Powered by blists - more mailing lists