Messages in this thread | | | Date | Sat, 28 Feb 2004 19:58:15 -0500 | From | Jeff Garzik <> | Subject | Re: Worrisome IDE PIO transfers... |
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Bartlomiej Zolnierkiewicz wrote: > [ Geert added to cc: ] > > On Sunday 29 of February 2004 00:24, Jeff Garzik wrote: > >>Looking at the function that is used to transfer data when in PIO mode... >> >>void taskfile_output_data (ide_drive_t *drive, void *buffer, u32 wcount) >>{ >> if (drive->bswap) { >> ata_bswap_data(buffer, wcount); >> HWIF(drive)->ata_output_data(drive, buffer, wcount); >> ata_bswap_data(buffer, wcount); >> } else { >> HWIF(drive)->ata_output_data(drive, buffer, wcount); >> } >>} >> >>Swapping the data in-place is very, very wrong... you don't want to be >>touching the data that userspace might have mmap'd ... Additionally, >>byteswapping back and forth for each PIO sector chews unnecessary CPU. > > > This is used for accessing "normal" disks on beasts with byte-swapped IDE > bus (Atari/Q40/TiVo) and "byteswapped" disks on normal machines. > > [ Hm. actually I don't see how it can be used for accessing "normal" disks, > as data is byteswapped by IDE bus and then swapped back by IDE driver. ]
Yeah, just byteswapped disks are affected.
> Manfred noticed the same issue some time ago: > http://www.ussg.iu.edu/hypermail/linux/kernel/0201.0/0768.html > but discussion ended without final conclusion. > > I like Alan's idea to use loopback instead of "bswap".
Neat but no more zerocopy that way. I much prefer a swap-as-you-go...
>>Seems to me the architecture's OUTS[WL] hook (or a new, similar hook) >>that swaps as it writes would be _much_ preferred, and eliminate this >>possible data corruption issue. > > I think something similar has been already done > (grep for insw_swapw/outsw_swapw in ide-iops.c and asm-m68k/ide.h).
Yeah, but this would need to be per-device... I agree all the other pieces are already present.
Jeff
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