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    SubjectRe: A problem about DIRECT IO on ext3
    On Mon, 17 Oct 2005, Jens Axboe wrote:
    >> how to correct this problem ?
    >
    > See your buffer address, it's not aligned. You need to align that as
    > well. This is needed because the hardware will dma directly to the user
    > buffer, and to be on the safe side we require the same alignment as the
    > block layer will normally generate for file system io.
    >
    > So in short, just align your read buffer to the same as your block size
    > and you will be fine. Example:
    >
    > #define BS (4096)
    > #define MASK (BS - 1)
    > #define ALIGN(buf) (((unsigned long) (buf) + MASK) & ~(MASK))
    >
    > char *ptr = malloc(BS + MASK);
    > char *buf = (char *) ALIGN(ptr);
    >
    > read(fd, buf, BS);

    Shouldn't one use posix_memalign(3) for that?


    Grzegorz Kulewski
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