Perhaps perl is moving your buffer? Does getting a fresh buffer just before the sysread help? (perhaps using tye's suggestion above instead of mmap).

I don't know the pack "p" format very well, but using that to look at the address of $BUFFER appears to show it changing between the first syswrite and the last sysread.

In reply to Re: sysread/syswrite and O_DIRECT alignment problem by jbert
in thread sysread/syswrite and O_DIRECT alignment problem by fishnuts

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