On 5/30/13 7:17 AM, Andres Freund wrote:
That argument in contrast I find not very convincing though. What was the last incidence of such a system call that did not just error out with ENOTSUPP or such?
http://linux.die.net/man/2/posix_fadvise talks about POSIX_FADV_NOREUSE and POSIX_FADV_WILLNEED being both buggy and quietly mapped to a no-op, depending on your version. I know there were more examples than just that one that popped up during the testing of effective_io_concurrency. My starting position has to assume that posix_fallocate can have the same sort of surprising behavior that showed up repeatedly when we were trying to use posix_fadvise more aggressively.
The way O_SYNC was quietly mapped to O_DSYNC (which isn't the same thing) was a similar issue, and that's the first one that left me forever skeptical of Linux kernel claims in this area until they are explicitly validated: http://lwn.net/Articles/350225/
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