On Thu, Mar 26, 2009 at 2:24 AM, Jeff Garzik <jeff@garzik.org> wrote:
quoted text
> Kyle Moffett wrote:
>> Really, I think virtually all of the database programs would be
>> perfectly happy with an "fsbarrier(fd, flags)" syscall, where if "fd"
>> points to a regular file or directory then it instructs the underlying
>> filesystem to do whatever internal barrier it supports, and if not
>> just fail with -ENOTSUPP (so you can fall back to fdatasync(), etc).
>> Perhaps "flags" would allow a "data" or "metadata" barrier, but if not
>> it's not a big issue.
>
> If you want a per-fd barrier call, there is always sync_file_range(2)

The issue is that sync_file_range doesn't seem to be documented to
have any inter-file barrier semantics.  Even then, from the manpage it
doesn't look like
write(fd)+sync_file_range(fd,SYNC_FILE_RANGE_WRITE)+write(fd) would
actually prevent the second write from occurring before the first has
actually hit disk (assuming both are within the specified range).

Cheers,
Kyle Moffett
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