[stgt] Write-cache in tgtd during a target-host crash

[FUJITA Tomonori]

On Wed, 21 Apr 2010 19:51:49 +1000
ronnie sahlberg <ronniesahlberg at gmail.com> wrote:

> It would also be very useful to tell tgtd to use either or both of
> O_SYNC/O_DIRECT for all i/o depending on the semantics of the
> filesystem used to hos the lun files.

tgt opens a file with just O_LARGEFILE. If you enable the writeback
cache (on the target or initiator), tgt issues write and
sync_file_range system calls.

WCE bit can be changed at runtime, so I'm not sure using O_SYNC for
the writeback cache.

About O_DIRECT, what's the advantage of using O_DIRECT?

Note that you configure tgt to use AIO, tgts uses
O_LARGEFILE|O_DIRECT.
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