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

[Mike Anderson]

Chandra Seetharaman <sekharan at us.ibm.com> wrote:
> 
> On Wed, 2010-04-21 at 19:51 +1000, ronnie sahlberg wrote:
> > 
> > 
> > Tomo, would a patch that allows setting the O_DIRECT/O_SYNC flags on
> > the command line when invoking tgtd be acceptable?
> > 
> > 
> > 
> > 
> > tgtd -o O_SYNC     tgtd -o O_DIRECT      tgtd -o O_SYNC|O_DIRECT
> > 
> > 
> > 
> > The appropriate flags in the caching mode page could be intercepted
> > and use to toggle these fd settings.
> > 
> > My filesystem of choice would likely benefit greatly from O_DIRECT.
> 
> I see the feature being useful.
> 
> But, I would associate this to be a characteristic of the backing store
> than set it globally at tgtd (or we can have a it at global(read tgtd
> level) and ability to revert it at the backing store).
> > 

If we associate the open flags to the backing store would we want to allow
full control of the open flags or just setting a subset of flags.

I hacked up tgtadm and a few of the target.c functions for the examples below.

./tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1 -b /disk1
--bsoflags "O_RDWR| O_LARGEFILE | O_DIRECT" --device-type disk

or

tgtadm --op update --mode logicalunit --tid 1 --lun 1 --params bsoflags="O_RDWR| O_LARGEFILE | O_DIRECT"

./tgtadm --op show --mode target
...
      LUN: 1
            Type: disk
            SCSI ID: IET     00010001
            SCSI SN: beaf11
            Size: 105 MB
            Online: Yes
            Removable media: No
            Backing store type: rdwr
            Backing store flags: O_RDWR | O_LARGEFILE | O_DIRECT
            Backing store path: /disk1
...

-andmike
--
Michael Anderson
andmike at linux.vnet.ibm.com
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