[stgt] Write-cache in tgtd during a target-host crash
ronniesahlberg at gmail.com
Thu Apr 22 00:04:20 CEST 2010
I think one should only be able to set a subset of the flags and have
other flags such as O_RDWR and O_LARGEFILE
always be set.
Otherwise someone might try to create a readonly lun by setting
O_RDONLY instead of O_RDWR and while it will not be possible to write
to the LUN, this would break on the initiator side since true readonly
would require a bit more than failing to write. (such as different
data in mode sense as well as specific sense codes when refusing a
On Thu, Apr 22, 2010 at 7:44 AM, Mike Anderson
<andmike at linux.vnet.ibm.com> wrote:
> 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
> 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
> Michael Anderson
> andmike at linux.vnet.ibm.com
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