[Stgt-devel] [Scst-devel] Integration of SCST in the mainstream Linux kernel

Tue Feb 5 17:21:47 CET 2008

On Tue, 2008-02-05 at 17:07 +0100, Tomasz Chmielewski wrote:
> FUJITA Tomonori schrieb:
> > On Tue, 05 Feb 2008 08:14:01 +0100
> > Tomasz Chmielewski <mangoo at wpkg.org> wrote:
> > 
> >> James Bottomley schrieb:
> >>
> >>> These are both features being independently worked on, are they not?
> >>> Even if they weren't, the combination of the size of SCST in kernel plus
> >>> the problem of having to find a migration path for the current STGT
> >>> users still looks to me to involve the greater amount of work.
> >> I don't want to be mean, but does anyone actually use STGT in
> >> production? Seriously?
> >>
> >> In the latest development version of STGT, it's only possible to stop
> >> the tgtd target daemon using KILL / 9 signal - which also means all
> >> iSCSI initiator connections are corrupted when tgtd target daemon is
> >> started again (kernel upgrade, target daemon upgrade, server reboot etc.).
> > 
> > I don't know what "iSCSI initiator connections are corrupted"
> > mean. But if you reboot a server, how can an iSCSI target
> > implementation keep iSCSI tcp connections?
> 
> The problem with tgtd is that you can't start it (configured) in an
> "atomic" way.
> Usually, one will start tgtd and it's configuration in a script (I 
> replaced some parameters with "..." to make it shorter and more readable):
> 
> 
> tgtd
> tgtadm --op new ...
> tgtadm --lld iscsi --op new ...
> 
> 
> However, this won't work - tgtd goes immediately in the background as it 
> is still starting, and the first tgtadm commands will fail:

this should be a easy fix. start tgtd, get port setup ready in forked
process, then signal its parent that ready to quit. or set port ready in
parent, fork and pass to daemon.

> 
> # bash -x tgtd-start
> + tgtd
> + tgtadm --op new --mode target ...
> tgtadm: can't connect to the tgt daemon, Connection refused
> tgtadm: can't send the request to the tgt daemon, Transport endpoint is 
> not connected
> + tgtadm --lld iscsi --op new --mode account ...
> tgtadm: can't connect to the tgt daemon, Connection refused
> tgtadm: can't send the request to the tgt daemon, Transport endpoint is 
> not connected
> + tgtadm --lld iscsi --op bind --mode account --tid 1 ...
> tgtadm: can't find the target
> + tgtadm --op new --mode logicalunit --tid 1 --lun 1 ...
> tgtadm: can't find the target
> + tgtadm --op bind --mode target --tid 1 -I ALL
> tgtadm: can't find the target
> + tgtadm --op new --mode target --tid 2 ...
> + tgtadm --op new --mode logicalunit --tid 2 --lun 1 ...
> + tgtadm --op bind --mode target --tid 2 -I ALL
> 
> 
> OK, if tgtd takes longer to start, perhaps it's a good idea to sleep a 
> second right after tgtd?
> 
> tgtd
> sleep 1
> tgtadm --op new ...
> tgtadm --lld iscsi --op new ...
> 
> 
> No, it is not a good idea - if tgtd listens on port 3260 *and* is 
> unconfigured yet,  any reconnecting initiator will fail, like below:

this is another easy fix. tgtd started with unconfigured status and then
a tgtadm can configure it and turn it into ready status.

those are really minor usability issue. ( i know it is painful for user,
i agree)

the major problem here is to discuss in architectural wise, which one is
better... linux kernel should have one implementation that is good from
foundation...

> 
> end_request: I/O error, dev sdb, sector 7045192
> Buffer I/O error on device sdb, logical block 880649
> lost page write due to I/O error on sdb
> Aborting journal on device sdb.
> ext3_abort called.
> EXT3-fs error (device sdb): ext3_journal_start_sb: Detected aborted journal
> Remounting filesystem read-only
> end_request: I/O error, dev sdb, sector 7045880
> Buffer I/O error on device sdb, logical block 880735
> lost page write due to I/O error on sdb
> end_request: I/O error, dev sdb, sector 6728
> Buffer I/O error on device sdb, logical block 841
> lost page write due to I/O error on sdb
> end_request: I/O error, dev sdb, sector 7045192
> Buffer I/O error on device sdb, logical block 880649
> lost page write due to I/O error on sdb
> end_request: I/O error, dev sdb, sector 7045880
> Buffer I/O error on device sdb, logical block 880735
> lost page write due to I/O error on sdb
> __journal_remove_journal_head: freeing b_frozen_data
> __journal_remove_journal_head: freeing b_frozen_data
> 
> 
> Ouch.
> 
> So the only way to start/restart tgtd reliably is to do hacks which are 
> needed with yet another iSCSI kernel implementation (IET): use iptables.
> 
> iptables <block iSCSI traffic>
> tgtd
> sleep 1
> tgtadm --op new ...
> tgtadm --lld iscsi --op new ...
> iptables <unblock iSCSI traffic>
> 
> 
> A bit ugly, isn't it?
> Having to tinker with a firewall in order to start a daemon is by no 
> means a sign of a well-tested and mature project.
> 
> That's why I asked how many people use stgt in a production environment 
> - James was worried about a potential migration path for current users.
> 
> 
> 
> -- 
> Tomasz Chmielewski
> http://wpkg.org
> 
> 
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Ming Zhang

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