Nicholas A. Bellinger wrote:
On Thu, 2008-08-21 at 18:31 -0500, Mike Christie wrote:
snip
Ok, I took in the weekend to let things settle for a few moments..
If all necessary pieces of STGT moved in the kernel, it would become
pretty much the same as SCST at the moment.
In the top paragraph James is saying to move scst into stgt, so it seems
like we can do the following:
1. You and with Nick battle each other about what are the best pieces of
scst and his target and what should go upstream.
Ok, Vlad and I have discussed and determined that the process will be
something roughly along the lines of
*) Vlad releases upstream patches for SCST Core in the late v2.6.27 time
frame.
*) /me will cherry picks from lio-core-2.6.git specific code (namely the
memory allocation and mapping algorithms) and begin to integrate these
into SCST-Core upstream and get bulk I/O moving between SCST Core
kernel/user CDB generation API.
*) Around the same time, I will begin the porting process of moving
LIO-Target to use the new upstream target infrastructure, whatever it
shall be called.. :-)
I agree
Our userspace tools will also be able to support both kernel space and
userspace targets with little trouble so distros that have stgt will not
notice any differences.
So this is one of the items that I mentioned to Vlad as being a
potential stumbling block.. I stated that I have no problem dumping the
LIO IOCTL in favor of something better, and having to break backwards
compat with LIO userspace tools (well, until I have to emulate the
backwards compat wrt target-ctl ;-)) is something I am ready to deal
with.
So I definately see your point here, having the exist CLI logic in place
into distros is something that we are going to have to deal with (even
if the core behind them is completely different).
I should also mention that virtually all of the configuration logic done
from the LIO-Core and LIO-Target IOCTLs today is intended (minus a bug
or two :-) to be done without having to shutdown/stop anything other
than the referenced object for the target-ctl operation. Obviously, I
really want to keep the same functionality with the CLI interface the
LIO pieces are ported to.
I will be sure to take a look at the STGT control interface and see how
I can fit the current functionality in. I believe SCST uses an IOCTL
today as well, which would put them in a similar situation.
I, personally, don't like an interface, like tgtadm, which tries to do
all non-trivial configuration work from a single command line tool,
because of the following 3 reasons:
1. It's a lot of effort to write and maintain such a tool, because it
needs to be extensible to work with new modules and modes. For instance,
iptables tool is 86K lines long. The whole netfilter code for all
network protocols in the kernel is less that 50K lines long. Do we want
such a code bloat (170% of code to configure) and dedicated team of
maintainers to solve a fundamentally simple configuration task?
2. It assumes the stateless type of configuration, when each call
configures exactly one thing without any side effects on already
configured or future entries. This approach is good for cases like
iptables, but for SCSI targets it's possible that several configuration
steps require to be done in an atomic manner, like adding an iSCSI
target and configuring its parameters.
3. It's hard to read 5+ parameters in one command line, so it's a lot
easier to make a mistake there.
So, I believe, a configuration interface should be rather /proc or /sys
interface based. I don't think we should care much about backward
compatibility with tgtadm, because the existing interface doesn't reach
the state of being widely used. As I already mentioned, only ibmvscsi at
the moment uses it, hardware for which is pretty rare.
Thus, I would suggest that before making the further move we should also
consider configuration interfaces of SCST and LIO and choose the best
things from all 3.
Vlad
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