Re: [RFC][PATCH] nbd driver for 2.5+: fix locking issues with ioctl

Lou Langholtz (ldl@aros.net)
Wed, 25 Jun 2003 08:24:18 -0600


Andrew Morton wrote:

>Lou Langholtz <ldl@aros.net> wrote:
>
>
>>That said, this seems like an opportunistic time to further break
>> compatibility with the existing nbd-client user tool and do away with
>> the problematic components of the ioctl user interface.
>>
>>
>
>Is a suitably modified userspace tool available?
>
>
Seems like a pandora's box (and/or catch-22)... A modified userspace
tool is not yet available that I know of. I have a hacked version that
I've been using to test things with of course. But it's not in a very
nice state to release. And then Pavel's distro of the tool is probably
what most people use anyway. I have a seperate distro in part because I
wanted to just play with things at first and thought sharing the sources
might be useful to someone. Etc. Anyways, I wanted to get a feeling
first from the kernel hacking community how important back compatibility
was to them w.r.t. this driver. Since the original jumbo patch also got
criticized against for supporting multiple linux version in the driver
sources (via the LINUX_VERSION macros), seems like there's some split in
what people may prefer. I wanted to generate comments on these specific
changes to solidify what changes would really be needed in the user
space tool before also distributing a changed nbd-client. It would also
help to have something like a version ioctl or something that could be
keyed on to provide the correct support. On the other hand, I'm not sure
that Pavel even realized that the block layer changes impacted the
semantics of the sizing ioctl (such that the user-space tool needs to
re-open the file descriptor to get the proper size in). I didn't realize
this myself even till only a few days ago but I had been wondering all
along why sizing hadn't been working right. Sigh. Just to many other
things to also do. The driver could also fix this sizing issue but
coding the change their feels more like a hack than in the client tool.
On the bright side, Pavel's nbd-client could probably be ifdef'd quite
easily to work-around/fix the sizing issue and also this new proposed
ioctl interface. Let me catch up w/ LKML mail and see what others have
to say so far. I can probably produce a diff for Pavel easily enough
(more easily than for my distro of the same) so that we won't have these
issues anymore. But then full circle, it all depends on how the
community would like to see these issues resolved (ie. maybe they want
the sizing fixed in the driver instead and personally it's a close balance).

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