On Fri, 2005-09-30 at 16:32 -0400, Luben Tuikov wrote:
> On 09/30/05 16:14, Andrew Patterson wrote:
> >
> > Yes you can, which is what I am trying to do. However, is that library
> > also available on Solaris and Windows? Is it up to date? These are the
>
> Is the kernel the latest one? Is it up to date?
>
> See? Same argument.
>
> >>>Note that a sysfs implementation has problems. Binary attributes are
> >>>discouraged/not-allowed.
> >>
> >>I've never heard that. Is this similar to the argument
> >>"The sysfs tree would be too deep?"
> >
> >
> >>From Documentation/filesystes/sysfs.txt
> >
> > "Attributes should be ASCII text files, preferably with only one value
> > per file. It is noted that it may not be efficient to contain only
> > value per file, so it is socially acceptable to express an array of
> > values of the same type.
> >
> > Mixing types, expressing multiple lines of data, and doing fancy
> > formatting of data is heavily frowned upon. Doing these things may get
> > you publically humiliated and your code rewritten without notice."
>
> I see this talk _only_ about non-binary attributes.
I think that "ASCII text files" implies non-binary. As Willy has pointed
out, this has already been violated.
>
> Plus you have to admit: the SAS sysfs "smp_portal" binary
> attribute is very versatile: you completely control the
> expander from user space _if_ you can see it: It is
> almost like "point and click".
No problem with this.
>
> I imagine there would be GUIs built on top of it, which would
> actually implement that "point, click, control".
>
> > My understanding is that sysfs is meant to be human-readable. I do not
>
> But `cat /sysfs/.../smp_portal` _is_ human readable. See? Its size is
> 0 bytes and when you read it you get 0 data read.
I don't quite think your definition of human readable is the same as
mine. I think the intention is to do something like:
$ cat attribute
3 Gb/s
or
$ echo "3 Gb/s" >attribute
Rather than
$ cat attribute
gibberish.
or
$ echo "gibberish" >attribute
But again, this may be just a goal and not a hard and fast rule. I can
definitely see a use for binary attributes in sysfs. Configfs seems to
be designed for this sort of thing.
>
> > User space locking can only guarantee atomic operations in user space.
>
> And user space is the whole audience of this interface.
>
> > Not sure at the moment, can I guarantee this for the future?
>
> How far in the future? 1, 3, 6 months? 1, 3, 6 years?
> Plus if you need an attribute larger than 4K, you've got
> other problems to worry about.
>
> > There are as many as one would want. We now have 32 bit device numbers.
> > Old technology is fine as long as it works, especially if their is no
> > new technology to replace it. Note that I don't like the character
> > device solution either. What would really be nice is something that will
> > allow us to pass an arbitrary request buffer, and get an arbitrary
> > response buffer back in a single transaction,
> , locks it, then hangs.
> Here:
>
> /* User space lock */
>
> fd = open(smp_portal, ...);
> write(fd, smp_req, smp_req_size);
> read(fd, smp_resp, smp_resp_size);
> close(fd);
>
> /* User space unlock */
>
> > See above. This stuff works for trivial user-space apps. It will not
> > suffice for most storage management apps.
>
> Sorry but I completely fail to see this argument., locks it, then hangs.
>
> How will it "fail for most storage managament apps"?
Let's see, one example:
Process A opens an attribute and writes to it. Process B opens another
attribute and writes to it, affecting the result that process A will see
from its subsequent read. I suppose you could lock every attribute, but
that would be very error-prone, and not allow much concurrency.
Andrew
>
> Luben
>
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