Re: [9fans] 9p questions

Re: [9fans] 9p questions

[steve.simon]

Hi,

Thanks rog for your comments.

I forgot to say the app that caused problems with renaming open files was
CVS, which doesn't bother closing temporary files before moving
them into place.

Just closing the file worked fine here (fd leak in CVS?) and got me using
ncpfs in anger (read thorough testing :-), but a better solution is really
required.

-Steve

[9fans] 9p questions

[steve.simon]

Hi,

two questions about 9p semantics:

1/
Netware will not let me rename a file which is open.

So, when wstat updates a file's name does 9p place a
restriction on wether the file is open or not?

Do I have to do a close, rename and reopen on rename
or is just close safe? I guess the answer is reopen
the file - more races :-(

Netware has similar restrictions on deleteing files/dirs so
I am closing then also,  but I cannot imagine any side
effects from this.

2/
Netware changes its file ID (which I map to Qid) when
a file is renamed.

Using lib9p is it OK to change fid->qid in wstat, under the
libraries feet so to speak?

Also, will it mess up plan9 clients?

-Steve

Re: [9fans] 9p questions

[rog]

> So, when wstat updates a file's name does 9p place a
> restriction on wether the file is open or not?

no - you can wstat whether the file is open or not (fwstat, wstat).

you could always return an error if a rename was attempted when the
file was open.  presumably the file can be currently open by another
user, so i'd assume doing a close/rename/reopen is unlikely to be
sufficient in general.

i don't know if much plan 9 infrastructure relies on being able to use
fwstat to rename a file (the most likely candidate, upas, doesn't use
fwstat to rename the mbox, but then again it might easily be holding
another fd open on it).

> Netware has similar restrictions on deleteing files/dirs so
> I am closing then also,  but I cannot imagine any side
> effects from this.

remove is a clunk anyway, so no problems there (apart from
if another process has it open, as above, but nothing you can
do there).

> Using lib9p is it OK to change fid->qid in wstat, under the
> libraries feet so to speak?

this is fairly dodgy; the only times AFAIK that a qid corresponding
to a fid can be changed are attach, create, open and walk,
and all these return the new qid in the rmsg.

> Also, will it mess up plan9 clients?

good question...
'cos i know it's difficult verging on impossible to manufacture a
proper qid space for some imported filesystems.

i know that inferno used a hash of the filename for its ntfs
filesystem under windows for quite a while, and most things worked ok.
i think it still does the same thing, with the exception that a file
which has been walked to keeps the same qid for as long as there's a
reference to it.

this ensures that a bind onto a directory stays put even though the
directory has been renamed, but it's not perfect.  i may be wrong
about this too, as i didn't have anything to do with the changes.

  cheers,
    rog.