[linux-cifs-client] tail -f /mounted/share/filename is not working

[Günter Kukkukk]

Am Freitag, 20. März 2009 schrieb Suresh Jayaraman:
> � wrote:
> > Hi Steve, Jeff,
> > 
> > this one is on my todo list for more than a year now.
> 
> May be this behavior has changed now?  I tried to reproduce this on
> 2.6.27.19 with directio option against a Samba-3.0.26 server. I could
> not reproduce this at all (I used tail instead of statgk). I'm
> seeing the stuff written with negligible delay on the client.
> 
> Are you able to reproduce this with the recent kernels? If yes, are you
> getting more clues as to what is happening with a tcpdump/cifsFYI ?

About a year ago i had some short irc talk with Jeff about this tail -f ..
problem, but we dropped it, cause other stuff had higher priority.

I actually do my tests on Steve's recent git kernel tree - so 2.6.29-rc7 -
against recent samba_v-3-3-test.
As i already mentioned
    "Btw - when using the mount option "directio", all _seems_ to be fine."
the tail -f ... problem is only seen here when "directio" is _not_ used.

The wire traffic to the server is only a repeated 
   QUERY_PATH_INFO (Query File Unix Basic)
as requested periodically from the clients program fstat()

Btw - my statgk applet has some advantages over 'tail' when debugging this, by also
listing the size (..) change - and showing the ability to really read the appended
line(s) - and list it as ASCII and also as some first hex bytes (which are often nil here).
 
In inode.c --> cifs_revalidate() the var "invalidate_inode" is correctly set true.

To me, the problematic part is inside this code fragment:

-----------------------
	if (invalidate_inode) {
	/* shrink_dcache not necessary now that cifs dentry ops
	are exported for negative dentries */
/*		if (S_ISDIR(direntry->d_inode->i_mode))
			shrink_dcache_parent(direntry); */
		if (S_ISREG(direntry->d_inode->i_mode)) {
			if (direntry->d_inode->i_mapping) {
				wbrc = filemap_fdatawait(direntry->d_inode->i_mapping);
				if (wbrc)
					CIFS_I(direntry->d_inode)->write_behind_rc = wbrc;
			}
			/* may eventually have to do this for open files too */
			if (list_empty(&(cifsInode->openFileList))) {
				/* changed on server - flush read ahead pages */
				cFYI(1, ("Invalidating read ahead data on "
					 "closed file"));
				invalidate_remote_inode(direntry->d_inode);
			}
		}
	}

-------------------------------

The code path to use 
     invalidate_remote_inode(direntry->d_inode);
is not hit.
(when i force "invalidate_remote_inode(direntry->d_inode);" here, all
looks much better)

Sorry, when i'm wrong here. :-)

Cheers, Günter
 
> 
> > 
> > How to test:
> >   server side: use "./wrt filename" or "./wrt -s 100 filename"
> >                to start writing/appending to a file on a (samba) exported share
> >                (regarding the '-s' option, I though writing large data would/could
> >                 trigger some cifs "re-read server" internals (page dirty...))
> >   cifs client side: (one might use 'tail -f /mnt/xyz/filename' as well)
> >                     use ./statgk /mnt/xyz/filename
> > 
> > On the cifs client side "statgk" uses fstat() to get possible _updated_
> > file info from the server (filesize, times, ...) - cifs *realizes* (!) the size (times) change,
> > but no "read additional data" from the server is done.
> > 
> 
> Thanks,
>