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Re: [Linux-cluster] GFS bug with fcntl/flock ?



Perfect, thank you!!

[root net1 ~]# cd /usr/local/etc/cachesys
[root net1 cachesys]# ll
total 68
-rw-r-Sr--  1 root root  3072 Oct 10 09:22 cache.reg
-r-xr-xr-x  1 root root 35221 Oct 10 09:22 ccontrol
-r-xr-xr-x  1 root root 16609 Oct 10 09:22 csession
[root net1 cachesys]# chmod -s cache.reg
[root net1 cachesys]# ll
total 68
-rw-r--r--  1 root root  3072 Oct 10 09:22 cache.reg
-r-xr-xr-x  1 root root 35221 Oct 10 09:22 ccontrol
-r-xr-xr-x  1 root root 16609 Oct 10 09:22 csession
[root net1 cachesys]# ccontrol all
    Configuration     Version ID        Port   Directory
    ----------------  ----------------  -----  --------------------------------
dn >TOBY              5.0.19.6202.3            /toby/sys


On Fri, 2006-10-13 at 14:15 -0500, Abhijith Das wrote:
Hi Robert,

> I am running InterSystems Caché 5.0.19 for AMD64, and an strace output 
> from their utility reveals a problem with fcntl/flock on the GFS 
> filesystem (mount -t gfs /dev/VGSHARE/lvol0 /usr/local):
>
>     open("/usr/local/etc/cachesys/cache.reg", O_RDONLY|O_NONBLOCK) = 3
>     fcntl(3, F_SETLKW, {type=F_RDLCK, whence=SEEK_SET, start=0,
>     len=0}) = -1 ENOLCK (No locks available)
>
The only place GFS returns ENOLCK is when mandatory locking is turned 
on. It looks like you have the flags for mandatory locking set on this 
particular file. i.e. S_ISGID is set and S_IXGRP is not set. If you do 
an 'ls -al' on this file, you should see something like
    [adas radium locking]$ ls -al templock
    -rwxr-Sr-x  1 adas adas 6 Oct 13 13:50 templock
The 'S' in the permissions for the group indicate mandatory locking. GFS 
does not support mandatory locking and will refuse to
apply fcntl() or flock() on such files.
You can try doing the same fcntl() with start=0 and len=0 on some other 
regular file on gfs and see if that works for you.

> When I put their files on an ordinary ext3 filesystem, all works fine:
>
>     open("/usr/local/etc/cachesys/cache.reg", O_RDONLY|O_NONBLOCK) = 3
>     fcntl(3, F_SETLKW, {type=F_RDLCK, whence=SEEK_SET, start=0,
>     len=0}) = 0
>
When you copied the files over, they might have lost these flags, or 
your ext3 fs supports mandatory locking ('-o mand' mount option)

> The man page on fcntl states that when flock is setup with 
> whence=SEEK_SET, start=0, and len=0, the lock will occur on the entire 
> file... so locking zero bytes in this manner is acceptable.  Help?

This works correctly in my test environment.

Hope this helps.

Regards,
--Abhi

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Robert Hurst, Sr. Caché Administrator
Beth Israel Deaconess Medical Center
1135 Tremont Street, REN-7
Boston, Massachusetts   02120-2140
617-754-8754 ∙ Fax: 617-754-8730 ∙ Cell: 401-787-3154
Any technology distinguishable from magic is insufficiently advanced.

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