samba - Apr 2009 - blocking file locks

Hello all,

As a Samba programming newbie, I've run onto a question that doesn't
have an
obvious answer in FAQ or googled literature. I need to lock large numbers of
files on the server, and have Samba open requests block until they are
released. I found references to "blocking locks" in references such as
"Using Samba" (O'Reilly, 1999, 2003)

http://oreilly.com/catalog/samba/chapter/book/ch05_05.html

but these refer to range locks, which are overkill for my application (I
only need to check on open, not on every IO).

Deny modes would seem to fill the bill, but I can't find whether blocking
locks would work for them, and also they do not seem to be Linux-compatible
on the server, and I suspect I may need that for efficiency's sake (a lot of
files are being locked/unlocked). I downloaded samba-latest.tar.gz and
noticed that source/smbd/blocking.c seems to respond to these by setting
LOCK_MAND versions of flock states, which are available only for
"sys_flock"
and rumored not to affect normal Linux programming.

Can file locks block a Samba open request? Can they be set by, or made to
affect, Linux programming on the server (I don't care about NFS file opens,
only local opens on the server)? Does this drive special Samba kernel code,
or does smbd just operate in user space?

TIA,

Larry Dickson
Cutting Edge Networked Storage

On Tue, Apr 21, 2009 at 09:53:37AM -0800, Larry Dickson
wrote:
> Hello all,
> 
> As a Samba programming newbie, I've run onto a question that
doesn't have an
> obvious answer in FAQ or googled literature. I need to lock large numbers
of
> files on the server, and have Samba open requests block until they are
> released. I found references to "blocking locks" in references
such as
> "Using Samba" (O'Reilly, 1999, 2003)
> 
> http://oreilly.com/catalog/samba/chapter/book/ch05_05.html
> 
> but these refer to range locks, which are overkill for my application (I
> only need to check on open, not on every IO).
> 
> Deny modes would seem to fill the bill, but I can't find whether
blocking
> locks would work for them, and also they do not seem to be Linux-compatible
> on the server, and I suspect I may need that for efficiency's sake (a
lot of
> files are being locked/unlocked). I downloaded samba-latest.tar.gz and
> noticed that source/smbd/blocking.c seems to respond to these by setting
> LOCK_MAND versions of flock states, which are available only for
"sys_flock"
> and rumored not to affect normal Linux programming.
> 
> Can file locks block a Samba open request? Can they be set by, or made to
> affect, Linux programming on the server (I don't care about NFS file
opens,
> only local opens on the server)? Does this drive special Samba kernel code,
> or does smbd just operate in user space?
File locks can't block an open request. On a Linux kernel
you can use file leases to prevent other local opens.

Jeremy.