Ext3 users - Apr 2002 - Help with file locking

Hello;

We are working on an application that needs to grab files put onto an ext3
filesystem as soon as they are written.  We've looked at lsof, and other
tools, and are having troubles finding just the right mechanism to tell when
a file has been completely written and the other process has closed the
file.

In most cases it will be Samba users putting the files onto the ext3
filesystem that we need to process immediatitely, and we will also need to
allow NFS users to put files onto the ext3 filesystem.  In both cases, we
need low-level knowledge of when the file is written completely so we can
grab the sucker right away.

Any help would be appreciated!

John Fraser
VisionShare Inc.

Hi,

On Sun, Apr 14, 2002 at 08:07:19AM -0500, John Fraser
wrote:
> 
> We are working on an application that needs to grab files put onto an ext3
> filesystem as soon as they are written.  We've looked at lsof, and
other
> tools, and are having troubles finding just the right mechanism to tell
when
> a file has been completely written and the other process has closed the
> file.
There isn't one, basically.
> allow NFS users to put files onto the ext3 filesystem.  In both cases, we
> need low-level knowledge of when the file is written completely so we can
> grab the sucker right away.
No such interface exists, but you have the source, you could write
one!

--Stephen

John Fraser wrote:
> 
> Hello;
> 
> We are working on an application that needs to grab files put onto an ext3
> filesystem as soon as they are written.  We've looked at lsof, and
other
> tools, and are having troubles finding just the right mechanism to tell
when
> a file has been completely written and the other process has closed the
> file.
> 
> In most cases it will be Samba users putting the files onto the ext3
> filesystem that we need to process immediatitely, and we will also need to
> allow NFS users to put files onto the ext3 filesystem.  In both cases, we
> need low-level knowledge of when the file is written completely so we can
> grab the sucker right away.
> 
That actually sounds like a fairly useful feature addition
for the directory notification code.

include/linux/fcntl.h:

#define DN_ACCESS       0x00000001      /* File accessed */
#define DN_MODIFY       0x00000002      /* File modified */
#define DN_CREATE       0x00000004      /* File created */
#define DN_DELETE       0x00000008      /* File removed */
#define DN_RENAME       0x00000010      /* File renamed */
#define DN_ATTRIB       0x00000020      /* File changed attibutes */

It would probably be a simple exercise to add "DN_CLOSE",
and then run around and implement it.

(That being said, what was wrong with polling `lsof'
output for the absence of the file?)

On Sun, Apr 14, 2002 at 08:07:19AM -0500, John Fraser
wrote:
> 
> In most cases it will be Samba users putting the files onto the ext3
> filesystem that we need to process immediatitely, and we will also need to
> allow NFS users to put files onto the ext3 filesystem.  In both cases, we
> need low-level knowledge of when the file is written completely so we can
> grab the sucker right away.
> 
You can hack Samba so that it notifies you when a file has closed;
however, in the case of the case of NFS, there is no concept of "file
being closed", since NFS is a stateless protocol.  The best you could
do is "file hasn't been modified for n seconds".

						- Ted