Persistent module data

Persistent module data

[sirpj]

Hi,

I signed up a while ago. Because I am working at LLNL as an Intern and
have been given a neat assignment that involves coding some extensions
to reiser. I am implementing a file queueing mechanism that maintains
files as they are written in FIFO order. When you call ioctl() the 'next
file' in the queue is returned.

I have the FIFO queue implemented as a linked list that keeps track of
the file names and directory inodes that they are associated with. (This
was my first stab at it).

My question is about data preservation from inside a FS... I want to
preserve the contents of my queue in case of a crash. When mount is
called I want to scan this list and rebuild the queues in memory. Is it
possible to write data out to a persistent file from within the system?
Would using the module parameter approach be a good way to go? . . . But
from what I understand it wouldn't necessarily export the data if the
system hangs and the module can't be removed.

If anyone can help, has ideas, or some pointers, I would be very
grateful.

Thank You so much!

Jenn

Re: Persistent module data

[Swapnil Nagle]

> My question is about data preservation from inside a FS... I want to
> preserve the contents of my queue in case of a crash. When mount is
> called I want to scan this list and rebuild the queues in memory. Is it
> possible to write data out to a persistent file from within the system?

One way is to write the data out to a character device and have a 
userspace program poll for it.

Regards,
Swapnil.

Re: Persistent module data

[Jeff Mahoney]

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sirpj@ecs.csus.edu wrote:
| Hi,
|
| I signed up a while ago. Because I am working at LLNL as an Intern and
| have been given a neat assignment that involves coding some extensions
| to reiser. I am implementing a file queueing mechanism that maintains
| files as they are written in FIFO order. When you call ioctl() the 'next
| file' in the queue is returned.
|
| I have the FIFO queue implemented as a linked list that keeps track of
| the file names and directory inodes that they are associated with. (This
| was my first stab at it).
|
| My question is about data preservation from inside a FS... I want to
| preserve the contents of my queue in case of a crash. When mount is
| called I want to scan this list and rebuild the queues in memory. Is it
| possible to write data out to a persistent file from within the system?
| Would using the module parameter approach be a good way to go? . . . But
| from what I understand it wouldn't necessarily export the data if the
| system hangs and the module can't be removed.
|
| If anyone can help, has ideas, or some pointers, I would be very
| grateful.

For pointers on how to do this, have a look at the reiserfs xattr
implementation. It manages normal files itself and hides them from the
user. Since you're working with reiserfs, you could probably put the
file underneath the .reiserfs_priv directory, and get all the hiding for
free.

- -Jeff

- --
Jeff Mahoney
SuSE Labs
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Re: Persistent module data

[sirpj]

Hi,

Thanks. Is there anyway to do it without user space interation though?
(Even if it is not the most desireable approach) I was thinking about
allocating my own inode, from whithin the FS code, for a disk block and
storing the data there... similar to what a journal does.

I was hoping there would be a better or easier way...?

Jenn

>One way is to write the data out to a character device and have a
>userspace program poll for it.

>Regards,
>Swapnil.