User space data

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I want to be able to share a dynamic binary tree which is part of a user
process in the kernel space. The tree will be used as shared data
between user space process and kernel thread. Is this something that can
be accomplished using the mmap() facility? Is there better alternative
to achieve this? The pointers used in the data structure will be a issue
for sure.

The other option would be to add some messages between the user process
and the kernel and sync up the trees. I am trying to avoid this to avoid
synchronization issues.


Re: User space data
The "Unix way" would be to make it a file and/or a directory structure
from user view, doing a driver that offers "open" "read", etc.


Re: User space data

Are you referring to writing the binary tree to a file? Can you elaborate?


Michael Schnell wrote:
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Re: User space data
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Why not ?

 > Can you elaborate?

The user program can do (e.g.) seek() and read()/write(). These calls
are transferred 1:1 to the driver. So (AFAIK) a seek to n+1 and read a
byte does not necessary need to offer the same byte as the second byte
of two bytes read after seeking to n. Moreover the result of a read can
change dynamically with any instance.

So a seek could provide a "tree address" of some kind (e.g. each bit a
path though the binary tree) and a read could return the leaf data
(maybe including some kind of linked list data (next/previous leaf) if

Overwriting a leaf would be similar as reading, creating a new leaf
might use seek(,,end).

Moreover there are ioctl() calls that can be used for configuration or
other special purposes.


Re: User space data

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Not quite the same thing, but SNOBOL (a very early string processing
language, which pioneered what had become regular expressions) had
user-definable, arbitrary data structures. Binary trees were easily doable...

In the above scenario, all you really need to provide is a direction to
the next node/leaf.  So a seek for a binary tree has 3 directions:
parent, left child, right child, for a ternary tree it has 4 directions,
and for an arbitrary n tree it has up to n+1 directions...  Although that
can be simplified to 4 by using parent, left sibling, right
sibling, and child.

There is considerable prior art in implementing these kinds of data
structures...  So a bit of research might yield good results...


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